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Title: Seasoning of Wood
Author: Wagner, J. B. (Joseph Bernard), 1870-
Language: English
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SEASONING OF WOOD
A TREATISE ON THE NATURAL AND ARTIFICIAL
PROCESSES EMPLOYED IN THE PREPARATION
OF LUMBER FOR MANUFACTURE,
WITH DETAILED EXPLANATIONS OF ITS
USES, CHARACTERISTICS AND PROPERTIES
_ILLUSTRATIONS_
BY
JOSEPH B. WAGNER
AUTHOR OF "COOPERAGE"
[Illustration]
NEW YORK
D. VAN NOSTRAND COMPANY
25 PARK PLACE
1917
COPYRIGHT, 1917, BY
D. VAN NOSTRAND COMPANY
THE·PLIMPTON·PRESS
NORWOOD·MASS·U·S·A
PREFACE
The seasoning and kiln-drying of wood is such an important process in
the manufacture of woods that a need for fuller information regarding
it, based upon scientific study of the behavior of various species at
different mechanical temperatures, and under different drying
processes is keenly felt. Everyone connected with the woodworking
industry, or its use in manufactured products, is well aware of the
difficulties encountered in properly seasoning or removing the
moisture content without injury to the timber, and of its
susceptibility to atmospheric conditions after it has been thoroughly
seasoned. There is perhaps no material or substance that gives up its
moisture with more resistance than wood does. It vigorously defies the
efforts of human ingenuity to take away from it, without injury or
destruction, that with which nature has so generously supplied it.
In the past but little has been known of this matter further than the
fact that wood contained moisture which had to be removed before the
wood could be made use of for commercial purposes. Within recent
years, however, considerable interest has been awakened among
wood-users in the operation of kiln-drying. The losses occasioned in
air-drying and improper kiln-drying, and the necessity for getting the
material dry as quickly as possible after it has come from the saw, in
order to prepare it for manufacturing purposes, are bringing about a
realization of the importance of a technical knowledge of the subject.
Since this particular subject has never before been represented by any
technical work, and appears to have been neglected, it is hoped that
the trade will appreciate the endeavor in bringing this book before
them, as well as the difficulties encountered in compiling it, as it
is the first of its kind in existence. The author trusts that his
efforts will present some information that may be applied with
advantage, or serve at least as a matter of consideration or
investigation.
In every case the aim has been to give the facts, and wherever a
machine or appliance has been illustrated or commented upon, or the
name of the maker has been mentioned, it has not been with the
intention either of recommending or disparaging his or their work, but
has been made use of merely to illustrate the text.
The preparation of the following pages has been a work of pleasure to
the author. If they prove beneficial and of service to his
fellow-workmen he will have been amply repaid.
THE AUTHOR.
September, 1917
CONTENTS
SECTION I
TIMBER
PAGES
Characteristics and Properties of Same--Structure
of Wood--Properties of Wood--Classes of Trees 1-7
SECTION II
CONIFEROUS TREES
Wood of Coniferous Trees--Bark and Pith--Sapwood and Heartwood--The
Annual or Yearly Ring--Spring- and Summer-Wood--Anatomical
Structure--List of Important Coniferous Trees 8-30
SECTION III
BROAD-LEAVED TREES
Wood of Broad-leaved Trees--Minute Structure--List of Most
Important Broad-leaved Trees--Red Gum--Range of Red Gum--Form
of Red Gum--Tolerance of Red Gum--Its Demands upon Soil and
Moisture--Reproduction of Red Gum--Second-growth Red Gum--Tupelo
Gum--Uses of Tupelo Gum--Range of Tupelo Gum 31-85
SECTION IV
GRAIN, COLOR, ODOR, WEIGHT, AND FIGURE IN WOOD
Different Grains of Wood--Color and Odor of Wood--Weight of
Wood--Weight of Kiln-dried Wood of Different Species--Figure in
Wood 86-97
SECTION V
ENEMIES OF WOOD
General Remarks--Ambrosia or Timber Beetles--Round-headed
Borers--Flat-headed Borers--Timber Worms--Powder Post
Borers--Conditions Favorable for Insect Injury--Crude
Products--Round Timber with Bark on--How to Prevent
Injury--Saplings--Stave, Heading, and Shingle Bolts--Unseasoned
Products in the Rough--Seasoned Products in the Rough--Dry
Cooperage Stock and Wooden Truss Hoops--Staves and Heads
of Barrels Containing Alcoholic Liquids 98-113
SECTION VI
WATER IN WOOD
Distribution of Water in Wood--Seasonal Distribution of Water in
Wood--Composition of Sap--Effects of Moisture on Wood--The
Fibre-Saturation Point in Wood 114-118
SECTION VII
WHAT SEASONING IS
What Seasoning Is--Difference Between Seasoned and Unseasoned
Wood--Manner of Evaporation of Water--Absorption of Water
by Dry Wood--Rapidity of Evaporation--Physical Properties
that Influence Drying 119-127
SECTION VIII
ADVANTAGES OF SEASONING
Advantages of Seasoning--Prevention of Checking and
Splitting--Shrinkage of Wood--Expansion of Wood--Elimination of
Stain and Mildew 128-137
SECTION IX
DIFFICULTIES OF DRYING WOOD
Difficulties of Drying Wood--Changes Rendering Drying
Difficult--Losses Due to Improper Kiln-drying--Properties of
Wood that Effect Drying--Unsolved Problems in Kiln-drying 138-144
SECTION X
HOW WOOD IS SEASONED
Methods of Drying--Drying at Atmospheric Pressure--Drying Under
Pressure and Vacuum--Impregnation Methods--Preliminary
Treatments--Out-of-door Seasoning 145-155
SECTION XI
KILN-DRYING OF WOOD
Advantages of Kiln-drying over Air Drying--Physical Conditions
Governing the Drying of Wood--Theory of Kiln-drying--Requirements
in a Satisfactory Dry Kiln--Kiln-drying--Remarks--Underlying
Principles--Objects of Kiln-drying--Conditions of Success--Different
Treatments According to Kind--Temperature Depends--Air
Circulation--Humidity--Kiln-drying--Pounds of Water Lost in Drying
100 Pounds of Green Wood in the Kiln--Kiln-drying Gum--Preliminary
Steaming--Final Steaming--Kiln-drying of Green Red Gum 156-184
SECTION XII
TYPES OF DRY KILNS
Different types of Dry Kilns--The "Blower" or "Hot Blast" Dry
Kiln--Operating the "Blower" or "Hot Blast" Dry Kiln--The
"Pipe" or "Moist-Air" Dry Kiln--Operating the "Pipe" or
"Moist-Air" Dry Kiln--Choice of Drying Method--Kilns of
Different Types--The "Progressive" Dry Kiln--The "Apartment"
Dry Kiln--The "Pocket" Dry Kiln--The "Tower" Dry Kiln--The
"Box" Dry Kiln 185-205
SECTION XIII
DRY KILN SPECIALTIES
Kiln Cars and Method of Loading Same--The "Cross-wise" Piling
Method--The "End-wise" Piling Method--The "Edge-wise"
Piling Method--The Automatic Lumber Stacker--The Unstacker
Car--Stave Piling--Shingle Piling--Stave Bolt Trucks--Different
Types of Kiln Cars--Different Types of Transfer Cars--Dry Kiln
Doors--Different Types of Kiln Door Carriers 206-236
SECTION XIV
HELPFUL APPLIANCES IN KILN DRYING
The Humidity Diagram--Examples of Use--The Hygrodeik--The
Recording Hygrometer--The Registering Hygrometer--The
Recording Thermometer--The Registering Thermometer--The
Recording Steam Gauge--The Troemroid Scalometer--Test
Samples--Weighing--Examples of Use--Records of Moisture
Content--Saw Mills--Factories--The Electric Heater 237-250
SECTION XV
Bibliography--Glossary--Index of Latin Names--Index of Common
Names 251-257
LIST OF ILLUSTRATIONS
FIG. PAGE
1. Board of pine 13
2. Wood of spruce 14
3. Group of fibres from pine wood 15
4. Block of oak 31
5. Board of oak 32
6. Cross-section of oak highly magnified 32
7. Highly magnified fibres of wood 33
8. Isolated fibres and cells of wood 34
9. Cross-section of basswood 35
10. A large red gum 52
11. A tupelo gum slough 53
12. Second growth red gum 57
13. A cypress slough in dry season 58
14. A large cottonwood 78
15. Spiral grain in wood 87
16. Alternating spiral grain in cypress 87
17. Wavy grain in beech 88
18. Section of wood showing position of the grain at base of limb 89
19. Cross-section of a group of wood fibres 91
20. Isolated fibres of wood 91
21. Orientation of wood samples 93
22. Work of ambrosia beetles in tulip or yellow poplar 100
23. Work of ambrosia beetles in oak 100
24. Work of round-headed and flat-headed borers in pine 102
25. Work of timber worms in oak 103
26. Work of powder post borers in hickory poles 104
27. Work of powder post borers in hickory poles 104
28. Work of powder post borers in hickory handles 105
29. Work of round-headed borers in white pine staves 111
30. U. S. Forest Service humidity controlled dry kiln 161
31. Section through moist-air dry kiln 189
32. Live steam single pipe heating apparatus 190
33. Live steam double pipe heating apparatus 191
34. Vertical Pipe heating apparatus 193
35. Progressive dry kilns 197
36. Apartment dry kilns 199
37. Pocket dry kilns 201
38. Tower dry kiln 203
39. Box dry kiln 205
40. Edge-wise method of piling 206
41. Edge-wise method of piling 207
42. Automatic lumber stacker 208
43. Automatic lumber stacker 208
44. Battery of three automatic lumber stackers 209
45. Battery of three automatic lumber stackers 209
46. Lumber loaded edge-wise on kiln truck 210
47. The lumber unstacker 211
48. The lumber unstacker car 211
49. Method of piling veneer on edge 212
50. Kiln truck loaded cross-wise of kiln 213
51. Kiln truck loaded cross-wise of kiln 214
52. Kiln truck loaded end-wise of kiln 214
53. Kiln truck loaded end-wise of kiln 215
54. Method of piling staves on kiln truck 216
55. Method of piling staves on kiln truck 216
56. Method of piling tub or pail staves on kiln truck 217
57. Method of piling bundled staves on kiln truck 217
58. Method of piling shingles on kiln truck 218
59. Method of piling shingles on kiln truck 218
60. Method of piling shingles on kiln truck 219
61. Kiln truck designed for loose pail staves 219
62. Kiln truck designed for handling short stock 221
63. Stave bolt truck 221
64. Stave bolt truck 222
65. Stave bolt truck 222
66. Stave bolt truck 223
67. Stave bolt truck 223
68. Stave bolt truck 224
69. Regular 3-rail transfer car 224
70. Regular 3-rail transfer car 225
71. Special 4-rail transfer car 225
72. Regular 2-rail transfer car 225
73. Regular 2-rail transfer car 226
74. Underslung type 3-rail transfer car 226
75. Underslung type 2-rail transfer car 226
76. Flexible type 2-rail transfer car 227
77. Regular transfer car for stave bolt trucks 228
78. Regular transfer car for stave bolt trucks 228
79. Special transfer car for stave bolt trucks 228
80. Regular channel iron kiln truck for cross-wise piling 229
81. Regular channel iron kiln truck for cross-wise piling 229
82. Regular channel iron kiln truck for end-wise piling 230
83. Special channel iron kiln truck for end-wise piling 230
84. Regular dolly kiln truck for end-wise piling 230
85. Asbestos-lined kiln door 231
86. Twin door carrier with door loaded 232
87. Twin door carrier for doors 18 to 35 feet wide 232
88. Kiln door carrier 233
89. Kiln door construction 234
90. Kiln door construction 235
91. Kiln door construction 235
92. Kiln door construction 236
93. The Humidity diagram _facing_ 237
94. The hygrodeik 242
95. The recording hygrometer 243
96. The registering hygrometer 244
97. The recording thermometer 245
98. The registering thermometer 246
99. The recording steam gauge 246
100. The troemroid scalometer 247
101. The electric heater 250
SEASONING OF WOOD
SECTION I
TIMBER
Characteristics and Properties
Timber was probably one of the earliest, if not the earliest, of
materials used by man for constructional purposes. With it he built
for himself a shelter from the elements; it provided him with fuel and
oft-times food, and the tree cut down and let across a stream formed
the first bridge. From it, too, he made his "dug-out" to travel along
and across the rivers of the district in which he dwelt; so on down
through the ages, for shipbuilding and constructive purposes, timber
has continued to our own time to be one of the most largely used of
nature's products.
Although wood has been in use so long and so universally, there still
exists a remarkable lack of knowledge regarding its nature, not only
among ordinary workmen, but among those who might be expected to know
its properties. Consequently it is often used in a faulty and wasteful
manner. Experience has been almost the only teacher, and
theories--sometimes right, sometimes wrong--rather than well
substantiated facts, lead the workman.
One reason for this imperfect knowledge lies in the fact that wood is
not a homogeneous material, but a complicated structure, and so
variable, that one piece will behave very differently from another,
although cut from the same tree. Not only does the wood of one species
differ from that of another, but the butt cut differs from that of the
top log, the heartwood from the sapwood; the wood of quickly-grown
sapling of the abandoned field, from that of the slowly-grown, old
monarch of the forest. Even the manner in which the tree was cut and
kept influences its behavior and quality. It is therefore extremely
difficult to study the material for the purpose of establishing
general laws.
The experienced woodsman will look for straight-grained, long-fibred
woods, with the absence of disturbing resinous and coloring matter,
knots, etc., and will quickly distinguish the more porous red or black
oaks from the less porous white species, _Quercus alba_. That the
inspection should have regard to defects and unhealthy conditions
(often indicated by color) goes without saying, and such inspection is
usually practised. That knots, even the smallest, are defects, which
for some uses condemn the material entirely, need hardly be mentioned.
But that "season-checks," even those that have closed by subsequent
shrinkage, remain elements of weakness is not so readily appreciated;
yet there cannot be any doubt of this, since these, the intimate
connections of the wood fibres, when once interrupted are never
reestablished.
Careful woods-foremen and manufacturers, therefore, are concerned as
to the manner in which their timber is treated after the felling, for,
according to the more or less careful seasoning of it, the season
checks--not altogether avoidable--are more or less abundant.
There is no country where wood is more lavishly used or criminally
neglected than in the United States, and none in which nature has more
bountifully provided for all reasonable requirements.
In the absence of proper efforts to secure reproduction, the most
valuable kinds are rapidly being decimated, and the necessity of a
more rational and careful use of what remains is clearly apparent. By
greater care in selection, however, not only will the duration of the
supply be extended, but more satisfactory results will accrue from its
practice.
There are few more extensive and wide-reaching subjects on which to
treat than timber, which in this book refers to dead timber--the
timber of commerce--as distinct from the living tree. Such a great
number of different kinds of wood are now being brought from various
parts of the world, so many new kinds are continually being added, and
the subject is more difficult to explain because timber of practically
the same character which comes from different localities goes under
different names, that if one were always to adhere to the botanical
name there would be less confusion, although even botanists differ in
some cases as to names. Except in the cases of the older and better
known timbers, one rarely takes up two books dealing with timber and
finds the botanical names the same; moreover, trees of the same
species may produce a much poorer quality of timber when obtained from
different localities in the same country, so that botanical knowledge
will not always allow us to dispense with other tests.
The structure of wood affords the only reliable means of
distinguishing the different kinds. Color, weight, smell, and other
appearances, which are often direct or indirect results of structure,
may be helpful in this distinction, but cannot be relied upon
entirely. Furthermore, structure underlies nearly all the technical
properties of this important product, and furnishes an explanation why
one piece differs in these properties from another. Structure explains
why oak is heavier, stronger, and tougher than pine; why it is harder
to saw and plane, and why it is so much more difficult to season
without injury. From its less porous structure alone it is evident
that a piece of young and thrifty oak is stronger than the porous wood
of an old or stunted tree, or that a Georgia or long-leaf pine excels
white pine in weight and strength.
Keeping especially in mind the arrangement and direction of the fibres
of wood, it is clear at once why knots and "cross-grain" interfere
with the strength of timber. It is due to the structural peculiarities
that "honeycombing" occurs in rapid seasoning, that checks or cracks
extend radially and follow pith rays, that tangent or "bastard" cut
stock shrinks and warps more than that which is quarter-sawn. These
same peculiarities enable oak to take a better finish than basswood or
coarse-grained pine.
Structure of Wood
The softwoods are made up chiefly of tracheids, or vertical cells
closed at the ends, and of the relatively short parenchyma cells of
the medullary rays which extend radially from the heart of the tree.
The course of the tracheids and the rays are at right angles to each
other. Although the tracheids have their permeable portions or pits in
their walls, liquids cannot pass through them with the greatest ease.
The softwoods do not contain "pores" or vessels and are therefore
called "non-porous" woods.
The hardwoods are not so simple in structure as softwoods. They
contain not only rays, and in many cases tracheids, but also
thick-walled cells called fibres and wood parenchyma for the storage
of such foods as starches and sugars. The principal structural
features of the hardwoods are the pores or vessels. These are long
tubes, the segments of which are made up of cells which have lost
their end walls and joined end to end, forming continuous "pipe lines"
from the roots to the leaves in the tree. Since they possess pores or
vessels, the hardwoods are called "porous" woods.
Red oak is an excellent example of a porous wood. In white oak the
vessels of the heartwood especially are closed, very generally by
ingrowths called tyloses. This probably explains why red oak dries
more easily and rapidly than white oak.
The red and black gums are perhaps the simplest of the hardwoods in
structure. They are termed "diffuse porous" woods because of the
numerous scattered pores they contain. They have only vessels, wood
fibres, and a few parenchyma cells. The medullary rays, although
present, are scarcely visible in most instances. The vessels are in
many cases open, and might be expected to offer relatively little
resistance to drying.
Properties of Wood
Certain general properties of wood may be discussed briefly. We know
that wood substance has the property of taking in moisture from the
air until some balance is reached between the humidity of the air and
the moisture in the wood. This moisture which goes into the cell walls
hygroscopic moisture, and the property which the wood substance has of
taking on hygroscopic moisture is termed hygroscopicity. Usually wood
contains not only hygroscopic moisture but also more or less free
water in the cell cavities. Especially is this true of sapwood. The
free water usually dries out quite rapidly with little or no shrinkage
or other physical change.
In certain woods--for example, _Eucalyptus globulus_ and possibly some
oaks--shrinkage begins almost at once, thus introducing a factor at
the very start of the seasoning process which makes these woods very
refractory.
The cell walls of some species, including the two already mentioned,
such as Western red cedar and redwood, become soft and plastic when
hot and moist. If the fibres are hot enough and very wet, they are not
strong enough to withstand the resulting force of the atmospheric
pressure and the tensile force exerted by the departing free water,
and the result is that the cells actually collapse.
In general, however, the hygroscopic moisture necessary to saturate
the cell walls is termed the "fibre saturation point." This amount has
been found to be from 25 to 30 per cent of the dry wood weight. Unlike
_Eucalyptus globulus_ and certain oaks, the gums do not begin to
shrink until the moisture content has been reduced to about 30 per
cent of the dry wood weight. These woods are not subject to collapse,
although their fibres become very plastic while hot and moist.
Upon the peculiar properties of each wood depends the difficulty or
ease of the seasoning process.
Classes of Trees
The timber of the United States is furnished by three well-defined
classes of trees: (1) The needle-leaved, naked-seeded conifers, such
as pine, cedar, etc., (2) the broad-leaved trees such as oak poplar,
etc., and (3) to an inferior extent by the (one-seed leaf) palms,
yuccas, and their allies, which are confined to the most southern
parts of the country.
Broad-leaved trees are also known as deciduous trees, although,
especially in warm countries, many of them are evergreen, while the
needle-leaved trees (conifers) are commonly termed "evergreens,"
although the larch, bald cypress, and others shed their leaves every
fall, and even the names "broad-leaved" and "coniferous," though
perhaps the most satisfactory, are not at all exact, for the conifer
"ginkgo" has broad leaves and bears no cones.
Among the woodsmen, the woods of broad-leaved trees are known as
"hardwoods," though poplar is as soft as pine, and the "coniferous
woods" are known as "softwoods," notwithstanding the fact that yew
ranks high in hardness even when compared with "hardwoods."
Both in the number of different kinds of trees or species and still
more in the importance of their product, the conifers and broad-leaved
trees far excel the palms and their relatives.
In the manner of their growth both the conifers and broad-leaved trees
behave alike, adding each year a new layer of wood, which covers the
old wood in all parts of the stem and limbs. Thus the trunk continues
to grow in thickness throughout the life of the tree by additions
(annual rings), which in temperate climates are, barring accidents,
accurate records of the tree. With the palms and their relatives the
stem remains generally of the same diameter, the tree of a hundred
years old being as thick as it was at ten years, the growth of these
being only at the top. Even where a peripheral increase takes place,
as in the yuccas, the wood is not laid on in well-defined layers for
the structure remains irregular throughout. Though alike in the manner
of their growth, and therefore similar in their general make-up,
conifers and broad-leaved trees differ markedly in the details of
their structure and the character of their wood.
The wood of all conifers is very simple in its structure, the fibres
composing the main part of the wood all being alike and their
arrangement regular. The wood of the broad-leaved trees is complex in
structure; it is made up of different kinds of cells and fibres and
lacks the regularity of arrangement so noticeable in the conifers.
This difference is so great that in a study of wood structure it is
best to consider the two kinds separately.
In this country the great variety of woods, and especially of useful
woods, often makes the mere distinction of the kind or species of tree
most difficult. Thus there are at least eight pines of the thirty-five
native ones in the market, some of which so closely resemble each
other in their minute structure that one can hardly tell them apart,
and yet they differ in quality and are often mixed or confounded in
the trade. Of the thirty-six oaks, of which probably not less than six
or eight are marketed, we can readily recognize by means of their
minute anatomy at least two tribes--the white and black oaks. The same
is true of the eleven kinds of hickory, the six kinds of ash, etc.,
etc.
The list of names of all trees indigenous to the United States, as
enumerated by the United States Forest Service, is 495 in number, the
designation of "tree" being applied to all woody plants which produce
naturally in their native habitat one main, erect stem, bearing a
definite crown, no matter what size they attain.
Timber is produced only by the Spermatophyta, or seed-bearing plants,
which are subdivided into the Gymnosperms (conifers), and Angiosperms
(broad-leaved). The conifer or cone-bearing tree, to which belong the
pines, larches, and firs, is one of the three natural orders of
Gymnosperms. These are generally classed as "softwoods," and are more
extensively scattered and more generally used than any other class of
timber, and are simple and regular in structure. The so-called
"hardwoods" are "Dicotyledons" or broad-leaved trees, a subdivision of
the Angiosperms. They are generally of slower growth, and produce
harder timber than the conifers, but not necessarily so. Basswood,
poplar, sycamore, and some of the gums, though classed with the
hardwoods, are not nearly as hard as some of the pines.
SECTION II
CONIFEROUS TREES
WOOD OF THE CONIFEROUS TREES
Examining a smooth cross-section or end face of a well-grown log of
Georgia pine, we distinguish an envelope of reddish, scaly bark, a
small, whitish pith at the center, and between these the wood in a
great number of concentric rings.
Bark and Pith
The bark of a pine stem is thickest and roughest near the base,
decreases rapidly in thickness from one to one-half inches at the
stump to one-tenth inch near the top of the tree, and forms in general
about ten to fifteen per cent of the entire trunk. The pith is quite
thick, usually one-eighth to one-fifth inch in southern species,
though much less so in white pine, and is very thin, one-fifteenth to
one twenty-fifth inch in cypress, cedar, and larch.
In woods with a thick pith, the pith is finest at the stump, grows
rapidly thicker toward the top, and becomes thinner again in the crown
and limbs, the first one to five rings adjoining it behaving
similarly.
What is called the pith was once the seedling tree, and in many of the
pines and firs, especially after they have been seasoning for a good
while, this is distinctly noticeable in the center of the log, and
detaches itself from the surrounding wood.
Sap and Heartwood
Wood is composed of duramen or heartwood, and alburnum or sapwood, and
when dry consists approximately of 49 per cent by weight of carbon, 6
per cent of hydrogen, 44 per cent of oxygen, and 1 per cent of ash,
which is fairly uniform for all species. The sapwood is the external
and youngest portion of the tree, and often constitutes a very
considerable proportion of it. It lies next the bark, and after a
course of years, sometimes many, as in the case of oaks, sometimes
few, as in the case of firs, it becomes hardened and ultimately forms
the duramen or heartwood. Sapwood is generally of a white or light
color, almost invariably lighter in color than the heartwood, and is
very conspicuous in the darker-colored woods, as for instance the
yellow sapwood of mahogany and similiar colored woods, and the reddish
brown heartwood; or the yellow sapwood of _Lignum-vitae_ and the dark
green heartwood. Sapwood forms a much larger proportion of some trees
than others, but being on the outer circumference it always forms a
large proportion of the timber, and even in sound, hard pine will be
from 40 per cent to 60 per cent of the tree and in some cases much
more. It is really imperfect wood, while the duramen or heartwood is
the perfect wood; the heartwood of the mature tree was the sapwood of
its earlier years. Young trees when cut down are almost all sapwood,
and practically useless as good, sound timber; it is, however, through
the sapwood that the life-giving juices which sustain the tree arise
from the soil, and if the sapwood be cut through, as is done when
"girdling," the tree quickly dies, as it can derive no further
nourishment from the soil. Although absolutely necessary to the
growing tree, sapwood is often objectionable to the user, as it is the
first part to decay. In this sapwood many cells are active, store up
starch, and otherwise assist in the life processes of the tree,
although only the last or outer layer of cells forms the growing part,
and the true life of the tree.
The duramen or heartwood is the inner, darker part of the log. In the
heartwood all the cells are lifeless cases, and serve only the
mechanical function of keeping the tree from breaking under its own
great weight or from being laid low by the winds. The darker color of
the heartwood is due to infiltration of chemical substances into the
cell walls, but the cavities of the cells in pine are not filled up,
as is sometimes believed, nor do their walls grow thicker, nor are the
walls any more liquified than in the sapwood.
Sapwood varies in width and in the number of rings which it contains
even in different parts of the same tree. The same year's growth which
is sapwood in one part of a disk may be heartwood in another. Sapwood
is widest in the main part of the stem and often varies within
considerable limits and without apparent regularity. Generally, it
becomes narrower toward the top and in the limbs, its width varying
with the diameter, and being the least in a given disk on the side
which has the shortest radius. Sapwood of old and stunted pines is
composed of more rings than that of young and thrifty specimens. Thus
in a pine two hundred and fifty years old a layer of wood or an annual
ring does not change from sapwood to heartwood until seventy or eighty
years after it is formed, while in a tree one hundred years old or
less it remains sapwood only from thirty to sixty years.
The width of the sapwood varies considerably for different kinds of
pine. It is small for long-leaf and white pine and great for loblolly
and Norway pines. Occupying the peripheral part of the trunk, the
proportion which it forms of the entire mass of the stem is always
great. Thus even in old long-leaf pines, the sapwood forms 40 per cent
of the merchantable log, while in the loblolly and in all young trees
the sapwood forms the bulk of the wood.
The Annual or Yearly Rings
The concentric annual or yearly rings which appear on the end face of
a log are cross-sections of so many thin layers of wood. Each such
layer forms an envelope around its inner neighbor, and is in turn
covered by the adjoining layer without, so that the whole stem is
built up of a series of thin, hollow cylinders, or rather cones.
A new layer of wood is formed each season, covering the entire stem,
as well as all the living branches. The thickness of this layer or the
width of the yearly ring varies greatly in different trees, and also
in different parts of the same tree.
In a normally-grown, thrifty pine log the rings are widest near the
pith, growing more and more narrow toward the bark. Thus the central
twenty rings in a disk of an old long-leaf pine may each be one-eighth
to one-sixth inch wide, while the twenty rings next to the bark may
average only one-thirtieth inch.
In our forest trees, rings of one-half inch in width occur only near
the center in disks of very thrifty trees, of both conifers and
hardwoods. One-twelfth inch represents good, thrifty growth, and the
minimum width of one two hundred inch is often seen in stunted spruce
and pine. The average width of rings in well-grown, old white pine
will vary from one-twelfth to one-eighteenth inch, while in the slower
growing long-leaf pine it may be one twenty-fifth to one-thirtieth of
an inch. The same layer of wood is widest near the stump in very
thrifty young trees, especially if grown in the open park; but in old
forest trees the same year's growth is wider at the upper part of the
tree, being narrowest near the stump, and often also near the very tip
of the stem. Generally the rings are widest near the center, growing
narrower toward the bark.
In logs from stunted trees the order is often reversed, the interior
rings being thin and the outer rings widest. Frequently, too, zones or
bands of very narrow rings, representing unfavorable periods of
growth, disturb the general regularity.
Few trees, even among pines, furnish a log with truly circular
cross-section. Usually it is an oval, and at the stump commonly quite
an irregular figure. Moreover, even in very regular or circular disks
the pith is rarely in the center, and frequently one radius is
conspicuously longer than its opposite, the width of some rings, if
not all, being greater on one side than on the other. This is nearly
always so in the limbs, the lower radius exceeding the upper. In
extreme cases, especially in the limbs, a ring is frequently
conspicuous on one side, and almost or entirely lost to view on the
other. Where the rings are extremely narrow, the dark portion of the
ring is often wanting, the color being quite uniform and light. The
greater regularity or irregularity of the annual rings has much to do
with the technical qualities of the timber.
Spring- and Summer-Wood
Examining the rings more closely, it is noticed that each ring is made
up of an inner, softer, light-colored and an outer, or peripheral,
firmer and darker-colored portion. Being formed in the forepart of the
season, the inner, light-colored part is termed spring-wood, the
outer, darker-portioned being the summer-wood of the ring. Since the
latter is very heavy and firm it determines to a very large extent the
weight and strength of the wood, and as its darker color influences
the shade of color of the entire piece of wood, this color effect
becomes a valuable aid in distinguishing heavy and strong from light
and soft pine wood.
In most hard pines, like the long-leaf, the dark summer-wood appears
as a distinct band, so that the yearly ring is composed of two sharply
defined bands--an inner, the spring-wood, and an outer, the
summer-wood. But in some cases, even in hard pines, and normally in
the woods of white pines, the spring-wood passes gradually into the
darker summer-wood, so that a darkly defined line occurs only where
the spring-wood of one ring abuts against the summer-wood of its
neighbor. It is this clearly defined line which enables the eye to
distinguish even the very narrow lines in old pines and spruces.
In some cases, especially in the trunks of Southern pines, and
normally on the lower side of pine limbs, there occur dark bands of
wood in the spring-wood portion of the ring, giving rise to false
rings, which mislead in a superficial counting of rings. In the disks
cut from limbs these dark bands often occupy the greater part of the
ring, and appear as "lunes," or sickle-shaped figures. The wood of
these dark bands is similar to that of the true summer-wood. The cells
have thick walls, but usually the compressed or flattened form.
Normally, the summer-wood forms a greater proportion of the rings in
the part of the tree formed during the period of thriftiest growth. In
an old tree this proportion is very small in the first two to five
rings about the pith, and also in the part next to the bark, the
intermediate part showing a greater proportion of summer-wood. It is
also greatest in a disk taken from near the stump, and decreases
upward in the stem, thus fully accounting for the difference in weight
and firmness of the wood of these different parts.
[Illustration: Fig. 1. Board of Pine. CS, cross-section; RS,
radial section; TS, tangential section; _sw_, summer-wood;
_spw_, spring-wood.]
In the long-leaf pine the summer-wood often forms scarcely ten per
cent of the wood in the central five rings; forty to fifty per cent of
the next one hundred rings, about thirty per cent of the next fifty,
and only about twenty per cent in the fifty rings next to the bark. It
averages forty-five per cent of the wood of the stump and only
twenty-four per cent of that of the top.
Sawing the log into boards, the yearly rings are represented on the
board faces of the middle board (radial sections) by narrow parallel
strips (see Fig. 1), an inner, lighter stripe and its outer, darker
neighbor always corresponding to one annual ring.
On the faces of the boards nearest the slab (tangential or bastard
boards) the several years' growth should also appear as parallel, but
much broader stripes. This they do if the log is short and very
perfect. Usually a variety of pleasing patterns is displayed on the
boards, depending on the position of the saw cut and on the regularity
of growth of the log (see Fig. 1). Where the cut passes through a
prominence (bump or crook) of the log, irregular, concentric circlets
and ovals are produced, and on almost all tangent boards arrow or
V-shaped forms occur.
Anatomical Structure
Holding a well-smoothed disk or cross-section one-eighth inch thick
toward the light, it is readily seen that pine wood is a very porous
structure. If viewed with a strong magnifier, the little tubes,
especially in the spring-wood of the rings, are easily distinguished,
and their arrangement in regular, straight, radial rows is apparent.
[Illustration: Fig. 2. Wood of Spruce. 1, natural size; 2,
small part of one ring magnified 100 times. The vertical
tubes are wood fibres, in this case all "tracheids." _m_,
medullary or pith ray; _n_, transverse tracheids of ray; _a_,
_b_, and _c_, bordered pits of the tracheids, more enlarged.]
Scattered through the summer-wood portion of the rings, numerous
irregular grayish dots (the resin ducts) disturb the uniformity and
regularity of the structure. Magnified one hundred times, a piece of
spruce, which is similar to pine, presents a picture like that shown
in Fig. 2. Only short pieces of the tubes or cells of which the wood
is composed are represented in the picture. The total length of these
fibres is from one-twentieth to one-fifth inch, being the smallest
near the pith, and is fifty to one hundred times as great as their
width (see Fig. 3). They are tapered and closed at their ends,
polygonal or rounded and thin-walled, with large cavity, lumen or
internal space in the spring-wood, and thick-walled and flattened
radially, with the internal space or lumen much reduced in the
summer-wood (see right-hand portion of Fig. 2). This flattening,
together with the thicker walls of the cells, which reduces the lumen,
causes the greater firmness and darker color of the summer-wood.
There is more material in the same volume. As shown in the figure, the
tubes, cells or "tracheids" are decorated on their walls by
circlet-like structures, the "bordered pits," sections of which are
seen more magnified as _a_, _b_, and _c_, Fig. 2. These pits are in
the nature of pores, covered by very thin membranes, and serve as
waterways between the cells or tracheids. The dark lines on the side
of the smaller piece (1, Fig. 2) appear when magnified (in 2, Fig. 2)
as tiers of eight to ten rows of cells, which run radially (parallel
to the rows of tubes or tracheids), and are seen as bands on the
radial face and as rows of pores on the tangential face. These bands
or tiers of cell rows are the medullary rays or pith rays, and are
common to all our lumber woods.
In the pines and other conifers they are quite small, but they can
readily be seen even without a magnifier. If a radial surface of
split-wood (not smoothed) is examined, the entire radial face will be
seen almost covered with these tiny structures, which appear as fine
but conspicuous cross-lines. As shown in Fig. 2, the cells of the
medullary or pith are smaller and very much shorter than the wood
fibre or tracheids, and their long axis is at right angles to that of
the fiber.
[Illustration: Fig. 3. Group of Fibres from Pine Wood. Partly
schematic. The little circles are "border pits" (see Fig. 2,
_a-c_). The transverse rows of square pits indicate the
places of contact of these fibres and the cells of the
neighboring pith rays. Magnified about 25 times.]
In pines and spruces the cells of the upper and lower rows of each
tier or pith ray have "bordered" pits, like those of the wood fibre or
tracheids proper, but the cells of the intermediate rows in the rays
of cedars, etc., have only "simple" pits, _i.e._, pits devoid of the
saucer-like "border" or rim. In pine, many of the pith rays are larger
than the majority, each containing a whitish line, the horizontal
resin duct, which, though much smaller, resembles the vertical ducts
on the cross-section. The larger vertical resin ducts are best
observed on removal of the bark from a fresh piece of white pine cut
in the winter where they appear as conspicuous white lines, extending
often for many inches up and down the stem. Neither the horizontal nor
the vertical resin ducts are vessels or cells, but are openings
between cells, _i.e._, intercellular spaces, in which the resin
accumulates, freely oozing out when the ducts of a fresh piece of
sapwood are cut. They are present only in our coniferous woods, and
even here they are restricted to pine, spruce, and larch, and are
normally absent in fir, cedar, cypress, and yew. Altogether, the
structure of coniferous woods is very simple and regular, the bulk
being made up of the small fibres called tracheids, the disturbing
elements of pith rays and resin ducts being insignificant, and hence
the great uniformity and great technical value of coniferous woods.
LIST OF IMPORTANT CONIFEROUS WOODS
CEDAR
Light soft, stiff, not strong, of fine texture. Sap- and heartwood
distinct, the former lighter, the latter a dull grayish brown or red.
The wood seasons rapidly, shrinks and checks but little, and is very
durable in contact with the soil. Used like soft pine, but owing to
its great durability preferred for shingles, etc. Cedars usually occur
scattered, but they form in certain localities forests of considerable
extent.
(_a_) White Cedars
=1. White Cedar= (_Thuya occidentalis_) (Arborvitæ, Tree of Life).
Heartwood light yellowish brown, sapwood nearly white. Wood light,
soft, not strong, of fine texture, very durable in contact with the
soil, very fragrant. Scattered along streams and lakes, frequently
covering extensive swamps; rarely large enough for lumber, but
commonly used for fence posts, rails, railway ties, and shingles. This
species has been extensively cultivated as an ornamental tree for at
least a century. Maine to Minnesota and northward.
=2. Canoe Cedar= (_Thuya gigantea_) (Red Cedar of the West). In Oregon
and Washington a very large tree, covering extensive swamps; in the
mountains much smaller, skirting the water courses. An important
lumber tree. The wood takes a fine polish; suitable for interior
finishing, as there is much variety of shading in the color.
Washington to northern California and eastward to Montana.
=3. White Cedar= (_Chamæcyparis thyoides_). Medium-sized tree. Heartwood
light brown with rose tinge, sapwood paler. Wood light, soft, not
strong, close-grained, easily worked, very durable in contact with the
soil and very fragrant. Used in boatbuilding cooperage, interior
finish, fence posts, railway ties, etc. Along the coast from Maine to
Mississippi.
=4. White Cedar= (_Chamæcyparis Lawsoniana_) (Port Orford Cedar, Oregon
Cedar, Lawson's Cypress, Ginger Pine). A very large tree. A fine,
close-grained, yellowish-white, durable timber, elastic, easily
worked, free of knots, and fragrant. Extensively cut for lumber;
heavier and stronger than any of the preceding. Along the coast line
of Oregon.
=5. White Cedar= (_Libocedrus decurrens_) (Incense Cedar). A large tree,
abundantly scattered among pine and fir. Wood fine-grained. Cascades
and Sierra Nevada Mountains of Oregon and California.
=6. Yellow Cedar= (_Cupressus nootkatensis_) (Alaska Cedar, Alaska
Cypress). A very large tree, much used for panelling and furniture. A
fine, close-grained, yellowish white, durable timber, easily worked.
Along the coast line of Oregon north.
(_b_) Red Cedars
=7. Red Cedar= (_Juniperus Virginiana_) (Savin Juniper, Juniper, Red
Juniper, Juniper Bush, Pencil Cedar). Heartwood dull red color, thin
sapwood nearly white. Close even grain, compact structure. Wood light,
soft, weak, brittle, easily worked, durable in contact with the soil,
and fragrant. Used for ties, posts, interior finish, pencil cases,
cigar boxes, silos, tanks, and especially for lead pencils, for which
purpose alone several million feet are cut each year. A small to
medium-sized tree scattered through the forests, or in the West
sparsely covering extensive areas (cedar brakes). The red cedar is the
most widely distributed conifer of the United States, occurring from
the Atlantic to the Pacific, and from Florida to Minnesota. Attains a
suitable size for lumber only in the Southern, and more especially the
Gulf States.
=8. Red Cedar= (_Juniperus communis_) (Ground Cedar). Small-sized tree,
its maximum height being about 25 feet. It is found widely distributed
throughout the Northern hemisphere. Wood in its quality similar to the
preceding. The fruit of this species is gathered in large quantities
and used in the manufacture of gin; whose peculiar flavor and
medicinal properties are due to the oil of Juniper berries, which is
secured by adding the crushed fruit to undistilled grain spirit, or by
allowing the vapor to pass over it before condensation. Used locally
for construction purposes, fence posts, etc. Ranges from Greenland to
Alaska, in the East, southward to Pennsylvania and northern Nebraska;
in the Rocky Mountains to Texas, Mexico, and Arizona.
=9. Redwood= (_Sequoia sempervirens_) (Sequoia, California Redwood,
Coast Redwood). Wood in its quality and uses like white cedar. Thick,
red heartwood, changing to reddish brown when seasoned. Thin sapwood,
nearly white, coarse, straight grain, compact structure. Light, not
strong, soft, very durable in contact with the soil, not resinous,
easily worked, does not burn easily, receives high polish. Used for
timber, shingles, flumes, fence posts, coffins, railway ties, water
pipes, interior decorations, and cabinetmaking. A very large tree,
limited to the coast ranges of California, and forming considerable
forests, which are rapidly being converted into lumber.
CYPRESS
=10. Cypress= (_Taxodium distinchum_) (Bald Cypress, Black, White, and
Red Cypress, Pecky Cypress). Wood in its appearance, quality, and uses
similar to white cedar. "Black" and "White Cypress" are heavy and
light forms of the same species. Heartwood brownish; sapwood nearly
white. Wood close, straight-grain, frequently full of small holes
caused by disease known as "pecky cypress." Greasy appearance and
feeling. Wood light, soft, not strong, durable in contact with the
soil, takes a fine polish. Green wood often very heavy. Used for
carpentry, building construction, shingles, cooperage, railway ties,
silos, tanks, vehicles, and washing machines. The cypress is a large,
deciduous tree, inhabiting swampy lands, and along rivers and coasts
of the Southern parts of the United States. Grows to a height of 150
feet and 12 feet in diameter.
FIR
This name is frequently applied to wood and to trees which are not
fir; most commonly to spruce, but also, especially in English markets,
to pine. It resembles spruce, but is easily distinguished from it, as
well as from pine and larch, by the absence of resin ducts. Quality,
uses, and habits similar to spruce.
=11. Balsam Fir= (_Abies balsamea_) (Balsam, Fir Tree, Balm of Gilead
Fir). Heartwood white to brownish; sapwood lighter color;
coarse-grained, compact structure, satiny. Wood light, not durable or
strong, resinous, easily split. Used for boxes, crates, doors,
millwork, cheap lumber, paper pulp. Inferior to white pine or spruce,
yet often mixed and sold with these species in the lumber market. A
medium-sized tree scattered throughout the northern pineries, and cut
in lumber operations whenever of sufficient size. Minnesota to Maine
and northward.
=12. White Fir= (_Abies grandis_ and _Abies concolor_). Medium-to very
large-sized tree, forming an important part of most of the Western
mountain forests, and furnishes much of the lumber of the respective
regions. The former occurs from Vancouver to California, and the
latter from Oregon to Arizona and eastward to Colorado and Mexico. The
wood is soft and light, coarse-grained, not unlike the "Swiss pine" of
Europe, but darker and firmer, and is not suitable for any purpose
requiring strength. It is used for boxes, barrels, and to a small
extent for wood pulp.
=13. White Fir= (_Abies amabalis_). Good-sized tree, often forming
extensive mountain forests. Wood similar in quality and uses to _Abies
grandis_. Cascade Mountains of Washington and Oregon.
=14. Red Fir= (_Abies nobilis_) (Noble Fir) (not to be confounded with
Douglas spruce. See No. 40). Large to very large-sized tree, forming
extensive forests on the slope of the mountains between 3,000 and
4,000 feet elevation. Cascade Mountains of Oregon.
=15. Red Fir= (_Abies magnifica_). Very large-sized tree, forming
forests about the base of Mount Shasta. Sierra Nevada Mountains of
California, from Mount Shasta southward.
HEMLOCK
Light to medium weight, soft, stiff, but brittle, commonly
cross-grained, rough and splintery. Sapwood and heartwood not well
defined. The wood of a light reddish-gray color, free from resin
ducts, moderately durable, shrinks and warps considerably in drying,
wears rough, retains nails firmly. Used principally for dimension
stuff and timbers. Hemlocks are medium- to large-sized trees, commonly
scattered among broad-leaved trees and conifers, but often forming
forests of almost pure growth.
=16. Hemlock= (_Tsuga canadensis_) (Hemlock Spruce, Peruche).
Medium-sized tree, furnishes almost all the hemlock of the Eastern
market. Maine to Wisconsin, also following the Alleghanies southward
to Georgia and Alabama.
=17. Hemlock= (_Tsuga mertensiana_). Large-sized tree, wood claimed to
be heavier and harder than the Eastern species and of superior
quality. Used for pulp wood, floors, panels, and newels. It is not
suitable for heavy construction, especially where exposed to the
weather, it is straight in grain and will take a good polish. Not
adapted for use partly in and partly out of the ground; in fresh water
as piles will last about ten years, but as it is softer than fir it is
less able to stand driving successfully. Washington to California and
eastward to Montana.
LARCH or TAMARACK
Wood like the best of hard pine both in appearance, quality, and uses,
and owing to its great durability somewhat preferred in shipbuilding,
for telegraph poles, and railway ties. In its structure it resembles
spruce. The larches are deciduous trees, occasionally covering
considerable areas, but usually scattered among other conifers.
=18. Tamarack= (_Larix laricina_ var. _Americana_) (Larch, Black Larch,
American Larch, Hacmatac). Heartwood light brown in color, sapwood
nearly white, coarse conspicuous grain, compact structure, annual
rings pronounced. Wood heavy, hard, very strong, durable in contact
with the soil. Used for railway ties, fence posts, sills, ship
timbers, telegraph poles, flagstaffs. Medium-sized tree, often
covering swamps, in which case it is smaller and of poor quality.
Maine to Minnesota, and southward to Pennsylvania.
=19. Tamarack= (_Larix occidentalis_) (Western Larch, Larch).
Large-sized trees, scattered, locally abundant. Is little inferior to
oak in strength and durability. Heartwood of a light brown color with
lighter sapwood, has a fine, slightly satiny grain, and is fairly free
from knots; the annual rings are distant. Used for railway ties and
shipbuilding. Washington and Oregon to Montana.
PINE
Very variable, very light and soft in "soft" pine, such as white pine;
of medium weight to heavy and quite hard in "hard" pine, of which the
long-leaf or Georgia pine is the extreme form. Usually it is stiff,
quite strong, of even texture, and more or less resinous. The sapwood
is yellowish white; the heartwood orange brown. Pine shrinks
moderately, seasons rapidly and without much injury; it works easily,
is never too hard to nail (unlike oak or hickory); it is mostly quite
durable when in contact with the soil, and if well seasoned is not
subject to the attacks of boring insects. The heavier the wood, the
darker, stronger, and harder it is, and the more it shrinks and checks
when seasoning. Pine is used more extensively than any other wood. It
is the principal wood in carpentry, as well as in all heavy
construction, bridges, trestles, etc. It is also used in almost every
other wood industry; for spars, masts, planks, and timbers in
shipbuilding, in car and wagon construction, in cooperage and
woodenware; for crates and boxes, in furniture work, for toys and
patterns, water pipes, excelsior, etc. Pines are usually large-sized
trees with few branches, the straight, cylindrical, useful stem
forming by far the greatest part of the tree. They occur gregariously,
forming vast forests, a fact which greatly facilitates their
exploitation. Of the many special terms applied to pine as lumber,
denoting sometimes differences in quality, the following deserve
attention: "White pine," "pumpkin pine," "soft pine," in the Eastern
markets refer to the wood of the white pine (_Pinus strobus_), and on
the Pacific Coast to that of the sugar pine (_Pinus lambertiana_).
"Yellow pine" is applied in the trade to all the Southern lumber
pines; in the Northwest it is also applied to the pitch pine (_Pinus
regida_); in the West it refers mostly to the bull pine (_Pinus
ponderosa_). "Yellow long-leaf pine" (Georgia pine), chiefly used in
advertisements, refers to the long-leaf Pine (_Pinus palustris_).
(_a_) Soft Pines
=20. White Pine= (_Pinus strobus_) (Soft Pine, Pumpkin Pine, Weymouth
Pine, Yellow Deal). Large to very large-sized tree, reaching a height
of 80 to 100 feet or more, and in some instances 7 or 8 feet in
diameter. For the last fifty years the most important timber tree of
the United States, furnishing the best quality of soft pine. Heartwood
cream white; sapwood nearly white. Close straight grain, compact
structure; comparatively free from knots and resin. Soft, uniform;
seasons well; easy to work; nails without splitting; fairly durable in
contact with the soil; and shrinks less than other species of pine.
Paints well. Used for carpentry, construction, building, spars, masts,
matches, boxes, etc., etc., etc.
=21. Sugar Pine= (_Pinus lambertiana_) (White Pine, Pumpkin Pine, Soft
Pine). A very large tree, forming extensive forests in the Rocky
Mountains and furnishing most of the timber of the western United
States. It is confined to Oregon and California, and grows at from
1,500 to 8,000 feet above sea level. Has an average height of 150 to
175 feet and a diameter of 4 to 5 feet, with a maximum height of 235
feet and 12 feet in diameter. The wood is soft, durable,
straight-grained, easily worked, very resinous, and has a satiny
luster which makes it appreciated for interior work. It is extensively
used for doors, blinds, sashes, and interior finish, also for
druggists' drawers, owing to its freedom from odor, for oars,
mouldings, shipbuilding, cooperage, shingles, and fruit boxes. Oregon
and California.
=22. White Pine= (_Pinus monticolo_). A large tree, at home in Montana,
Idaho, and the Pacific States. Most common and locally used in
northern Idaho.
=23. White Pine= (_Pinus flexilis_). A small-sized tree, forming
mountain forests of considerable extent and locally used. Eastern
Rocky Mountain slopes, Montana to New Mexico.
(_b_) Hard Pines
=24. Long-Leaf Pine= (_Pinus palustris_) (Georgia Pine, Southern Pine,
Yellow Pine, Southern Hard Pine, Long-straw Pine, etc.). Large-sized
tree. This species furnishes the hardest and most durable as well as
one of the strongest pine timbers in the market. Heartwood orange,
sapwood lighter color, the annual rings are strongly marked, and it is
full of resinous matter, making it very durable, but difficult to
work. It is hard, dense, and strong, fairly free from knots,
straight-grained, and one of the best timbers for heavy engineering
work where great strength, long span, and durability are required.
Used for heavy construction, shipbuilding, cars, docks, beams, ties,
flooring, and interior decoration. Coast region from North Carolina to
Texas.
=25. Bull Pine= (_Pinus ponderosa_) (Yellow Pine, Western Yellow Pine,
Western Pine, Western White Pine, California White Pine). Medium- to
very large-sized tree, forming extensive forests in the Pacific and
Rocky Mountain regions. Heartwood reddish brown, sapwood yellowish
white, and there is often a good deal of it. The resinous smell of the
wood is very remarkable. It is extensively used for beams, flooring,
ceilings, and building work generally.
=26. Bull Pine= (_Pinus Jeffreyi_) (Black Pine). Large-sized tree, wood
resembles _Pinus ponderosa_ and replacing same at high altitudes. Used
locally in California.
=27. Loblolly Pine= (_Pinus tæda_) (Slash Pine, Old Field Pine, Rosemary
Pine, Sap Pine, Short-straw Pine). A large-sized tree, forms extensive
forests. Wider-ringed, coarser, lighter, softer, with more sapwood
than the long-leaf pine, but the two are often confounded in the
market. The more Northern tree produces lumber which is weak, brittle,
coarse-grained, and not durable, the Southern tree produces a better
quality wood. Both are very resinous. This is the common lumber pine
from Virginia to South Carolina, and is found extensively in Arkansas
and Texas. Southern States, Virginia to Texas and Arkansas.
=28. Norway Pine= (_Pinus resinosa_) (American Red Pine, Canadian Pine).
Large-sized tree, never forming forests, usually scattered or in
small groves, together with white pine. Largely sapwood and hence not
durable. Heartwood reddish white, with fine, clear grain, fairly tough
and elastic, not liable to warp and split. Used for building
construction, bridges, piles, masts, and spars. Minnesota to Michigan;
also in New England to Pennsylvania.
=29. Short-Leaf Pine= (_Pinus echinata_) (Slash Pine, Spruce Pine,
Carolina Pine, Yellow Pine, Old Field Pine, Hard Pine). A medium- to
large-sized tree, resembling loblolly pine, often approaches in its
wood the Norway pine. Heartwood orange, sapwood lighter; compact
structure, apt to be variable in appearance in cross-section. Wood
usually hard, tough, strong, durable, resinous. A valuable timber
tree, sometimes worked for turpentine. Used for heavy construction,
shipbuilding, cars, docks, beams, ties, flooring, and house trim.
_Pinus echinata_, _palustris_, and _tæda_ are very similar in
character, of thin wood and very difficult to distinguish one from
another. As a rule, however, _palustris_ (Long-leaf Pine) has the
smallest and most uniform growth rings, and _Pinus tæda_ (Loblolly
Pine) has the largest. All are apt to be bunched together in the
lumber market as Southern Hard Pine. All are used for the same
purposes. Short-leaf is the common lumber pine of Missouri and
Arkansas. North Carolina to Texas and Missouri.
=30. Cuban Pine= (_Pinus cubensis_) (Slash Pine, Swamp Pine, Bastard
Pine, Meadow Pine). Resembles long-leaf pine, but commonly has a wider
sapwood and coarser grain. Does not enter the markets to any extent.
Along the coast from South Carolina to Louisiana.
=31. Pitch Pine= (_Pinus rigida_) (Torch Pine). A small to medium-sized
tree. Heartwood light brown or red, sapwood yellowish white. Wood
light, soft, not strong, coarse-grained, durable, very resinous. Used
locally for lumber, fuel, and charcoal. Coast regions from New York
to Georgia, and along the mountains to Kentucky.
=32. Black Pine= (_Pinus murryana_) (Lodge-pole Pine, Tamarack).
Small-sized tree. Rocky Mountains and Pacific regions.
=33. Jersey Pine= (_Pinus inops_ var. _Virginiana_) (Scrub Pine).
Small-sized tree. Along the coast from New York to Georgia and along
the mountains to Kentucky.
=34. Gray Pine= (_Pinus divaricata_ var. _banksiana_) (Scrub Pine, Jack
Pine). Medium- to large-sized tree. Heartwood pale brown, rarely
yellow; sapwood nearly white. Wood light, soft, not strong,
close-grained. Used for fuel, railway ties, and fence posts. In days
gone by the Indians preferred this species for frames of canoes.
Maine, Vermont, and Michigan to Minnesota.
REDWOOD (See Cedar)
SPRUCE
Resembles soft pine, is light, very soft, stiff, moderately strong,
less resinous than pine; has no distinct heartwood, and is of whitish
color. Used like soft pine, but also employed as resonance wood in
musical instruments and preferred for paper pulp. Spruces, like pines,
form extensive forests. They are more frugal, thrive on thinner soils,
and bear more shade, but usually require a more humid climate. "Black"
and "White" spruce as applied by lumbermen usually refer to narrow and
wide-ringed forms of black spruce (_Picea nigra_).
=35. Black Spruce= (_Picea nigra_ var. _mariana_). Medium-sized tree,
forms extensive forests in northwestern United States and in British
America; occurs scattered or in groves, especially in low lands
throughout the northern pineries. Important lumber tree in eastern
United States. Heartwood pale, often with reddish tinge; sapwood pure
white. Wood light, soft, not strong. Chiefly used for manufacture of
paper pulp, and great quantities of this as well as _Picea alba_ are
used for this purpose. Used also for sounding boards for pianos,
violins, etc. Maine to Minnesota, British America, and in the
Alleghanies to North Carolina.
=36. White Spruce= (_Picea canadensis_ var. _alba_). Medium- to
large-sized tree. Heartwood light yellow; sapwood nearly white.
Generally associated with the preceding. Most abundant along streams
and lakes, grows largest in Montana and forms the most important tree
of the sub-arctic forest of British America. Used largely for floors,
joists, doors, sashes, mouldings, and panel work, rapidly superceding
_Pinus strobus_ for building purposes. It is very similar to Norway
pine, excels it in toughness, is rather less durable and dense, and
more liable to warp in seasoning. Northern United States from Maine to
Minnesota, also from Montana to Pacific, British America.
=37. White Spruce= (_Picea engelmanni_). Medium- to large-sized tree,
forming extensive forests at elevations from 5,000 to 10,000 feet
above sea level; resembles the preceding, but occupies a different
station. A very important timber tree in the central and southern
parts of the Rocky Mountains. Rocky Mountains from Mexico to Montana.
=38. Tide-Land Spruce= (_Picea sitchensis_) (Sitka Spruce). A
large-sized tree, forming an extensive coast-belt forest. Used
extensively for all classes of cooperage and woodenware on the Pacific
Coast. Along the sea-coast from Alaska to central California.
=39. Red Spruce= (_Picea rubens_). Medium-sized tree, generally
associated with _Picea nigra_ and occurs scattered throughout the
northern pineries. Heartwood reddish; sapwood lighter color,
straight-grained, compact structure. Wood light, soft, not strong,
elastic, resonant, not durable when exposed. Used for flooring,
carpentry, shipbuilding, piles, posts, railway ties, paddles, oars,
sounding boards, paper pulp, and musical instruments. Montana to
Pacific, British America.
BASTARD SPRUCE
Spruce or fir in name, but resembling hard pine or larch in
appearance, quality and uses of its wood.
=40. Douglas Spruce= (_Pseudotsuga douglasii_) (Yellow Fir, Red Fir,
Oregon Pine). One of the most important trees of the western United
States; grows very large in the Pacific States, to fair size in all
parts of the mountains, in Colorado up to about 10,000 feet above sea
level; forms extensive forests, often of pure growth, it is really
neither a pine nor a fir. Wood very variable, usually coarse-grained
and heavy, with very pronounced summer-wood. Hard and strong ("red"
fir), but often fine-grained and light ("yellow" fir). It is the chief
tree of Washington and Oregon, and most abundant and most valuable in
British Columbia, where it attains its greatest size. From the plains
to the Pacific Ocean, and from Mexico to British Columbia.
=41. Red Fir= (_Pseudotsuga taxifolia_) (Oregon Pine, Puget Sound Pine,
Yellow Fir, Douglas Spruce, Red Pine). Heartwood light red or yellow
in color, sapwood narrow, nearly white, comparatively free from
resins, variable annual rings. Wood usually hard, strong, difficult to
work, durable, splinters easily. Used for heavy construction,
dimension timber, railway ties, doors, blinds, interior finish, piles,
etc. One of the most important of Western trees. From the plains to
the Pacific Ocean, and from Mexico to British America.
TAMARACK (See Larch)
YEW
Wood heavy, hard, extremely stiff and strong, of fine texture with a
pale yellow sapwood, and an orange-red heartwood; seasons well and is
quite durable. Extensively used for archery bows, turner's ware, etc.
The yews form no forests, but occur scattered with other conifers.
=42. Yew= (_Taxus brevifolia_). A small to medium-sized tree of the
Pacific region.
SECTION III
BROAD-LEAVED TREES
WOOD OF BROAD-LEAVED TREES
[Illustration: Fig. 4. Block of Oak. CS, cross-section; RS,
radial section; TS, tangential section; _mr_, medullary or
pith ray; _a_, height; _b_, width; and _e_, length of pith
ray.]
[Illustration: Fig. 5. Board of Oak. CS, cross-section; RS,
radial section; TS, tangential section; _v_, vessels or
pores, cut through.; A, slight curve in log which appears in
section as an islet.]
[Illustration: Fig. 6. Cross-section of Oak (Magnified about
5 times).]
On a cross-section of oak, the same arrangement of pith and bark, of
sapwood and heartwood, and the same disposition of the wood in
well-defined concentric or annual rings occur, but the rings are
marked by lines or rows of conspicuous pores or openings, which occupy
the greater part of the spring-wood for each ring (see Fig. 4, also
6), and are, in fact the hollows of vessels through which the cut has
been made. On the radial section or quarter-sawn board the several
layers appear as so many stripes (see Fig. 5); on the tangential
section or "bastard" face patterns similar to those mentioned for pine
wood are observed. But while the patterns in hard pine are marked by
the darker summer-wood, and are composed of plain, alternating stripes
of darker and lighter wood, the figures in oak (and other broad-leaved
woods) are due chiefly to the vessels, those of the spring-wood in oak
being the most conspicuous (see Fig. 5). So that in an oak table, the
darker, shaded parts are the spring-wood, the lighter unicolored parts
the summer-wood. On closer examination of the smooth cross-section of
oak, the spring-wood part of the ring is found to be formed in great
part of pores; large, round, or oval openings made by the cut through
long vessels. These are separated by a grayish and quite porous
tissue (see Fig. 6, A), which continues here and there in the form of
radial, often branched, patches (not the pith rays) into and through
the summer-wood to the spring-wood of the next ring. The large vessels
of the spring-wood, occupying six to ten per cent of the volume of a
log in very good oak, and twenty-five per cent or more in inferior and
narrow-ringed timber, are a very important feature, since it is
evident that the greater their share in the volume, the lighter and
weaker the wood. They are smallest near the pith, and grow wider
outward. They are wider in the stem than limb, and seem to be of
indefinite length, forming open channels, in some cases probably as
long as the tree itself. Scattered through the radiating gray patches
of porous wood are vessels similar to those of the spring-wood, but
decidedly smaller. These vessels are usually fewer and larger near the
outer portions of the ring. Their number and size can be utilized to
distinguish the oaks classed as white oaks from those classed as black
and red oaks. They are fewer and larger in red oaks, smaller but much
more numerous in white oaks. The summer-wood, except for these radial,
grayish patches, is dark colored and firm. This firm portion, divided
into bodies or strands by these patches of porous wood, and also by
fine, wavy, concentric lines of short, thin-walled cells (see Fig. 6,
A), consists of thin-walled fibres (see Fig. 7, B), and is the chief
element of strength in oak wood. In good white oak it forms one-half
or more of the wood, if it cuts like horn, and the cut surface is
shiny, and of a deep chocolate brown color. In very narrow-ringed wood
and in inferior red oak it is usually much reduced in quantity as well
as quality. The pith rays of the oak, unlike those of the coniferous
woods, are at least in part very large and conspicuous. (See Fig. 4;
their height indicated by the letter _a_, and their width by the
letter _b_.) The large medullary rays of oak are often twenty and more
cells wide, and several hundred cell rows in height, which amount
commonly to one or more inches. These large rays are conspicuous on
all sections. They appear as long, sharp, grayish lines on the
cross-sections; as short, thick lines, tapering at each end, on the
tangential or "bastard" face, and as broad, shiny bands, "the
mirrors," on the radial section. In addition to these coarse rays,
there is also a large number of small pith rays, which can be seen
only when magnified. On the whole, the pith rays form a much larger
part of the wood than might be supposed. In specimens of good white
oak it has been found that they form about sixteen to twenty-five per
cent of the wood.
[Illustration: Fig. 7. Portion of the Firm Bodies of Fibres
with Two Cells of a Small Pith Ray _mr_ (Highly Magnified).]
[Illustration: Fig. 8. Isolated Fibres and Cells, _a_, four
cells of wood, parenchyma; _b_, two cells from a pith ray;
_c_, a single joint or cell of a vessel, the openings _x_
leading into its upper and lower neighbors; _d_, tracheid;
_e_, wood fibre proper.]
Minute Structure
[Illustration: Fig. 9. Cross-section of Basswood (Magnified).
_v_, vessels; _mr_, pith rays.]
If a well-smoothed thin disk or cross-section of oak (say
one-sixteenth inch thick) is held up to the light, it looks very much
like a sieve, the pores or vessels appearing as clean-cut holes. The
spring-wood and gray patches are seen to be quite porous, but the firm
bodies of fibres between them are dense and opaque. Examined with a
magnifier it will be noticed that there is no such regularity of
arrangement in straight rows as is conspicuous in pine. On the
contrary, great irregularity prevails. At the same time, while the
pores are as large as pin holes, the cells of the denser wood, unlike
those of pine wood, are too small to be distinguished. Studied with
the microscope, each vessel is found to be a vertical row of a great
number of short, wide tubes, joined end to end (see Fig. 8, _c_). The
porous spring-wood and radial gray tracts are partly composed of
smaller vessels, but chiefly of tracheids, like those of pine, and of
shorter cells, the "wood parenchyma," resembling the cells of the
medullary rays. These latter, as well as the fine concentric lines
mentioned as occurring in the summer-wood, are composed entirely of
short tube-like parenchyma cells, with square or oblique ends (see
Fig. 8, _a_ and _b_). The wood fibres proper, which form the dark,
firm bodies referred to, are very fine, thread-like cells, one
twenty-fifth to one-tenth inch long, with a wall commonly so thick
that scarcely any empty internal space or lumen remains (see Figs. 8,
_e_, and 7, B). If, instead of oak, a piece of poplar or basswood (see
Fig. 9) had been used in this study, the structure would have been
found to be quite different. The same kinds of cell-elements, vessels,
etc., are, to be sure, present, but their combination and arrangement
are different, and thus from the great variety of possible
combinations results the great variety of structure and, in
consequence, of the qualities which distinguish the wood of
broad-leaved trees. The sharp distinction of sap wood and heartwood is
wanting; the rings are not so clearly defined; the vessels of the
wood are small, very numerous, and rather evenly scattered through the
wood of the annual rings, so that the distinction of the ring almost
vanishes and the medullary or pith rays in poplar can be seen, without
being magnified, only on the radial section.
LIST OF MOST IMPORTANT BROAD-LEAVED TREES (HARDWOODS)
Woods of complex and very variable structure, and therefore differing
widely in quality, behavior, and consequently in applicability to the
arts.
AILANTHUS
=1. Ailanthus= (_Ailanthus glandulosa_). Medium to large-sized tree.
Wood pale yellow, hard, fine-grained, and satiny. This species
originally came from China, where it is known as the Tree of "Heaven,"
was introduced into the United States and planted near Philadelphia
during the 18th century, and is more ornamental than useful. It is
used to some extent in cabinet work. Western Pennsylvania and Long
Island, New York.
ASH
Wood heavy, hard, stiff, quite tough, not durable in contact with the
soil, straight-grained, rough on the split surfaces and coarse in
texture. The wood shrinks moderately, seasons with little injury,
stands well, and takes a good polish. In carpentry, ash is used for
stairways, panels, etc. It is used in shipbuilding, in the
construction of cars, wagons, etc., in the manufacture of all kinds of
farm implements, machinery, and especially of all kinds of furniture;
for cooperage, baskets, oars, tool handles, hoops, etc., etc. The
trees of the several species of ash are rapid growers, of small to
medium height with stout trunks. They form no forests, but occur
scattered in almost all our broad-leaved forests.
=2. White Ash= (_Fraxinus Americana_). Medium-, sometimes large-sized
tree. Heartwood reddish brown, usually mottled; sapwood lighter color,
nearly white. Wood heavy, hard, tough, elastic, coarse-grained,
compact structure. Annual rings clearly marked by large open pores,
not durable in contact with the soil, is straight-grained, and the
best material for oars, etc. Used for agricultural implements, tool
handles, automobile (rim boards), vehicle bodies and parts, baseball
bats, interior finish, cabinet work, etc., etc. Basin of the Ohio, but
found from Maine to Minnesota and Texas.
=3. Red Ash= (_Fraxinus pubescens_ var. _Pennsylvanica_). Medium-sized
tree, a timber very similar to, but smaller than _Fraxinus Americana_.
Heartwood light brown, sapwood lighter color. Wood heavy, hard,
strong, and coarse-grained. Ranges from New Brunswick to Florida, and
westward to Dakota, Nebraska, and Kansas.
=4. Black Ash= (_Fraxinus nigra_ var. _sambucifolia_) (Hoop Ash, Ground
Ash). Medium-sized tree, very common, is more widely distributed than
the _Fraxinus Americana_; the wood is not so hard, but is well suited
for hoops and basketwork. Heartwood dark brown, sapwood light brown or
white. Wood heavy, rather soft, tough and coarse-grained. Used for
barrel hoops, basketwork, cabinetwork and interior of houses. Maine to
Minnesota and southward to Alabama.
=5. Blue Ash= (_Fraxinus quadrangulata_). Small to medium-sized tree.
Heartwood yellow, streaked with brown, sapwood a lighter color. Wood
heavy, hard, and coarse-grained. Not common. Indiana and Illinois;
occurs from Michigan to Minnesota and southward to Alabama.
=6. Green Ash= (_Fraxinus viridis_). Small-sized tree. Occurs from New
York to the Rocky Mountains, and southward to Florida and Arizona.
=7. Oregon Ash= (_Fraxinus Oregana_). Small to medium-sized tree. Occurs
from western Washington to California.
=8. Carolina Ash= (_Fraxinus Caroliniana_). Medium-sized tree. Occurs in
the Carolinas and the coast regions southward.
ASPEN (See Poplar)
BASSWOOD
=9. Basswood= (_Tilia Americana_) (Linden, Lime Tree, American Linden,
Lin, Bee Tree). Medium- to large-sized tree. Wood light, soft, stiff,
but not strong, of fine texture, straight and close-grained, and white
to light brown color, but not durable in contact with the soil. The
wood shrinks considerably in drying, works well and stands well in
interior work. It is used for cooperage, in carpentry, in the
manufacture of furniture and woodenware (both turned and carved), for
toys, also for panelling of car and carriage bodies, for agricultural
implements, automobiles, sides and backs of drawers, cigar boxes,
excelsior, refrigerators, trunks, and paper pulp. It is also largely
cut for veneer and used as "three-ply" for boxes and chair seats. It
is used for sounding boards in pianos and organs. If well seasoned and
painted it stands fairly well for outside work. Common in all northern
broad-leaved forests. Found throughout the eastern United States, but
reaches its greatest size in the Valley of the Ohio, becoming often
130 feet in height, but its usual height is about 70 feet.
=10. White Basswood= (_Tilia heterophylla_) (Whitewood). A small-sized
tree. Wood in its quality and uses similar to the preceding, only it
is lighter in color. Most abundant in the Alleghany region.
=11. White Basswood= (_Tilia pubescens_) (Downy Linden, Small-leaved
Basswood). Small-sized tree. Wood in its quality and uses similar to
_Tilia Americana_. This is a Southern species which makes it way as
far north as Long Island. Is found at its best in South Carolina.
BEECH
=12. Beech= (_Fagus ferruginea_) (Red Beech, White Beech). Medium-sized
tree, common, sometimes forming forests of pure growth. Wood heavy,
hard, stiff, strong, of rather coarse texture, white to light brown
color, not durable in contact with the soil, and subject to the
inroads of boring insects. Rather close-grained, conspicuous medullary
rays, and when quarter-sawn and well smoothed is very beautiful. The
wood shrinks and checks considerably in drying, works well and stands
well, and takes a fine polish. Beech is comparatively free from
objectionable taste, and finds a place in the manufacture of
commodities which come in contact with foodstuffs, such as lard tubs,
butter boxes and pails, and the beaters of ice cream freezers; for the
latter the persistent hardness of the wood when subjected to attrition
and abrasion, while wet gives it peculiar fitness. It is an excellent
material for churns. Sugar hogsheads are made of beech, partly because
it is a tasteless wood and partly because it has great strength. A
large class of woodenware, including veneer plates, dishes, boxes,
paddles, scoops, spoons, and beaters, which belong to the kitchen and
pantry, are made of this species of wood. Beech picnic plates are made
by the million, a single machine turning out 75,000 a day. The wood
has a long list of miscellaneous uses and enters in a great variety of
commodities. In every region where it grows in commercial quantities
it is made into boxes, baskets, and crating. Beech baskets are chiefly
employed in shipping fruit, berries, and vegetables. In Maine thin
veneer of beech is made specially for the Sicily orange and lemon
trade. This is shipped in bulk and the boxes are made abroad. Beech is
also an important handle wood, although not in the same class with
hickory. It is not selected because of toughness and resiliency, as
hickory is, and generally goes into plane, handsaw, pail, chisel, and
flatiron handles. Recent statistics show that in the production of
slack cooperage staves, only two woods, red gum and pine, stood above
beech in quantity, while for heading, pine alone exceeded it. It is
also used in turnery, for shoe lasts, butcher blocks, ladder rounds,
etc. Abroad it is very extensively used by the carpenter, millwright,
and wagon maker, in turnery and wood carving. Most abundant in the
Ohio and Mississippi basin, but found from Maine to Wisconsin and
southward to Florida.
BIRCH
=13. Cherry Birch= (_Betula lenta_) (Black Birch, Sweet Birch, Mahogany
Birch, Wintergreen Birch). Medium-sized tree, very common. Wood of
beautiful reddish or yellowish brown, and much of it nicely figured,
of compact structure, is straight in grain, heavy, hard, strong, takes
a fine polish, and considerably used as imitation of mahogany. The
wood shrinks considerably in drying, works well and stands well, but
is not durable in contact with the soil. The medullary rays in birch
are very fine and close and not easily seen. The sweet birch is very
handsome, with satiny luster, equalling cherry, and is too costly a
wood to be profitably used for ordinary purposes, but there are both
high and low grades of birch, the latter consisting chiefly of sapwood
and pieces too knotty for first class commodities. This cheap material
swells the supply of box lumber, and a little of it is found wherever
birch passes through sawmills. The frequent objections against sweet
birch as box lumber and crating material are that it is hard to nail
and is inclined to split. It is also used for veneer picnic plates and
butter dishes, although it is not as popular for this class of
commodity as are yellow and paper birch, maple and beech. The best
grades are largely used for furniture and cabinet work, and also for
interior finish. Maine to Michigan and to Tennessee.
=14. White Birch= (_Betula populifolia_) (Gray Birch, Old Field Birch,
Aspen-leaved Birch). Small to medium-sized tree, least common of all
the birches. Short-lived, twenty to thirty feet high, grows very
rapidly. Heartwood light brown, sapwood lighter color. Wood light,
soft, close-grained, not strong, checks badly in drying, decays
quickly, not durable in contact with the soil, takes a good polish.
Used for spools, shoepegs, wood pulp, and barrel hoops. Fuel, value
not high, but burns with bright flame. Ranges from Nova Scotia and
lower St. Lawrence River, southward, mostly in the coast region to
Delaware, and westward through northern New England and New York to
southern shore of Lake Ontario.
=15. Yellow Birch= (_Betula lutea_) (Gray Birch, Silver Birch). Medium-
to large-sized tree, very common. Heartwood light reddish brown,
sapwood nearly white, close-grained, compact structure, with a satiny
luster. Wood heavy, very strong, hard, tough, susceptible of high
polish, not durable when exposed. Is similar to _Betula lenta_, and
finds a place in practically all kinds of woodenware. A large
percentage of broom handles on the market are made of this species of
wood, though nearly every other birch contributes something. It is
used for veneer plates and dishes made for pies, butter, lard, and
many other commodities. Tubs and pails are sometimes made of yellow
birch provided weight is not objectionable. The wood is twice as heavy
as some of the pines and cedars. Many small handles for such articles
as flatirons, gimlets, augers, screw drivers, chisels, varnish and
paint brushes, butcher and carving knives, etc. It is also widely used
for shipping boxes, baskets, and crates, and it is one of the
stiffest, strongest woods procurable, but on account of its excessive
weight it is sometimes discriminated against. It is excellent for
veneer boxes, and that is probably one of the most important places it
fills. Citrus fruit from northern Africa and the islands and countries
of the Mediterranean is often shipped to market in boxes made of
yellow birch from veneer cut in New England. The better grades are
also used for furniture and cabinet work, and the "burls" found on
this species are highly valued for making fancy articles, gavels, etc.
It is extensively used for turnery, buttons, spools, bobbins, wheel
hubs, etc. Maine to Minnesota and southward to Tennessee.
=16. Red Birch= (_Betula rubra_ var. _nigra_) (River Birch). Small to
medium-sized tree, very common. Lighter and less valuable than the
preceding. Heartwood light brown, sapwood pale. Wood light, fairly
strong and close-grained. Red birch is best developed in the middle
South, and usually grows near the banks of rivers. Its bark hangs in
tatters, even worse than that of paper birch, but it is darker. In
Tennessee the slack coopers have found that red birch makes excellent
barrel heads and it is sometimes employed in preference to other
woods. In eastern Maryland the manufacturers of peach baskets draw
their supplies from this wood, and substitute it for white elm in
making the hoops or bands which stiffen the top of the basket, and
provide a fastening for the veneer which forms the sides. Red birch
bends in a very satisfactory manner, which is an important point. This
wood enters pretty generally into the manufacture of woodenware within
its range, but statistics do not mention it by name. It is also used
in the manufacture of veneer picnic plates, pie plates, butter dishes,
washboards, small handles, kitchen and pantry utensils, and ironing
boards. New England to Texas and Missouri.
=17. Canoe Birch= (_Betula paprifera_) (White Birch, Paper Birch). Small
to medium-sized tree, sometimes forming forests, very common.
Heartwood light brown tinged with red, sapwood lighter color. Wood of
good quality, but light, fairly hard and strong, tough, close-grained.
Sap flows freely in spring and by boiling can be made into syrup. Not
as valuable as any of the preceding. Canoe birch is a northern tree,
easily identified by its white trunk and its ragged bark. Large
numbers of small wooden boxes are made by boring out blocks of this
wood, shaping them in lathes, and fitting lids on them. Canoe birch is
one of the best woods for this class of commodities, because it can be
worked very thin, does not split readily, and is of pleasing color.
Such boxes, or two-piece diminutive kegs, are used as containers for
articles shipped and sold in small bulk, such as tacks, small nails,
and brads. Such containers are generally cylindrical and of
considerably greater depth than diameter. Many others of nearly
similar form are made to contain ink bottles, bottles of perfumery,
drugs, liquids, salves, lotions, and powders of many kinds. Many boxes
of this pattern are used by manufacturers of pencils and crayons for
packing and shipping their wares. Such boxes are made in numerous
numbers by automatic machinery. A single machine of the most improved
pattern will turn out 1,400 boxes an hour. After the boring and
turning are done, they are smoothed by placing them into a tumbling
barrel with soapstone. It is also used for one-piece shallow trays or
boxes, without lids, and used as card receivers, pin receptacles,
butter boxes, fruit platters, and contribution plates in churches. It
is also the principal wood used for spools, bobbins, bowls, shoe
lasts, pegs, and turnery, and is also much used in the furniture
trade. All along the northern boundary of the United States and
northward, from the Atlantic to the Pacific.
BLACK WALNUT (See Walnut)
BLUE BEECH
=18. Blue Beech= (_Carpinus Caroliniana_) (Hornbeam, Water Beech,
Ironwood). Small-sized tree. Heartwood light brown, sapwood nearly
white. Wood very hard, heavy, strong, very stiff, of rather fine
texture, not durable in contact with the soil, shrinks and checks
considerably in drying, but works well and stands well, and takes a
fine polish. Used chiefly in turnery, for tool handles, etc. Abroad
much used by mill-and wheelwrights. A small tree, largest in the
Southwest, but found in nearly all parts of the eastern United States.
BOIS D'ARC (See Osage Orange)
BUCKEYE
Wood light, soft, not strong, often quite tough, of fine, uniform
texture and creamy white color. It shrinks considerably in drying, but
works well and stands well. Used for woodenware, artificial limbs,
paper pulp, and locally also for building construction.
=19. Ohio Buckeye= (_Æsculus glabra_) (Horse Chestnut, Fetid Buckeye).
Small-sized tree, scattered, never forming forests. Heartwood white,
sapwood pale brown. Wood light, soft, not strong, often quite tough
and close-grained. Alleghanies, Pennsylvania to Oklahoma.
=20. Sweet Buckeye= (_Æsculus octandra_ var. _flava_) (Horse Chestnut).
Small-sized tree, scattered, never forming forests. Wood in its
quality and uses similar to the preceding. Alleghanies, Pennsylvania
to Texas.
BUCKTHORNE
=21. Buckthorne= (_Rhanmus Caroliniana_) (Indian Cherry). Small-sized
tree. Heartwood light brown, sapwood almost white. Wood light, hard,
close-grained. Does not enter the markets to any great extent. Found
along the borders of streams in rich bottom lands. Its northern limits
is Long Island, where it is only a shrub; it becomes a tree only in
southern Arkansas and adjoining regions.
BUTTERNUT
=22. Butternut= (_Juglans cinerea_) (White Walnut, White Mahogany,
Walnut). Medium-sized tree, scattered, never forming forests. Wood
very similar to black walnut, but light, quite soft, and not strong.
Heartwood light gray-brown, darkening with exposure; sapwood nearly
white, coarse-grained, compact structure, easily worked, and
susceptible to high polish. Has similar grain to black walnut and when
stained is a very good imitation. Is much used for inside work, and
very durable. Used chiefly for finishing lumber, cabinet work, boat
finish and fixtures, and for furniture. Butternut furniture is often
sold as circassian walnut. Largest and most common in the Ohio basin.
Maine to Minnesota and southward to Georgia and Alabama.
CATALPA
The catalpa is a tree which was planted about 25 years ago as a
commercial speculation in Iowa, Kansas, and Nebraska. Its native
habitat was along the rivers Ohio and lower Wabash, and a century ago
it gained a reputation for rapid growth and durability, but did not
grow in large quantities. As a railway tie, experiments have left no
doubt as to its resistance to decay; it stands abrasion as well as the
white oak (_Quercus alba_), and is superior to it in longevity.
Catalpa is a tree singularly free from destructive diseases. Wood cut
from the living tree is one of the most durable timbers known. In
spite of its light porous structure it resists the weathering
influences and the attacks of wood-destroying fungi to a remarkable
degree. No fungus has yet been found which will grow in the dead
timber, and for fence posts this wood has no equal, lasting longer
than almost any other species of timber. The wood is rather soft and
coarse in texture, the tree is of slow growth, and the brown colored
heartwood, even of very young trees, forms nearly three-quarters of
their volume. There is only about one-quarter inch of sapwood in a
9-inch tree.
=23. Catalpa= (_Catalpa speciosa_ var. _bignonioides_) (Indian Bean).
Medium-sized tree. Heartwood light brown, sapwood nearly white. Wood
light, soft, not strong, brittle, very durable in contact with the
soil, of coarse texture. Used chiefly for railway ties, telegraph
poles, and fence posts, but well suited for a great variety of uses.
Lower basin of the Ohio River, locally common. Extensively planted,
and therefore promising to become of some importance.
CHERRY
=24. Cherry= (_Prunus serotina_) (Wild Cherry, Black Cherry, Rum
Cherry). Wood heavy, hard, strong, of fine texture. Sapwood yellowish
white, heartwood reddish to brown. The wood shrinks considerably in
drying, works well and stands well, has a fine satin-like luster, and
takes a fine polish which somewhat resembles mahogany, and is much
esteemed for its beauty. Cherry is chiefly used as a decorative
interior finishing lumber, for buildings, cars and boats, also for
furniture and in turnery, for musical instruments, walking sticks,
last blocks, and woodenware. It is becoming too costly for many
purposes for which it is naturally well suited. The lumber-furnishing
cherry of the United States, the wild black cherry, is a small to
medium-sized tree, scattered through many of the broad-leaved trees of
the western slope of the Alleghanies, but found from Michigan to
Florida, and west to Texas. Other species of this genus, as well as
the hawthornes (_Prunus cratoegus_) and wild apple (_Pyrus_), are not
commonly offered in the markets. Their wood is of the same character
as cherry, often finer, but in smaller dimensions.
=25. Red Cherry= (_Prunus Pennsylvanica_) (Wild Red Cherry, Bird
Cherry). Small-sized tree. Heartwood light brown, sapwood pale yellow.
Wood light, soft, and close-grained. Uses similiar to the preceding,
common throughout the Northern States, reaching its greatest size on
the mountains of Tennessee.
CHESTNUT
The chestnut is a long-lived tree, attaining an age of from 400 to 600
years, but trees over 100 years are usually hollow. It grows quickly,
and sprouts from a chestnut stump (Coppice Chestnut) often attain a
height of 8 feet in the first year. It has a fairly cylindrical stem,
and often grows to a height of 100 feet and over. Coppice chestnut,
that is, chestnut grown on an old stump, furnishes better timber for
working than chestnut grown from the nut, it is heavier, less spongy,
straighter in grain, easier to split, and stands exposure longer.
=26. Chestnut= (_Castanea vulgaris_ var. _Americana_). Medium-to
large-sized tree, never forming forests. Wood is light, moderately
hard, stiff, elastic, not strong, but very durable when in contact
with the soil, of coarse texture. Sapwood light, heartwood darker
brown, and is readily distinguishable from the sapwood, which very
early turns into heartwood. It shrinks and checks considerably in
drying, works easily, stands well. The annual rings are very distinct,
medullary rays very minute and not visible to the naked eye. Used in
cooperage, for cabinetwork, agricultural implements, railway ties,
telegraph poles, fence posts, sills, boxes, crates, coffins,
furniture, fixtures, foundation for veneer, and locally in heavy
construction. Very common in the Alleghanies. Occurs from Maine to
Michigan and southward to Alabama.
=27. Chestnut= (_Castanea dentata_ var. _vesca_). Medium-sized tree,
never forming forests, not common. Heartwood brown color, sapwood
lighter shade, coarse-grained. Wood and uses similar to the preceding.
Occurs scattered along the St. Lawrence River, and even there is met
with only in small quantities.
=28. Chinquapin= (_Castanea pumila_). Medium- to small-sized tree, with
wood slightly heavier, but otherwise similiar to the preceding. Most
common in Arkansas, but with nearly the same range as _Castanea
vulgaris_.
=29. Chinquapin= (_Castanea chrysophylla_). A medium-sized tree of the
western ranges of California and Oregon.
COFFEE TREE
=30. Coffee Tree= (_Gymnocladus dioicus_) (Coffee Nut, Stump Tree). A
medium- to large-sized tree, not common. Wood heavy, hard, strong,
very stiff, of coarse texture, and durable. Sapwood yellow, heartwood
reddish brown, shrinks and checks considerably in drying, works well
and stands well, and takes a fine polish. It is used to a limited
extent in cabinetwork and interior finish. Pennsylvania to Minnesota
and Arkansas.
COTTONWOOD (See Poplar)
CRAB APPLE
=31. Crab Apple= (_Pyrus coronaria_) (Wild Apple, Fragrant Crab).
Small-sized tree. Heartwood reddish brown, sapwood yellow. Wood heavy,
hard, not strong, close-grained. Used principally for tool handles and
small domestic articles. Most abundant in the middle and western
states, reaches its greatest size in the valleys of the lower Ohio
basin.
CUCUMBER TREE (See Magnolia)
DOGWOOD
=32. Dogwood= (_Cornus florida_) (American Box). Small to medium-sized
tree. Attains a height of about 30 feet and about 12 inches in
diameter. The heartwood is a red or pinkish color, the sapwood, which
is considerable, is a creamy white. The wood has a dull surface and
very fine grain. It is valuable for turnery, tool handles, and
mallets, and being so free from silex, watchmakers use small splinters
of it for cleaning out the pivot holes of watches, and opticians for
removing dust from deep-seated lenses. It is also used for butchers'
skewers, and shuttle blocks and wheel stock, and is suitable for
turnery and inlaid work. Occurs scattered in all the broad-leaved
forests of our country; very common.
ELM
Wood heavy, hard, strong, elastic, very tough, moderately durable in
contact with the soil, commonly cross-grained, difficult to split and
shape, warps and checks considerably in drying, but stands well if
properly seasoned. The broad sapwood whitish, heartwood light brown,
both with shades of gray and red. On split surfaces rough, texture
coarse to fine, capable of high polish. Elm for years has been the
principal wood used in slack cooperage for barrel staves, also in the
construction of cars, wagons, etc., in boat building, agricultural
implements and machinery, in saddlery and harness work, and
particularly in the manufacture of all kinds of furniture, where the
beautiful figures, especially those of the tangential or bastard
section, are just beginning to be appreciated. The elms are medium- to
large-sized trees, of fairly rapid growth, with stout trunks; they
form no forests of pure growth, but are found scattered in all the
broad-leaved woods of our country, sometimes forming a considerable
portion of the arborescent growth.
=33. White Elm= (_Ulmus Americana_) (American Elm, Water Elm). Medium-
to large-sized tree. Wood in its quality and uses as stated above.
Common. Maine to Minnesota, southward to Florida and Texas.
=34. Rock Elm= (_Ulmus racemosa_) (Cork Elm, Hickory Elm, White Elm,
Cliff Elm). Medium- to large-sized tree of rapid growth. Heartwood
light brown, often tinged with red, sapwood yellowish or greenish
white, compact structure, fibres interlaced. Wood heavy, hard, very
tough, strong, elastic, difficult to split, takes a fine polish. Used
for agricultural implements, automobiles, crating, boxes, cooperage,
tool handles, wheel stock, bridge timbers, sills, interior finish,
and maul heads. Fairly free from knots and has only a small quantity
of sapwood. Michigan, Ohio, from Vermont to Iowa, and southward to
Kentucky.
=35. Red Elm= (_Ulmus fulva_ var. _pubescens_) (Slippery Elm, Moose
Elm). The red or slippery elm is not as large a tree as the white elm
(_Ulmus Americana_), though it occasionally attains a height of 135
feet and a diameter of 4 feet. It grows tall and straight, and thrives
in river valleys. The wood is heavy, hard, strong, tough, elastic,
commonly cross-grained, moderately durable in contact with the soil,
splits easily when green, works fairly well, and stands well if
properly handled. Careful seasoning and handling are essential for the
best results. Trees can be utilized for posts when very small. When
green the wood rots very quickly in contact with the soil. Poles for
posts should be cut in summer and peeled and dried before setting. The
wood becomes very tough and pliable when steamed, and is of value for
sleigh runners and for ribs of canoes and skiffs. Together with white
elm (_Ulmus Americana_) it is extensively used for barrel staves in
slack cooperage and also for furniture. The thick, viscous inner bark,
which gives the tree its descriptive name, is quite palatable,
slightly nutritious, and has a medicinal value. Found chiefly along
water courses. New York to Minnesota, and southward to Florida and
Texas.
=36. Cedar Elm= (_Ulmus crassifolia_). Medium- to small-sized tree,
locally quite common. Arkansas and Texas.
=37. Winged Elm= (_Ulmus alata_) (Wahoo). Small-sized tree, locally
quite common. Heartwood light brown, sapwood yellowish white. Wood
heavy, hard, tough, strong, and close-grained. Arkansas, Missouri, and
eastern Virginia.
[Illustration: Fig. 10. A Large Red Gum.]
GUM
This general term applies to three important species of gum in the
South, the principal one usually being distinguished as "red" or
"sweet" gum (see Fig. 10). The next in importance being the "tupelo"
or "bay poplar," and the least of the trio is designated as "black" or
"sour" gum (see Fig. 11). Up to the year 1900 little was known of gum
as a wood for cooperage purposes, but by the continued advance in
price of the woods used, a few of the most progressive manufacturers,
looking into the future, saw that the supply of the various woods in
use was limited, that new woods would have to be sought, and gum was
looked upon as a possible substitute, owing to its cheapness and
abundant supply. No doubt in the future this wood will be used to a
considerable extent in the manufacture of both "tight" and "slack"
cooperage. In the manufacture of the gum, unless the knives and saws
are kept very sharp, the wood has a tendency to break out, the corners
splitting off; and also, much difficulty has been experienced in
seasoning and kiln-drying.
[Illustration: Fig. 11. A Tupelo Gum Slough.]
In the past, gum, having no marketable value, has been left standing
after logging operations, or, where the land has been cleared for
farming, the trees have been "girdled" and allowed to rot, and then
felled and burned as trash. Now, however, that there is a market for
this species of timber, it will be profitable to cut the gum with the
other hardwoods, and this species of wood will come in for a greater
share of attention than ever before.
=38. Red Gum= (_Liquidamber styraciflua_) (Sweet Gum, Hazel Pine, Satin
Walnut, Liquidamber, Bilsted). The wood is about as stiff and as
strong as chestnut, rather heavy, it splits easily and is quite brash,
commonly cross-grained, of fine texture, and has a large proportion of
whitish sapwood, which decays rapidly when exposed to the weather; but
the reddish brown heartwood is quite durable, even in the ground. The
external appearance of the wood is of fine grain and smooth, close
texture, but when broken the lines of fracture do not run with
apparent direction of the growth; possibly it is this unevenness of
grain which renders the wood so difficult to dry without twisting and
warping. It has little resiliency; can be easily bent when steamed,
and when properly dried will hold its shape. The annual rings are not
distinctly marked, medullary rays fine and numerous. The green wood
contains much water, and consequently is heavy and difficult to float,
but when dry it is as light as basswood. The great amount of water in
the green wood, particularly in the sap, makes it difficult to season
by ordinary methods without warping and twisting. It does not check
badly, is tasteless and odorless, and when once seasoned, swells and
shrinks but little unless exposed to the weather. Used for boat
finish, veneers, cabinet work, furniture, fixtures, interior
decoration, shingles, paving blocks, woodenware, cooperage, machinery
frames, refrigerators, and trunk slats.
Range of Red Gum
Red gum is distributed from Fairfield County, Conn., to southeastern
Missouri, through Arkansas and Oklahoma to the valley of the Trinity
River in Texas, and eastward to the Atlantic coast. Its commercial
range is restricted, however, to the moist lands of the lower Ohio and
Mississippi basins and of the Southeastern coast. It is one of the
commonest timber trees in the hardwood bottoms and drier swamps of the
South. It grows in mixture with ash, cottonwood and oak (see Fig. 12).
It is also found to a considerable extent on the lower ridges and
slopes of the southern Appalachians, but there it does not reach
merchantable value and is of little importance. Considerable
difference is found between the growth in the upper Mississippi
bottoms and that along the rivers on the Atlantic coast and on the
Gulf. In the latter regions the bottoms are lower, and consequently
more subject to floods and to continued overflows (see Fig. 11). The
alluvial deposit is also greater, and the trees grow considerably
faster. Trees of the same diameter show a larger percentage of sapwood
there than in the upper portions of the Mississippi Valley. The
Mississippi Valley hardwood trees are for the most part considerably
older, and reach larger dimensions than the timber along the coast.
Form of the Red Gum
In the best situations red gum reaches a height of 150 feet, and a
diameter of 5 feet. These dimensions, however are unusual. The stem is
straight and cylindrical, with dark, deeply-furrowed bark, and
branches often winged with corky ridges. In youth, while growing
vigorously under normal conditions, it assumes a long, regular,
conical crown, much resembling the form of a conifer (see Fig. 12).
After the tree has attained its height growth, however, the crown
becomes rounded, spreading and rather ovate in shape. When growing in
the forest the tree prunes itself readily at an early period, and
forms a good length of clear stem, but it branches strongly after
making most of its height growth. The mature tree is usually forked,
and the place where the forking commences determines the number of
logs in the tree or its merchantable length, by preventing cutting to
a small diameter in the top. On large trees the stem is often not less
than eighteen inches in diameter where the branching begins. The
over-mature tree is usually broken and dry topped, with a very
spreading crown, in consequence of new branches being sent out.
Tolerance of Red Gum
Throughout its entire life red gum is intolerant in shade, there are
practically no red seedlings under the dense forest cover of the
bottom land, and while a good many may come up under the pine forest
on the drier uplands, they seldom develop into large trees. As a rule
seedlings appear only in clearings or in open spots in the forest. It
is seldom that an over-topped tree is found, for the gum dies quickly
if suppressed, and is consequently nearly always a dominant or
intermediate tree. In a hardwood bottom forest the timber trees are
all of nearly the same age over considerable areas, and there is
little young growth to be found in the older stands. The reason for
this is the intolerance of most of the swamp species. A scale of
intolerance containing the important species, and beginning with the
most light-demanding, would run as follows: Cottonwood, sycamore, red
gum, white elm, white ash, and red maple.
Demands upon Soil and Moisture
While the red gum grows in various situations, it prefers the deep,
rich soil of the hardwood bottoms, and there reaches its best
development (see Fig. 10). It requires considerable soil moisture,
though it does not grow in the wetter swamps, and does not thrive on
dry pine land. Seedlings, however, are often found in large numbers on
the edges of the uplands and even on the sandy pine land, but they
seldom live beyond the pole stage. When they do, they form small,
scrubby trees that are of little value. Where the soil is dry the tree
has a long tap root. In the swamps, where the roots can obtain water
easily, the development of the tap root is poor, and it is only
moderate on the glade bottom lands, where there is considerable
moisture throughout the year, but no standing water in the summer
months.
Reproduction of Red Gum
[Illustration: Fig. 12. Second Growth Red Gum, Ash,
Cottonwood, and Sycamore.]
Red gum reproduces both by seed and by sprouts (see Fig. 12). It
produces seed fairly abundantly every year, but about once in three
years there is an extremely heavy production. The tree begins to bear
seed when twenty-five to thirty years old, and seeds vigorously up to
an age of one hundred and fifty years, when its productive power
begins to diminish. A great part of the seed, however, is abortive.
Red gum is not fastidious in regard to its germinating bed; it comes
up readily on sod in old fields and meadows, on decomposing humus in
the forest, or on bare clay-loam or loamy sand soil. It requires a
considerable degree of light, however, and prefers a moist seed bed.
The natural distribution of the seed takes place for several hundred
feet from the seed trees, the dissemination depending almost entirely
on the wind. A great part of the seed falls on the hardwood bottom
when the land is flooded, and is either washed away or, if already in
the ground and germinating, is destroyed by the long-continued
overflow. After germinating, the red gum seedling demands, above
everything else, abundant light for its survival and development. It
is for this reason that there is very little growth of red gum, either
in the unculled forest or on culled land, where, as is usually the
case, a dense undergrowth of cane, briers, and rattan is present.
Under the dense underbrush of cane and briers throughout much of the
virgin forest, reproduction of any of the merchantable species is of
course impossible. And even where the land has been logged over, the
forest is seldom open enough to allow reproduction of cottonwood and
red gum. Where, however, seed trees are contiguous to pastures or
cleared land, scattered seedlings are found springing up in the open,
and where openings occur in the forest, there are often large numbers
of red gum seedlings, the reproduction generally occurring in groups.
But over the greater part of the Southern hardwood bottom land forest
reproduction is very poor. The growth of red gum during the early part
of its life, and up to the time it reaches a diameter of eight inches
breast-high, is extremely rapid, and, like most of the intolerant
species, it attains its height growth at an early period. Gum sprouts
readily from the stump, and the sprouts surpass the seedlings in rate
of height growth for the first few years, but they seldom form large
timber trees. Those over fifty years of age seldom sprout. For this
reason sprout reproduction is of little importance in the forest. The
principal requirements of red gum, then, are a moist, fairly rich soil
and good exposure to light. Without these it will not reach its best
development.
[Illustration: Fig. 13. A Cypress Slough in the Dry Season.]
Second-Growth Red Gum
Second-growth red gum occurs to any considerable extent only on land
which has been thoroughly cleared. Throughout the South there is a
great deal of land which was in cultivation before the Civil War, but
which during the subsequent period of industrial depression was
abandoned and allowed to revert to forest. These old fields now mostly
covered with second-growth forest, of which red gum forms an
important part (see Fig. 12). Frequently over fifty per cent of the
stand consists of this species, but more often, and especially on the
Atlantic coast, the greater part is of cottonwood or ash. These stands
are very dense, and the growth is extremely rapid. Small stands of
young growth are also often found along the edges of cultivated
fields. In the Mississippi Valley the abandoned fields on which young
stands have sprung up are for the most part being rapidly cleared
again. The second growth here is considered of little value in
comparison with the value of the land for agricultural purposes. In
many cases, however, the farm value of the land is not at present
sufficient to make it profitable to clear it, unless the timber cut
will at least pay for the operation. There is considerable land upon
which the second growth will become valuable timber within a few
years. Such land should not be cleared until it is possible to utilize
the timber.
=39. Tupelo Gum= (_Nyssa aquatica_) (Bay Poplar, Swamp Poplar, Cotton
Gum, Hazel Pine, Circassian Walnut, Pepperidge, Nyssa). The close
similarity which exists between red and tupelo gum, together with the
fact that tupelo is often cut along with red gum, and marketed with
the sapwood of the latter, makes it not out of place to give
consideration to this timber. The wood has a fine, uniform texture, is
moderately hard and strong, is stiff, not elastic, very tough and hard
to split, but easy to work with tools. Tupelo takes glue, paint, or
varnish well, and absorbs very little of the material. In this respect
it is equal to yellow poplar and superior to cottonwood. The wood is
not durable in contact with ground, and requires much care in
seasoning. The distinction between the heartwood and sapwood of this
species is marked. The former varies in color from a dull gray to a
dull brown; the latter is whitish or light yellow like that of poplar.
The wood is of medium weight, about thirty-two pounds per cubic foot
when dry, or nearly that of red gum and loblolly pine. After
seasoning it is difficult to distinguish the better grades of sapwood
from poplar. Owing to the prejudice against tupelo gum, it was until
recently marketed under such names as bay poplar, swamp poplar, nyssa,
cotton gum, circassian walnut, and hazel pine. Since it has become
evident that the properties of the wood fit it for many uses, the
demand for tupelo has largely increased, and it is now taking rank
with other standard woods under its rightful name. Heretofore the
quality and usefulness of this wood were greatly underestimated, and
the difficulty of handling it was magnified. Poor success in seasoning
and kiln-drying was laid to defects of the wood itself, when, as a
matter of fact, the failures were largely due to the absence of proper
methods in handling. The passing of this prejudice against tupelo is
due to a better understanding of the characteristics and uses of the
wood. Handled in the way in which its particular character demands,
tupelo is a wood of much value.
Uses of Tupelo Gum
Tupelo gum is now used in slack cooperage, principally for heading. It
is used extensively for house flooring and inside finishing, such as
mouldings, door jambs, and casings. A great deal is now shipped to
European countries, where it is highly valued for different classes of
manufacture. Much of the wood is used in the manufacture of boxes,
since it works well upon rotary veneer machines. There is also an
increasing demand for tupelo for laths, wooden pumps, violin and organ
sounding boards, coffins, mantelwork, conduits and novelties. It is
also used in the furniture trade for backing, drawers, and panels.
Range of Tupelo Gum
Tupelo occurs throughout the coastal region of the Atlantic States,
from southern Virginia to northern Florida, through the Gulf States to
the valley of the Nueces River in Texas, through Arkansas and southern
Missouri to western Kentucky and Tennessee, and to the valley of the
lower Wabash River. Tupelo is being extensively milled at present only
in the region adjacent to Mobile Ala., and in southern and central
Louisiana, where it occurs in large merchantable quantities, attaining
its best development in the former locality. The country in this
locality is very swampy (see Fig. 11), and within a radius of one
hundred miles tupelo gum is one of the principal timber trees. It
grows only in the swamps and wetter situations (see Fig. 11), often in
mixture with cypress, and in the rainy season it stands in from two to
twenty feet of water.
=40. Black Gum= (_Nyssa sylvatica_) (Sour Gum). Black gum is not cut to
much extent, owing to its less abundant supply and poorer quality, but
is used for repair work on wagons, for boxes, crates, wagon hubs,
rollers, bowls, woodenware, and for cattle yokes and other purposes
which require a strong, non-splitting wood. Heartwood is light brown
in color, often nearly white; sapwood hardly distinguishable, fine
grain, fibres interwoven. Wood is heavy, not hard, difficult to work,
strong, very tough, checks and warps considerably in drying, not
durable. It is distributed from Maine to southern Ontario, through
central Michigan to southeastern Missouri, southward to the valley of
the Brazos River in Texas, and eastward to the Kissimmee River and
Tampa Bay in Florida. It is found in the swamps and hardwood bottoms,
but is more abundant and of better size on the slightly higher ridges
and hummocks in these swamps, and on the mountain slopes in the
southern Alleghany region. Though its range is greater than that of
either red or tupelo gum, it nowhere forms an important part of the
forest.
HACKBERRY
=41. Hackberry= (_Celtis occidentalis_) (Sugar Berry, Nettle Tree). The
wood is handsome, heavy, hard, strong, quite tough, of moderately fine
texture, and greenish or yellowish color, shrinks moderately, works
well and stands well, and takes a good polish. Used to some extent in
cooperage, and in the manufacture of cheap furniture. Medium- to
large-sized tree, locally quite common, largest in the lower
Mississippi Valley. Occurs in nearly all parts of the eastern United
States.
HICKORY
The hickories of commerce are exclusively North American and some of
them are large and beautiful trees of 60 to 70 feet or more in height.
They are closely allied to the walnut, and the wood is very like
walnut in grain and color, though of a somewhat darker brown. It is
one of the finest of American hardwoods in point of strength; in
toughness it is superior to ash, rather coarse in texture, smooth and
of straight grain, very heavy and strong as well as elastic and
tenacious, but decays rapidly, especially the sapwood when exposed to
damp and moisture, and is very liable to attack from worms and boring
insects. The cross-section of hickory is peculiar, the annual rings
appear like fine lines instead of like the usual pores, and the
medullary rays, which are also very fine but distinct, in crossing
these form a peculiar web-like pattern which is one of the
characteristic differences between hickory and ash. Hickory is rarely
subjected to artificial treatment, but there is this curious fact in
connection with the wood, that, contrary to most other woods, creosote
is only with difficulty injected into the sap, although there is no
difficulty in getting it into the heartwood. It dries slowly, shrinks
and checks considerably in seasoning; is not durable in contact with
the soil or if exposed. Hickory excels as wagon and carriage stock,
for hoops in cooperage, and is extensively used in the manufacture of
implements and machinery, for tool handles, timber pins, harness work,
dowel pins, golf clubs, and fishing rods. The hickories are tall trees
with slender stems, never forming forests, occasionally small groves,
but usually occur scattered among other broad-leaved trees in suitable
localities. The following species all contribute more or less to the
hickory of the markets:
=42. Shagbark Hickory= (_Hicoria ovata_) (Shellbark Hickory, Scalybark
Hickory). A medium- to large-sized tree, quite common; the favorite
among the hickories. Heartwood light brown, sapwood ivory or
cream-colored. Wood close-grained, compact structure, annual rings
clearly marked. Very hard, heavy, strong, tough, and flexible, but not
durable in contact with the soil or when exposed. Used for
agricultural implements, wheel runners, tool handles, vehicle parts,
baskets, dowel pins, harness work, golf clubs, fishing rods, etc. Best
developed in the Ohio and Mississippi basins; from Lake Ontario to
Texas, Minnesota to Florida.
=43. Mockernut Hickory= (_Hicoria alba_) (Black Nut Hickory, Black
Hickory, Bull Nut Hickory, Big Bud Hickory, White Heart Hickory). A
medium- to large-sized tree. Wood in its quality and uses similar to
the preceding. Its range is the same as that of _Hicoria ovata_.
Common, especially in the South.
=44. Pignut Hickory= (_Hicoria glabra_) (Brown Hickory, Black Hickory,
Switchbud Hickory). A medium- to large-sized tree. Heavier and
stronger than any of the preceding. Heartwood light to dark brown,
sapwood nearly white. Abundant, all eastern United States.
=45. Bitternut Hickory= (_Hicoria minima_) (Swamp Hickory). A
medium-sized tree, favoring wet localities. Heartwood light brown,
sapwood lighter color. Wood in its quality and uses not so valuable as
_Hicoria ovata_, but is used for the same purposes. Abundant, all
eastern United States.
=46. Pecan= (_Hicoria pecan_) (Illinois Nut). A large tree, very common
in the fertile bottoms of the western streams. Indiana to Nebraska and
southward to Louisiana and Texas.
HOLLY
=47. Holly= (_Ilex opaca_). Small to medium-sized tree. Wood of medium
weight, hard, strong, tough, of exceedingly fine grain, closer in
texture than most woods, of white color, sometimes almost as white as
ivory; requires great care in its treatment to preserve the whiteness
of the wood. It does not readily absorb foreign matter. Much used by
turners and for all parts of musical instruments, for handles on whips
and fancy articles, draught-boards, engraving blocks, cabinet work,
etc. The wood is often dyed black and sold as ebony; works well and
stands well. Most abundant in the lower Mississippi Valley and Gulf
States, but occurring eastward to Massachusetts and north to Indiana.
=48. Holly= (_Ilex monticolo_) (Mountain Holly). Small-sized tree. Wood
in its quality and uses similar to the preceding, but is not very
generally known. It is found in the Catskill Mountains and extends
southward along the Alleghanies as far as Alabama.
HORSE CHESTNUT (See Buckeye)
IRONWOOD
=49. Ironwood= (_Ostrya Virginiana_) (Hop Hornbeam, Lever Wood).
Small-sized tree, common. Heartwood light brown tinged with red,
sapwood nearly white. Wood heavy, tough, exceedingly close-grained,
very strong and hard, durable in contact with the soil, and will take
a fine polish. Used for small articles like levers, handles of tools,
mallets, etc. Ranges throughout the United States east of the Rocky
Mountains.
LAUREL
=50. Laurel= (_Umbellularia Californica_) (Myrtle). A Western tree,
produces timber of light brown color of great size and beauty, and is
very valuable for cabinet and inside work, as it takes a fine polish.
California and Oregon, coast range of the Sierra Nevada Mountains.
LOCUST
=51. Black Locust= (_Robinia pseudacacia_) (Locust, Yellow Locust,
Acacia). Small to medium-sized tree. Wood very heavy, hard, strong,
and tough, rivalling some of the best oak in this latter quality. The
wood has great torsional strength, excelling most of the soft woods in
this respect, of coarse texture, close-grained and compact structure,
takes a fine polish. Annual rings clearly marked, very durable in
contact with the soil, shrinks and checks considerably in drying, the
very narrow sapwood greenish yellow, the heartwood brown, with shades
of red and green. Used for wagon hubs, trenails or pins, but
especially for railway ties, fence posts, and door sills. Also used
for boat parts, turnery, ornamentations, and locally for construction.
Abroad it is much used for furniture and farming implements and also
in turnery. At home in the Alleghany Mountains, extensively planted,
especially in the West.
=52. Honey Locust= (_Gleditschia triacanthos_) (Honey Shucks, Locust,
Black Locust, Brown Locust, Sweet Locust, False Acacia, Three-Thorned
Acacia). A medium-sized tree. Wood heavy, hard, strong, tough, durable
in contact with the soil, of coarse texture, susceptible to a good
polish. The narrow sapwood yellow, the heartwood brownish red. So far,
but little appreciated except for fences and fuel. Used to some extent
for wheel hubs, and locally in rough construction. Found from
Pennsylvania to Nebraska, and southward to Florida and Texas; locally
quite abundant.
=53. Locust= (_Robinia viscosa_) (Clammy Locust). Usually a shrub five
or six feet high, but known to reach a height of 40 feet in the
mountains of North Carolina, with the habit of a tree. Wood light
brown, heavy, hard, and close-grained. Not used to much extent in
manufacture. Range same as the preceding.
MAGNOLIA
=54. Magnolia= (_Magnolia glauca_) (Swamp Magnolia, Small Magnolia,
Sweet Bay, Beaver Wood). Small-sized tree. Heartwood reddish brown,
sap wood cream white. Sparingly used in manufacture. Ranges from Essex
County, Mass., to Long Island, N. Y., from New Jersey to Florida, and
west in the Gulf region to Texas.
=55. Magnolia= (_Magnolia tripetala_) (Umbrella Tree). A small-sized
tree. Wood in its quality similiar to the preceding. It may be easily
recognized by its great leaves, twelve to eighteen inches long, and
five to eight inches broad. This species as well as the preceding is
an ornamental tree. Ranges from Pennsylvania southward to the Gulf.
=56. Cucumber Tree= (_Magnolia accuminata_) (Tulip-wood, Poplar).
Medium- to large-sized tree. Heartwood yellowish brown, sapwood almost
white. Wood light, soft, satiny, close-grained, durable in contact
with the soil, resembling and sometimes confounded with tulip tree
(_Liriodendron tulipifera_) in the markets. The wood shrinks
considerably, but seasons without much injury, and works and stands
well. It bends readily when steamed, and takes stain and paint well.
Used in cooperage, for siding, for panelling and finishing lumber in
house, car and shipbuilding, etc., also in the manufacture of toys,
culinary woodenware, and backing for drawers. Most common in the
southern Alleghanies, but distributed from western New York to
southern Illinois, south through central Kentucky and Tennessee to
Alabama, and throughout Arkansas.
MAPLE
Wood heavy, hard, strong, stiff, and tough, of fine texture,
frequently wavy-grained, this giving rise to "curly" and "blister"
figures which are much admired. Not durable in the ground, or when
exposed. Maple is creamy white, with shades of light brown in the
heartwood, shrinks moderately, seasons, works, and stands well, wears
smoothly, and takes a fine polish. The wood is used in cooperage, and
for ceiling, flooring, panelling, stairway, and other finishing lumber
in house, ship, and car construction. It is used for the keels of
boats and ships, in the manufacture of implements and machinery, but
especially for furniture, where entire chamber sets of maple rival
those of oak. Maple is also used for shoe lasts and other form blocks;
for shoe pegs; for piano actions, school apparatus, for wood type in
show bill printing, tool handles, in wood carving, turnery, and scroll
work, in fact it is one of our most useful woods. The maples are
medium-sized trees, of fairly rapid growth, sometimes form forests,
and frequently constitute a large proportion of the arborescent
growth. They grow freely in parts of the Northern Hemisphere, and are
particularly luxuriant in Canada and the northern portions of the
United States.
=57. Sugar Maple= (_Acer saccharum_) (Hard Maple, Rock Maple). Medium-
to large-sized tree, very common, forms considerable forests, and is
especially esteemed. The wood is close-grained, heavy, fairly hard and
strong, of compact structure. Heartwood brownish, sapwood lighter
color; it can be worked to a satin-like surface and take a fine
polish, it is not durable if exposed, and requires a good deal of
seasoning. Medullary rays small but distinct. The "curly" or "wavy"
varieties furnish wood of much beauty, the peculiar contortions of the
grain called "bird's eye" being much sought after, and used as veneer
for panelling, etc. It is used in all good grades of furniture,
cabinetmaking, panelling, interior finish, and turnery; it is not
liable to warp and twist. It is also largely used for flooring, for
rollers for wringers and mangling machines, for which there is a large
and increasing demand. The peculiarity known as "bird's eye," and
which causes a difficulty in working the wood smooth, owing to the
little pieces like knots lifting up, is supposed to be due to the
action of boring insects. Its resistance to compression across the
grain is higher than that of most other woods. Ranges from Maine to
Minnesota, abundant, with birch, in the region of the Great Lakes.
=58. Red Maple= (_Acer rubrum_) (Swamp Maple, Soft Maple, Water Maple).
Medium-sized tree. Like the preceding but not so valuable. Scattered
along water-courses and other moist localities. Abundant. Maine to
Minnesota, southward to northern Florida.
=59. Silver Maple= (_Acer saccharinum_) (Soft Maple, White Maple,
Silver-Leaved Maple). Medium- to large-sized tree, common. Wood
lighter, softer, and inferior to _Acer saccharum_, and usually offered
in small quantities and held separate in the markets. Heartwood
reddish brown, sapwood ivory white, fine-grained, compact structure.
Fibres sometimes twisted, weaved, or curly. Not durable. Used in
cooperage for woodenware, turnery articles, interior decorations and
flooring. Valley of the Ohio, but occurs from Maine to Dakota and
southward to Florida.
=60. Broad-Leaved Maple= (_Acer macrophyllum_) (Oregon Maple).
Medium-sized tree, forms considerable forests, and, like the preceding
has a lighter, softer, and less valuable wood than _Acer saccharum_.
Pacific Coast regions.
=61. Mountain Maple= (_Acer spicatum_). Small-sized tree. Heartwood pale
reddish brown, sapwood lighter color. Wood light, soft, close-grained,
and susceptible of high polish. Ranges from lower St. Lawrence River
to northern Minnesota and regions of the Saskatchewan River; south
through the Northern States and along the Appalachian Mountains to
Georgia.
=62. Ash-Leaved Maple= (_Acer negundo_) (Box Elder). Medium- to
large-sized tree. Heartwood creamy white, sapwood nearly white. Wood
light, soft, close-grained, not strong. Used for woodenware and paper
pulp. Distributed across the continent, abundant throughout the
Mississippi Valley along banks of streams and borders of swamps.
=63. Striped Maple= (_Acer Pennsylvanicum_) (Moose-wood). Small-sized
tree. Produces a very white wood much sought after for inlaid and for
cabinet work. Wood is light, soft, close-grained, and takes a fine
polish. Not common. Occurs from Pennsylvania to Minnesota.
MULBERRY
=64. Red Mulberry= (_Morus rubra_). A small-sized tree. Wood moderately
heavy, fairly hard and strong, rather tough, of coarse texture, very
durable in contact with the soil. The sapwood whitish, heartwood
yellow to orange brown, shrinks and checks considerably in drying,
works well and stands well. Used in cooperage and locally in
construction, and in the manufacture of farm implements. Common in the
Ohio and Mississippi Valleys, but widely distributed in the eastern
United States.
MYRTLE (See Laurel)
OAK
Wood very variable, usually very heavy and hard, very strong and
tough, porous, and of coarse texture. The sapwood whitish, the
heartwood "oak" to reddish brown. It shrinks and checks badly, giving
trouble in seasoning, but stands well, is durable, and little subject
to the attacks of boring insects. Oak is used for many purposes, and
is the chief wood used for tight cooperage; it is used in
shipbuilding, for heavy construction, in carpentry, in furniture, car
and wagon work, turnery, and even in woodcarving. It is also used in
all kinds of farm implements, mill machinery, for piles and wharves,
railway ties, etc., etc. The oaks are medium- to large-sized trees,
forming the predominant part of a large proportion of our
broad-leaved forests, so that these are generally termed "oak
forests," though they always contain considerable proportion of other
kinds of trees. Three well-marked kinds--white, red, and live oak--are
distinguished and kept separate in the markets. Of the two principal
kinds "white oak" is the stronger, tougher, less porous, and more
durable. "Red oak" is usually of coarser texture, more porous, often
brittle, less durable, and even more troublesome in seasoning than
white oak. In carpentry and furniture work red oak brings the same
price at present as white oak. The red oaks everywhere accompany the
white oaks, and, like the latter, are usually represented by several
species in any given locality. "Live oak," once largely employed in
shipbuilding, possesses all the good qualities, except that of size,
of white oak, even to a greater degree. It is one of the heaviest,
hardest, toughest, and most durable woods of this country. In
structure it resembles the red oak, but is less porous.
=65. White Oak= (_Quercus alba_) (American Oak). Medium-to large-sized
tree. Heartwood light brown, sapwood lighter color. Annual rings well
marked, medullary rays broad and prominent. Wood tough, strong, heavy,
hard, liable to check in seasoning, durable in contact with the soil,
takes a high polish, very elastic, does not shrink much, and can be
bent to any form when steamed. Used for agricultural implements, tool
handles, furniture, fixtures, interior finish, car and wagon
construction, beams, cabinet work, tight cooperage, railway ties,
etc., etc. Because of the broad medullary rays, it is generally
"quarter-sawn" for cabinet work and furniture. Common in the Eastern
States, Ohio and Mississippi Valleys. Occurs throughout the eastern
United States.
=66. White Oak= (_Quercus durandii_). Medium- to small-sized tree. Wood
in its quality and uses similiar to the preceding. Texas, eastward to
Alabama.
=67. White Oak= (_Quercus garryana_) (Western White Oak). Medium- to
large-sized tree. Stronger, more durable, and wood more compact than
_Quercus alba_. Washington to California.
=68. White Oak= (_Quercus lobata_). Medium- to large-sized tree. Largest
oak on the Pacific Coast. Wood in its quality and uses similar to
_Quercus alba_, only it is finer-grained. California.
=69. Bur Oak= (_Quercus macrocarpa_) (Mossy-Cup Oak, Over-Cup Oak).
Large-sized tree. Heartwood "oak" brown, sapwood lighter color. Wood
heavy, strong, close-grained, durable in contact with the soil. Used
in ship- and boatbuilding, all sorts of construction, interior finish
of houses, cabinet work, tight cooperage, carriage and wagon work,
agricultural implements, railway ties, etc., etc. One of the most
valuable and most widely distributed of American oaks, 60 to 80 feet
in height, and, unlike most of the other oaks, adapts itself to
varying climatic conditions. It is one of the most durable woods when
in contact with the soil. Common, locally abundant. Ranges from
Manitoba to Texas, and from the foot hills of the Rocky Mountains to
the Atlantic Coast. It is the most abundant oak of Kansas and
Nebraska, and forms the scattered forests known as "The oak openings"
of Minnesota.
=70. Willow Oak= (_Quercus phellos_) (Peach oak). Small to medium-sized
tree. Heartwood pale reddish brown, sapwood lighter color. Wood heavy,
hard, strong, coarse-grained. Occasionally used in construction. New
York to Texas, and northward to Kentucky.
=71. Swamp White Oak= (_Quercus bicolor_ var. _platanoides_).
Large-sized tree. Heartwood pale brown, sapwood the same color. Wood
heavy, hard, strong, tough, coarse-grained, checks considerably in
seasoning. Used in construction, interior finish of houses,
carriage-and boatbuilding, agricultural implements, in cooperage,
railway ties, fencing, etc., etc. Ranges from Quebec to Georgia and
westward to Arkansas. Never abundant. Most abundant in the Lake
States.
=72. Over-Cup Oak= (_Quercus lyrata_) (Swamp White Oak, Swamp Post Oak).
Medium to large-sized tree, rather restricted, as it grows in the
swampy districts of Carolina and Georgia. Is a larger tree than most
of the other oaks, and produces an excellent timber, but grows in
districts difficult of access, and is not much used. Lower Mississippi
and eastward to Delaware.
=73. Pin Oak= (_Quercus palustris_) (Swamp Spanish Oak, Water Oak).
Medium- to large-sized tree. Heartwood pale brown with dark-colored
sap wood. Wood heavy, strong, and coarse-grained. Common along the
borders of streams and swamps, attains its greatest size in the valley
of the Ohio. Arkansas to Wisconsin, and eastward to the Alleghanies.
=74. Water Oak= (_Quercus aquatica_) (Duck Oak, Possum Oak). Medium- to
large-sized tree, of extremely rapid growth. Eastern Gulf States,
eastward to Delaware and northward to Missouri and Kentucky.
=75. Chestnut Oak= (_Quercus prinus_) (Yellow Oak, Rock Oak, Rock
Chestnut Oak). Heartwood dark brown, sapwood lighter color. Wood
heavy, hard, strong, tough, close-grained, durable in contact with the
soil. Used for railway ties, fencing, fuel, and locally for
construction. Ranges from Maine to Georgia and Alabama, westward
through Ohio, and southward to Kentucky and Tennessee.
=76. Yellow Oak= (_Quercus acuminata_) (Chestnut Oak, Chinquapin Oak).
Medium- to large-sized tree. Heartwood dark brown, sapwood pale brown.
Wood heavy, hard, strong, close-grained, durable in contact with the
soil. Used in the manufacture of wheel stock, in cooperage, for
railway ties, fencing, etc., etc. Ranges from New York to Nebraska and
eastern Kansas, southward in the Atlantic region to the District of
Columbia, and west of the Alleghanies southward to the Gulf States.
=77. Chinquapin Oak= (_Quercus prinoides_) (Dwarf Chinquapin Oak, Scrub
Chestnut Oak). Small-sized tree. Heartwood light brown, sapwood darker
color. Does not enter the markets to any great extent. Ranges from
Massachusetts to North Carolina, westward to Missouri, Nebraska,
Kansas, and eastern Texas. Reaches its best form in Missouri and
Kansas.
=78. Basket Oak= (_Quercus michauxii_) (Cow Oak). Large-sized tree.
Locally abundant. Lower Mississippi and eastward to Delaware.
=79. Scrub Oak= (_Quercus ilicifolia_ var. _pumila_) (Bear Oak).
Small-sized tree. Heartwood light brown, sapwood darker color. Wood
heavy, hard, strong, and coarse-grained. Found in New England and
along the Alleghanies.
=80. Post Oak= (_Quercus obtusiloda_ var. _minor_) (Iron Oak). Medium-
to large-sized tree, gives timber of great strength. The color is of a
brownish yellow hue, close-grained, and often superior to the white
oak (_Quercus alba_) in strength and durability. It is used for posts
and fencing, and locally for construction. Arkansas to Texas, eastward
to New England and northward to Michigan.
=81. Red Oak= (_Quercus rubra_) (Black Oak). Medium- to large-sized
tree. Heartwood light brown to red, sapwood lighter color. Wood
coarse-grained, well-marked annual rings, medullary rays few but
broad. Wood heavy, hard, strong, liable to check in seasoning. It is
found over the same range as white oak, and is more plentiful. Wood is
spongy in grain, moderately durable, but unfit for work requiring
strength. Used for agricultural implements, furniture, bob sleds,
vehicle parts, boxes, cooperage, woodenware, fixtures, interior
finish, railway ties, etc., etc. Common in all parts of its range.
Maine to Minnesota, and southward to the Gulf.
=82. Black Oak= (_Quercus tinctoria_ var. _velutina_) (Yellow Oak).
Medium- to large-sized tree. Heartwood bright brown tinged with red,
sapwood lighter color. Wood heavy, hard, strong, coarse-grained,
checks considerably in seasoning. Very common in the Southern States,
but occurring North as far as Minnesota, and eastward to Maine.
=83. Barren Oak= (_Quercus nigra_ var. _marilandica_) (Black Jack, Jack
Oak). Small-sized tree. Heartwood dark brown, sapwood lighter color.
Wood heavy, hard, strong, coarse-grained, not valuable. Used in the
manufacture of charcoal and for fuel. New York to Kansas and Nebraska,
and southward to Florida. Rare in the North, but abundant in the
South.
=84. Shingle Oak= (_Quercus imbricaria_) (Laurel Oak). Small to
medium-sized tree. Heartwood pale reddish brown, sapwood lighter
color. Wood heavy, hard, strong, coarse-grained, checks considerably
in drying. Used for shingles and locally for construction. Rare in the
east, most abundant in the lower Ohio Valley. From New York to
Illinois and southward. Reaches its greatest size in southern Illinois
and Indiana.
=85. Spanish Oak= (_Quercus digitata_ var. _falcata_) (Red Oak).
Medium-sized tree. Heartwood light reddish brown, sapwood much
lighter. Wood heavy, hard, strong, coarse-grained, and checks
considerably in seasoning. Used locally for construction, and has high
fuel value. Common in south Atlantic and Gulf region, but found from
Texas to New York, and northward to Missouri and Kentucky.
=86. Scarlet Oak= (_Quercus coccinea_). Medium- to large-sized tree.
Heartwood light reddish-brown, sapwood darker color. Wood heavy, hard,
strong, and coarse-grained. Best developed in the lower basin of the
Ohio, but found from Minnesota to Florida.
=87. Live Oak= (_Quercus virens_) (Maul Oak). Medium- to large-sized
tree. Grows from Maryland to the Gulf of Mexico, and often attains a
height of 60 feet and 4 feet in diameter. The wood is hard, strong,
and durable, but of rather rapid growth, therefore not as good quality
as _Quercus alba_. The live oak of Florida is now reserved by the
United States Government for Naval purposes. Used for mauls and
mallets, tool handles, etc., and locally for construction. Scattered
along the coast from Maryland to Texas.
=88. Live Oak= (_Quercus chrysolepis_) (Maul Oak, Valparaiso Oak).
Medium- to small-sized tree. California.
OSAGE ORANGE
=89. Osage Orange= (_Maclura aurantiaca_) (Bois d'Arc). A small-sized
tree of fairly rapid growth. Wood very heavy, exceedingly hard,
strong, not tough, of moderately coarse texture, and very durable and
elastic. Sapwood yellow, heartwood brown on the end face, yellow on
the longitudinal faces, soon turning grayish brown if exposed. It
shrinks considerably in drying, but once dry it stands unusually well.
Much used for wheel stock, and wagon framing; it is easily split, so
is unfit for wheel hubs, but is very suitable for wheel spokes. It is
considered one of the timbers likely to supply the place of black
locust for insulator pins on telegraph poles. Seems too little
appreciated; it is well suited for turned ware and especially for
woodcarving. Used for spokes, insulator pins, posts, railway ties,
wagon framing, turnery, and woodcarving. Scattered through the rich
bottoms of Arkansas and Texas.
PAPAW
=90. Papaw= (_Asimina triloba_) (Custard Apple). Small-sized tree, often
only a shrub, Heartwood pale, yellowish green, sapwood lighter color.
Wood light, soft, coarse-grained, and spongy. Not used to any extent
in manufacture. Occurs in eastern and central Pennsylvania, west as
far as Michigan and Kansas, and south to Florida and Texas. Often
forming dense thickets in the lowlands bordering the Mississippi
River.
PERSIMMON
=91. Persimmon= (_Diospyros Virginiana_). Small to medium-sized tree.
Wood very heavy, and hard, strong and tough; resembles hickory, but is
of finer texture and elastic, but liable to split in working. The
broad sapwood cream color, the heartwood brown, sometimes almost
black. The persimmon is the Virginia date plum, a tree of 30 to 50
feet high, and 18 to 20 inches in diameter; it is noted chiefly for
its fruit, but it produces a wood of considerable value. Used in
turnery, for wood engraving, shuttles, bobbins, plane stock, shoe lasts,
and largely as a substitute for box (_Buxus sempervirens_)--especially
the black or Mexican variety,--also used for pocket rules and drawing
scales, for flutes and other wind instruments. Common, and best
developed in the lower Ohio Valley, but occurs from New York to Texas
and Missouri.
POPLAR (See also Tulip Wood)
Wood light, very soft, not strong, of fine texture, and whitish,
grayish to yellowish color, usually with a satiny luster. The wood
shrinks moderately (some cross-grained forms warp excessively), but
checks very little in seasoning; is easily worked, but is not durable.
Used in cooperage, for building and furniture lumber, for crates and
boxes (especially cracker boxes), for woodenware, and paper pulp.
=92. Cottonwood= (_Populus monilifera_, var. _angulata_) (Carolina
Poplar). Large-sized tree, forms considerable forests along many of
the Western streams, and furnishes most of the cottonwood of the
market. Heartwood dark brown, sapwood nearly white. Wood light, soft,
not strong, and close-grained (see Fig. 14). Mississippi Valley and
West. New England to the Rocky Mountains.
=93. Cottonwood= (_Populus fremontii_ var. _wislizeni_). Medium-to
large-sized tree. Common. Wood in its quality and uses similiar to the
preceding, but not so valuable. Texas to California.
[Illustration: Fig. 14. A Large Cottonwood. One of the
Associates of Red Gum.]
=94. Black Cottonwood= (_Populus trichocarpa_ var. _heterophylla_)
(Swamp Cottonwood, Downy Poplar). The largest deciduous tree of
Washington. Very common. Heartwood dull brown, sapwood lighter brown.
Wood soft, close-grained. Is now manufactured into lumber in the West
and South, and used in interior finish of buildings. Northern Rocky
Mountains and Pacific region.
=95. Poplar= (_Populus grandidentata_) (Large-Toothed Aspen).
Medium-sized tree. Heartwood light brown, sapwood nearly white. Wood
soft and close-grained, neither strong nor durable. Chiefly used for
wood pulp. Maine to Minnesota and southward along the Alleghanies.
=96. White Poplar= (_Populus alba_) (Abele-Tree). Small to medium-sized
tree. Wood in its quality and uses similar to the preceding. Found
principally along banks of streams, never forming forests. Widely
distributed in the United States.
=97. Lombardy Poplar= (_Populus nigra italica_). Medium-to large-sized
tree. This species is the first ornamental tree introduced into the
United States, and originated in Afghanistan. Does not enter into the
markets. Widely planted in the United States.
=98. Balsam= (_Populus balsamifera_) (Balm of Gilead, Tacmahac). Medium-
to large-sized tree. Heartwood light brown, sapwood nearly white. Wood
light, soft, not strong, close-grained. Used extensively in the
manufacture of paper pulp. Common all along the northern boundary of
the United States.
=99. Aspen= (_Populus tremuloides_) (Quaking Aspen). Small to
medium-sized tree, often forming extensive forests, and covering
burned areas. Heartwood light brown, sapwood nearly white. Wood light,
soft, close-grained, neither strong nor durable. Chiefly used for
woodenware, cooperage, and paper pulp. Maine to Washington and
northward, and south in the western mountains to California and New
Mexico.
RED GUM (See Gum)
SASSAFRAS
=100. Sassafras= (_Sassafras sassafras_). Medium-sized tree, largest in
the lower Mississippi Valley. Wood light, soft, not strong, brittle,
of coarse texture, durable in contact with the soil. The sapwood
yellow, the heartwood orange brown. Used to some extent in slack
cooperage, for skiff- and boatbuilding, fencing, posts, sills, etc.
Occurs from New England to Texas and from Michigan to Florida.
SOUR GUM (See Gum)
SOURWOOD
=101. Sourwood= (_Oxydendrum arboreum_) (Sorrel-Tree). A slender tree,
reaching the maximum height of 60 feet. Heartwood reddish brown,
sapwood lighter color. Wood heavy, hard, strong, close-grained, and
takes a fine polish. Ranges from Pennsylvania, along the Alleghanies,
to Florida and Alabama, westward through Ohio to southern Indiana and
southward through Arkansas and Louisiana to the Coast.
SWEET GUM (See Gum)
SYCAMORE
=102. Sycamore= (_Platanus occidentalis_) (Buttonwood, Button-Ball Tree,
Plane Tree, Water Beech). A large-sized tree, of rapid growth. One of
the largest deciduous trees of the United States, sometimes attaining
a height of 100 feet. It produces a timber that is moderately heavy,
quite hard, stiff, strong, and tough, usually cross-grained; of coarse
texture, difficult to split and work, shrinks moderately, but warps
and checks considerably in seasoning, but stands well, and is not
considered durable for outside work, or in contact with the soil. It
has broad medullary rays, and much of the timber has a beautiful
figure. It is used in slack cooperage, and quite extensively for
drawers, backs, and bottoms, etc., in furniture work. It is also used
for cabinet work, for tobacco boxes, crates, desks, flooring,
furniture, ox-yokes, butcher blocks, and also for finishing lumber,
where it has too long been underrated. Common and largest in the Ohio
and Mississippi Valleys, at home in nearly all parts of the eastern
United States.
=103. Sycamore= (_Platanus racemosa_). The California species,
resembling in its wood the Eastern form. Not used to any great extent.
TULIP TREE
=104. Tulip Tree= (_Liriodendron tulipifera_) (Yellow Poplar, Tulip
Wood, White Wood, Canary Wood, Poplar, Blue Poplar, White Poplar,
Hickory Poplar). A medium- to large-sized tree, does not form forests,
but is quite common, especially in the Ohio basin. Wood usually light,
but varies in weight, it is soft, tough, but not strong, of fine
texture, and yellowish color. The wood shrinks considerably, but
seasons without much injury, and works and stands extremely well.
Heartwood light yellow or greenish brown, the sapwood is thin, nearly
white, and decays rapidly. The heartwood is fairly durable when
exposed to the weather or in contact with the soil. It bends readily
when steamed, and takes stain and paint well. The mature forest-grown
tree has a long, straight, cylindrical bole, clear of branches for at
least two thirds of its length, surmounted by a short, open, irregular
crown. When growing in the open, the tree maintains a straight stem,
but the crown extends almost to the ground, and is of conical shape.
Yellow poplar, or tulip wood, ordinarily grows to a height of from 100
to 125 feet, with a diameter of from 3 to 6 feet, and a clear length
of about 70 feet. Trees have been found 190 feet high and ten feet in
diameter. Used in cooperage, for siding, for panelling and finishing
lumber in houses, car- and shipbuilding, for sideboards, panels of
wagons and carriages, for aeroplanes, for automobiles, also in the
manufacture of furniture farm implements, machinery, for pump logs,
and almost every kind of common woodenware, boxes shelving, drawers,
etc., etc. Also in the manufacture of toys, culinary woodenware, and
backing for veneer. It is in great demand throughout the vehicle and
implement trade, and also makes a fair grade of wood pulp. In fact the
tulip tree is one of the most useful of woods throughout the
woodworking industry of this country. Occurs from New England to
Missouri and southward to Florida.
TUPELO (See Gum)
WAAHOO
=105. Waahoo= (_Evonymus atropurpureus_). (Burning Bush, Spindle Tree).
A small-sized tree. Wood white, tinged with orange; heavy, hard,
tough, and close-grained, works well and stands well. Used principally
for arrows and spindles. Widely distributed. Usually a shrub six to
ten feet high, becoming a tree only in southern Arkansas and Oklahoma.
WALNUT
=106. Black Walnut= (_Juglans nigra_) (Walnut). A large, beautiful, and
quickly-growing tree, about 60 feet and upwards in height. Wood heavy,
hard, strong, of coarse texture, very durable in contact with the
soil. The narrow sapwood whitish, the heartwood dark, rich, chocolate
brown, sometimes almost black; aged trees of fine quality bring fancy
prices. The wood shrinks moderately in seasoning, works well and
stands well, and takes a fine polish. It is quite handsome, and has
been for a long time the favorite wood for cabinet and furniture
making. It is used for gun-stocks, fixtures, interior decoration,
veneer, panelling, stair newells, and all classes of work demanding a
high priced grade of wood. Black walnut is a large tree with stout
trunk, of rapid growth, and was formerly quite abundant throughout
the Alleghany region. Occurs from New England to Texas, and from
Michigan to Florida. Not common.
WHITE WALNUT (See Butternut)
WHITE WOOD (See Tulip and also Basswood)
WHITE WILLOW
=107. White Willow= (_Salix alba_ var. _vitellina_) (Willow, Yellow
Willow, Blue Willow). The wood is very soft, light, flexible, and
fairly strong, is fairly durable in contact with the soil, works well
and stands well when seasoned. Medium-sized tree, characterized by a
short, thick trunk, and a large, rather irregular crown composed of
many branches. The size of the tree at maturity varies with the
locality. In the region where it occurs naturally, a height of 70 to
80 feet, and a diameter of three to four feet are often attained. When
planted in the Middle West, a height of from 50 to 60 feet, and a
diameter of one and one-half to two feet are all that may be expected.
When closely planted on moist soil, the tree forms a tall, slender
stem, well cleared branches. Is widely naturalized in the United
States. It is used in cooperage, for woodenware, for cricket and
baseball bats, for basket work, etc. Charcoal made from the wood is
used in the manufacture of gunpowder. It has been generally used for
fence posts on the Northwestern plains, because of scarcity of better
material. Well seasoned posts will last from four to seven years.
Widely distributed throughout the United States.
=108. Black Willow= (_Salix nigra_). Small-sized tree. Heartwood light
reddish brown, sapwood nearly white. Wood soft, light, not strong,
close-grained, and very flexible. Used in basket making, etc. Ranges
from New York to Rocky Mountains and southward to Mexico.
=109. Shining Willow= (_Salix lucida_). A small-sized tree. Wood in its
quality and uses similiar to the preceding. Ranges from Newfoundland
to Rocky Mountains and southward to Pennsylvania and Nebraska.
=110. Perch Willow= (_Salix amygdaloides_) (Almond-leaf Willow). Small
to medium-sized tree. Heartwood light brown, sapwood lighter color.
Wood light, soft, flexible, not strong, close-grained. Uses similiar
to the preceding. Follows the water courses and ranges across the
continent; less abundant in New England than elsewhere. Common in the
West.
=111. Long-Leaf Willow= (_Salix fluviatilis_) (Sand Bar Willow). A
small-sized tree. Ranges from the Arctic Circle to Northern Mexico.
=112. Bebb Willow= (_Salix bebbiana_ var. _rostrata_). A small-sized
tree. More abundant in British America than in the United States,
where it ranges southward to Pennsylvania and westward to Minnesota.
=113. Glaucous Willow= (_Salix discolor_) (Pussy Willow). A small-sized
tree. Common along the banks of streams, and ranges from Nova Scotia
to Manitoba, and south to Delaware; west to Indiana and northwestern
Missouri.
=114. Crack Willow= (_Salix fragilis_). A medium to large-sized tree.
Wood is very soft, light, very flexible and fairly strong, is fairly
durable in contact with the soil, works well and stands well. Used
principally for basket making, hoops, etc., and to produce charcoal
for gunpowder. Very common, and widely distributed in the United
States.
=115. Weeping Willow= (_Salix babylonica_). Medium- to large-sized tree.
Wood similiar to _Salix nigra_, but not so valuable. Mostly an
ornamental tree. Originally came from China. Widely planted in the
United States.
YELLOW WOOD
=116. Yellow Wood= (_Cladrastis lutea_) (Virgilia). A small to
medium-sized tree. Wood yellow to pale brown, heavy, hard,
close-grained and strong. Not used to much extent in manufacturing.
Not common. Found principally on the limestone cliffs of Kentucky,
Tennessee, and North Carolina.
SECTION IV
GRAIN, COLOR, ODOR, WEIGHT, AND FIGURE IN WOOD
DIFFERENT GRAINS OF WOOD
The terms "fine-grained," "coarse-grained," "straight-grained," and
"cross-grained" are frequently applied in the trade. In common usage,
wood is coarse-grained if its annual rings are wide; fine-grained if
they are narrow. In the finer wood industries a fine-grained wood is
capable of high polish, while a coarse-grained wood is not, so that in
this latter case the distinction depends chiefly on hardness, and in
the former on an accidental case of slow or rapid growth. Generally if
the direction of the wood fibres is parallel to the axis of the stem
or limb in which they occur, the wood is straight-grained; but in many
cases the course of the fibres is spiral or twisted around the tree
(as shown in Fig. 15), and sometimes commonly in the butts of gum and
cypress, the fibres of several layers are oblique in one direction,
and those of the next series of layers are oblique in the opposite
direction. (As shown in Fig. 16 the wood is cross or twisted grain.)
Wavy-grain in a tangential plane as seen on the radial section is
illustrated in Fig. 17, which represents an extreme case observed in
beech. This same form also occurs on the radial plane, causing the
tangential section to appear wavy or in transverse folds.
When wavy grain is fine (_i.e._, the folds or ridges small but
numerous) it gives rise to the "curly" structure frequently seen in
maple. Ordinarily, neither wavy, spiral, nor alternate grain is
visible on the cross-section; its existence often escapes the eye even
on smooth, longitudinal faces in the sawed material, so that the only
guide to their discovery lies in splitting the wood in two, in the two
normal plains.
[Illustration: Fig. 15. Spiral Grain. Season checks, after
removal of bark, indicate the direction of the fibres or
grain of the wood.]
[Illustration: Fig. 16. Alternating Spiral Grain in Cypress.
Side and end view of same piece. When the bark was at _o_,
the grain of this piece was straight. From that time, each
year it grew more oblique in one direction, reaching a climax
at _a_, and then turned back in the opposite direction. These
alternations were repeated periodically, the bark sharing in
these changes.]
Generally the surface of the wood under the bark, and therefore also
that of any layer in the interior, is not uniform and smooth, but is
channelled and pitted by numerous depressions, which differ greatly in
size and form. Usually, any one depression or elevation is restricted
to one or few annual layers (_i.e._, seen only in one or few rings)
and is then lost, being compensated (the surface at the particular
spot evened up) by growth. In some woods, however, any depression or
elevation once attained grows from year to year and reaches a maximum
size, which is maintained for many years, sometimes throughout life.
In maple, where this tendency to preserve any particular contour is
very great, the depressions and elevations are usually small
(commonly less than one-eighth inch) but very numerous.
On tangent boards of such wood, the sections, pits, and prominences
appear as circlets, and give rise to the beautiful "bird's eye" or
"landscape" structure. Similiar structures in the burls of black ash,
maple, etc., are frequently due to the presence of dormant buds, which
cause the surface of all the layers through which they pass to be
covered by small conical elevations, whose cross-sections on the sawed
board appear as irregular circlets or islets, each with a dark speck,
the section of the pith or "trace" of the dormant bud in the center.
[Illustration: Fig. 17. Wavy Grain in Beech (_after
Nordlinger_).]
In the wood of many broad-leaved trees the wood fibres are much longer
when full grown than when they are first formed in the cambium or
growing zone. This causes the tips of each fibre to crowd in between
the fibres above and below, and leads to an irregular interlacement of
these fibres, which adds to the toughness, but reduces the
cleavability of the wood. At the juncture of the limb and stem the
fibres on the upper and lower sides of the limb behave differently.
On the lower side they run from the stem into the limb, forming an
uninterrupted strand or tissue and a perfect union. On the upper side
the fibres bend aside, are not continuous into the limb, and hence the
connection is not perfect (see Fig. 18). Owing to this arrangement of
the fibres, the cleft made in splitting never runs into the knot if
started on the side above the limb, but is apt to enter the knot if
started below, a fact well understood in woodcraft. When limbs die,
decay, and break off, the remaining stubs are surrounded, and may
finally be covered by the growth of the trunk and thus give rise to
the annoying "dead" or "loose" knots.
[Illustration: Fig. 18. Section of Wood showing Position of
the Grain at Base of a Limb. P, pith of both stem and limb;
1-7, seven yearly layers of wood; _a_, _b_, knot or basal
part of a limb which lived for four years, then died and
broke off near the stem, leaving the part to the left of _a_,
_b_, a "sound" knot, the part to the right a "dead" knot,
which would soon be entirely covered by the growing stem.]
COLOR AND ODOR OF WOOD
Color, like structure, lends beauty to the wood, aids in its
identification, and is of great value in the determination of its
quality. If we consider only the heartwood, the black color of the
persimmon, the dark brown of the walnut, the light brown of the white
oaks, the reddish brown of the red oaks, the yellowish white of the
tulip and poplars, the brownish red of the redwood and cedars, the
yellow of the papaw and sumac, are all reliable marks of distinction
and color. Together with luster and weight, they are only too often
the only features depended upon in practice. Newly formed wood, like
that of the outer few rings, has but little color. The sapwood
generally is light, and the wood of trees which form no heartwood
changes but little, except when stained by forerunners of disease.
The different tints of colors, whether the brown of oak, the orange
brown of pine, the blackish tint of walnut, or the reddish cast of
cedar, are due to pigments, while the deeper shade of the summer-wood
bands in pine, cedar, oak, or walnut is due to the fact that the wood
being denser, more of the colored wood substance occurs on a given
space, _i.e._, there is more colored matter per square inch. Wood is
translucent, a thin disk of pine permitting light to pass through
quite freely. This translucency affects the luster and brightness of
lumber.
When lumber is attacked by fungi, it becomes more opaque, loses its
brightness, and in practice is designated "dead," in distinction to
"live" or bright timber. Exposure to air darkens all wood; direct
sunlight and occasional moistening hasten this change, and cause it to
penetrate deeper. Prolonged immersion has the same effect, pine wood
becoming a dark gray, while oak changes to a blackish brown.
Odor, like color, depends on chemical compounds, forming no part of
the wood substance itself. Exposure to weather reduces and often
changes the odor, but a piece of long-leaf pine, cedar, or camphor
wood exhales apparently as much odor as ever when a new surface is
exposed. Heartwood is more odoriferous than sapwood. Many kinds of
wood are distinguished by strong and peculiar odors. This is
especially the case with camphor, cedar, pine, oak, and mahogany, and
the list would comprise every kind of wood in use were our sense of
smell developed in keeping with its importance.
Decomposition is usually accompanied by pronounced odors. Decaying
poplar emits a disagreeable odor, while red oak often becomes
fragrant, its smell resembling that of heliotrope.
WEIGHT OF WOOD
A small cross-section of wood (as in Fig. 19) dropped into water
sinks, showing that the substance of which wood fibre or wood is built
up is heavier than water. By immersing the wood successively in
heavier liquids, until we find a liquid in which it does not sink, and
comparing the weight of the same with water, we find that wood
substance is about 1.6 times as heavy as water, and that this is as
true of poplar as of oak or pine.
[Illustration: Fig. 19. Cross-section of a Group of Wood
Fibres (Highly Magnified.)]
Separating a single cell (as shown in Fig. 20, _a_), drying and then
dropping it into water, it floats. The air-filled cell cavity or
interior reduces its weight, and, like an empty corked bottle, it
weighs less than the water. Soon, however, water soaks into the cell,
when it fills up and sinks. Many such cells grown together, as in a
block of wood, when all or most of them are filled with water, will
float as long as the majority of them are empty or only partially
filled. This is why a green, sappy pine pole soon sinks in "driving"
(floating down stream). Its cells are largely filled before it is
thrown in, and but little additional water suffices to make its weight
greater than that of the water. In a good-sized white pine log,
composed chiefly of empty cells (heartwood), the water requires a very
long time to fill up the cells (five years would not suffice to fill
them all), and therefore the log may float for many months. When the
wall of the wood fibre is very thick (five eighths or more of the
volume, as in Fig. 20, _b_), the fibre sinks whether empty or filled.
This applies to most of the fibres of the dark summer-wood bands in
pines, and to the compact fibres of oak or hickory, and many,
especially tropical woods, have such thick-walled cells and so little
empty or air space that they never float.
[Illustration: Fig. 20. Isolated Fibres of Wood.]
Here, then, are the two main factors of weight in wood; the amount of
cell wall or wood substance constant for any given piece, and the
amount of water contained in the wood, variable even in the standing
tree, and only in part eliminated in drying.
The weight of the green wood of any species varies chiefly as a second
factor, and is entirely misleading, if the relative weight of
different kinds is sought. Thus some green sticks of the otherwise
lighter cypress and gum sink more readily than fresh oak.
The weight of sapwood or the sappy, peripheral part of our common
lumber woods is always great, whether cut in winter or summer. It
rarely falls much below forty-five pounds, and commonly exceeds
fifty-five pounds to the cubic foot, even in our lighter wooded
species. It follows that the green wood of a sapling is heavier than
that of an old tree, the fresh wood from a disk of the upper part of a
tree is often heavier than that of the lower part, and the wood near
the bark heavier than that nearer the pith; and also that the
advantage of drying the wood before shipping is most important in
sappy and light kinds.
When kiln-dried, the misleading moisture factor of weight is uniformly
reduced, and a fair comparison possible. For the sake of convenience
in comparison, the weight of wood is expressed either as the weight
per cubic foot, or, what is still more convenient, as specific weight
or density. If an old long-leaf pine is cut up (as shown in Fig. 21)
the wood of disk No. 1 is heavier than that of disk No. 2, the latter
heavier than that of disk No. 3, and the wood of the top disk is found
to be only about three fourths as heavy as that of disk No. 1.
Similiarly, if disk No. 2 is cut up, as in the figure, the specific
weight of the different parts is:
_a_, about 0.52
_b_, about 0.64
_c_, about 0.67
_d_, _e_, _f_, about 0.65
showing that in this disk at least the wood formed during the many
years' growth, represented in piece _a_, is much lighter than that of
former years. It also shows that the best wood is the middle part,
with its large proportion of dark summer bands.
[Illustration: Fig. 21. Orientation of Wood Samples.]
Cutting up all disks in the same way, it will be found that the piece
_a_ of the first disk is heavier than the piece _a_ of the fifth, and
that piece _c_ of the first disk excels the piece _c_ of all the other
disks. This shows that the wood grown during the same number of years
is lighter in the upper parts of the stem; and if the disks are
smoothed on the radial surfaces and set up one on top of the other in
their regular order, for the sake of comparison, this decrease in
weight will be seen to be accompanied by a decrease in the amount of
summer-wood. The color effect of the upper disks is conspicuously
lighter. If our old pine had been cut one hundred and fifty years ago,
before the outer, lighter wood was laid on, it is evident that the
weight of the wood of any one disk would have been found to increase
from the center outward, and no subsequent decrease could have been
observed.
In a thrifty young pine, then, the wood is heavier from the center
outward, and lighter from below upward; only the wood laid on in old
age falls in weight below the average. The number of brownish bands of
summer-wood are a direct indication of these differences. If an old
oak is cut up in the same manner, the butt cut is also found heaviest
and the top lightest, but, unlike the disk of pine, the disk of oak
has its firmest wood at the center, and each successive piece from the
center outward is lighter than its neighbor.
Examining the pieces, this difference is not as readily explained by
the appearance of each piece as in the case of pine wood.
Nevertheless, one conspicuous point appears at once. The pores, so
very distinct in oak, are very minute in the wood near the center, and
thus the wood is far less porous.
Studying different trees, it is found that in the pines, wood with
narrow rings is just as heavy as and often heavier than the wood with
wider rings; but if the rings are unusually narrow in any part of the
disk, the wood has a lighter color; that is, there is less summer-wood
and therefore less weight.
In oak, ash, or elm trees of thrifty growth, the rings, fairly wide
(not less than one-twelfth inch), always form the heaviest wood, while
any piece with very narrow rings is light. On the other hand, the
weight of a piece of hard maple or birch is quite independent of the
width of its rings.
The bases of limbs (knots) are usually heavy, very heavy in conifers,
and also the wood which surrounds them, but generally the wood of the
limbs is lighter than that of the stem, and the wood of the roots is
the lightest.
In general, it may be said that none of the native woods in common use
in this country are when dry as heavy as water, _i.e._, sixty-two
pounds to the cubic foot. Few exceed fifty pounds, while most of them
fall below forty pounds, and much of the pine and other coniferous
wood weigh less than thirty pounds per cubic foot. The weight of the
wood is in itself an important quality. Weight assists in
distinguishing maple from poplar. Lightness coupled with great
strength and stiffness recommends wood for a thousand different uses.
To a large extent weight predicates the strength of the wood, at least
in the same species, so that a heavy piece of oak will exceed in
strength a light piece of the same species, and in pine it appears
probable that, weight for weight, the strength of the wood of various
pines is nearly equal.
WEIGHT OF KILN-DRIED WOOD OF DIFFERENT SPECIES
-----------------------------------------+----------------------------
| Approximate
|----------+-----------------
| | Weight of
| |---------+-------
Species | Specific | 1 | 1,000
| Weight | Cubic | Feet
| | Foot | Lumber
-----------------------------------------+----------+---------+-------
(_a_) Very Heavy Woods: | | |
Hickory, Oak, Persimmon, Osage Orange, | | |
Black Locust, Hackberry, Blue Beech, | | |
best of Elm and Ash |0.70-0.80 | 42-48 | 3,700
(_b_) Heavy Woods | | |
Ash, Elm, Cherry, Birch, Maple, Beech, | | |
Walnut, Sour Gum, Coffee Tree, Honey | | |
Locust, best of Southern Pine and | | |
Tamarack |0.60-0.70 | 36-42 | 3,200
(_c_) Woods of Medium Weight: | | |
Southern Pine, Pitch Pine, Tamarack, | | |
Douglas Spruce, Western Hemlock, | | |
Sweet Gum, Soft Maple, Sycamore, | | |
Sassafras, Mulberry, light grades of | | |
Birch and Cherry |0.50-0.60 | 30-36 | 2,700
(_d_) Light Woods: | | |
Norway and Bull Pine, Red Cedar, | | |
Cypress, Hemlock, the Heavier Spruces | | |
and Firs, Redwood, Basswood, Chestnut, | | |
Butternut, Tulip, Catalpa, Buckeye, | | |
heavier grades of Poplar |0.40-0.50 | 24-30 | 2,200
(_e_) Very Light Woods: | | |
White Pine, Spruce, Fir, White Cedar, | | |
Poplar |0.30-0.40 | 18-24 | 1,800
-----------------------------------------+----------+---------+-------
"FIGURE" IN WOOD
Many theories have been propounded as to the cause of "figure" in
timber; while it is true that all timber possesses "figure" in some
degree, which is more noticeable if it be cut in certain ways, yet
there are some woods in which it is more conspicuous than in others,
and which for cabinet or furniture work are much appreciated, as it
adds to the value of the work produced.
The characteristic "figure" of oak is due to the broad and deep
medullary rays so conspicuous in this timber, and the same applies to
honeysuckle. Figure due to the same cause is found in sycamore and
beech, but is not so pronounced. The beautiful figure in "bird's eye
maple" is supposed to be due to the boring action of insects in the
early growth of the tree, causing pits or grooves, which in time
become filled up by being overlain by fresh layers of wood growth;
these peculiar and unique markings are found only in the older and
inner portion of the tree.
Pitch pine has sometimes a very beautiful "figure," but it generally
does not go deep into the timber; walnut has quite a variety of
"figures," and so has the elm. It is in mahogany, however, that we
find the greatest variety of "figure," and as this timber is only used
for furniture and fancy work, a good "figure" greatly enhances its
value, as firmly figured logs bring fancy prices.
Mahogany, unlike the oak, never draws its "figure" from its small and
almost unnoticeable medullary rays, but from the twisted condition of
its fibres; the natural growth of mahogany produces a straight wood;
what is called "figured" is unnatural and exceptional, and thus adds
to its value as an ornamental wood. These peculiarities are rarely
found in the earlier portion of the tree that is near the center,
being in this respect quite different from maple; they appear when the
tree is more fully developed, and consist of bundles of woody fibres
which, instead of being laid in straight lines, behave in an erratic
manner and are deposited in a twisted form; sometimes it may be caused
by the intersection of branches, or possibly by the crackling of the
bark pressing on the wood, and thus moving it out of its natural
straight course, causing a wavy line which in time becomes
accentuated.
It will have been observed by most people that the outer portion of a
tree is often indented by the bark, and the outer rings often follow a
sinuous course which corresponds to this indention, but in most trees,
after a few years, this is evened up and the annual rings assume their
nearly circular form; it is supposed by some that in the case of
mahogany this is not the case, and that the indentations are even
accentuated.
The best figured logs of timber are secured from trees which grow in
firm rocky soil; those growing on low-lying or swampy ground are
seldom figured. To the practical woodworker the figure in mahogany
causes some difficulty in planing the wood to a smooth surface; some
portions plane smooth, others are the "wrong way of the grain."
Figure in wood is effected by the way light is thrown upon it, showing
light if seen from one direction, and dark if viewed from another, as
may easily be observed by holding a piece of figured mahogany under
artificial light and looking at it from opposite directions. The
characteristic markings on mahogany are "mottle," which is also found
in sycamore, and is conspicuous on the backs of fiddles and violins,
and is not in itself valuable; it runs the transverse way of the
fibres and is probably the effect of the wind upon the tree in its
early stages of growth. "Roe," which is said to be caused by the
contortion of the woody fibres, and takes a wavy line parallel to
them, is also found in the hollow of bent stems and in the root
structure, and when combined with "mottle" is very valuable. "Dapple"
is an exaggerated form of mottle. "Thunder shake," "wind shake," or
"tornado shake" is a rupture of the fibres across the grain, which in
mahogany does not always break them; the tree swaying in the wind only
strains its fibres, and thus produces mottle in the wood.
SECTION V
ENEMIES OF WOOD
From the writer's personal investigations of this subject in different
sections of the country, the damage to forest products of various
kinds from this cause seems to be far more extensive than is generally
recognized. Allowing a loss of five per cent on the total value of the
forest products of the country, which the writer believes to be a
conservative estimate, it would amount to something over $30,000,000
annually. This loss differs from that resulting from insect damage to
natural forest resources, in that it represents more directly a loss
of money invested in material and labor. In dealing with the insects
mentioned, as with forest insects in general, the methods which yield
the best results are those which relate directly to preventing attack,
as well as those which are unattractive or unfavorable. The insects
have two objects in their attack: one is to obtain food, the other is
to prepare for the development of their broods. Different species of
insects have special periods during the season of activity (March to
November), when the adults are on the wing in search of suitable
material in which to deposit their eggs. Some species, which fly in
April, will be attracted to the trunks of recently felled pine trees
or to piles of pine sawlogs from trees felled the previous winter.
They are not attracted to any other kind of timber, because they can
live only in the bark or wood of pine, and only in that which is in
the proper condition to favor the hatching of their eggs and the
normal development of their young. As they fly only in April, they
cannot injure the logs of trees felled during the remainder of the
year.
There are also oak insects, which attack nothing but oak; hickory,
cypress, and spruce insects, etc., which have different habits and
different periods of flight, and require special conditions of the
bark and wood for depositing their eggs or for subsequent development
of their broods. Some of these insects have but one generation in a
year, others have two or more, while some require more than one year
for the complete development and transformation. Some species deposit
their eggs in the bark or wood of trees soon after they are felled or
before any perceptible change from the normal living tissue has taken
place; other species are attracted only to dead bark and dead wood of
trees which have been felled or girdled for several months; others are
attracted to dry and seasoned wood; while another class will attack
nothing but very old, dry bark or wood of special kinds and under
special conditions. Thus it will be seen how important it is for the
practical man to have knowledge of such of the foregoing facts as
apply to his immediate interest in the manufacture or utilization of a
given forest product, in order that he may with the least trouble and
expense adjust his business methods to meet the requirements for
preventing losses.
The work of different kinds of insects, as represented by special
injuries to forest products, is the first thing to attract attention,
and the distinctive character of this work is easily observed, while
the insect responsible for it is seldom seen, or it is so difficult to
determine by the general observer from descriptions or illustrations
that the species is rarely recognized. Fortunately, the character of
the work is often sufficient in itself to identify the cause and
suggest a remedy, and in this section primary consideration is given
to this phase of the subject.
Ambrosia or Timber Beetles
[Illustration: Fig. 22. Work of Ambrosia Beetles in Tulip or
Yellow Poplar Wood. _a_, work of _Xyleborus affinis_ and
_Xyleborus inermis_; _b_, _Xyleborus obesus_ and work; _c_,
bark; _d_, sapwood; _e_, heartwood.]
[Illustration: Fig. 23. Work of Ambrosia Beetles in Oak. _a_,
_Monarthrum mali_ and work; _b_, _Platypus compositus_ and
work; _c_, bark; _d_, sapwood; _e_, heartwood; _f_, character
of work in wood from injured log.]
The characteristic work of this class of wood-boring beetles is shown
in Figs. 22 and 23. The injury consists of pinhole and stained-wood
defects in the sapwood and heartwood of recently felled or girdled
trees, sawlogs, pulpwood, stave and shingle bolts, green or
unseasoned lumber, and staves and heads of barrels containing
alcoholic liquids. The holes and galleries are made by the adult
parent beetles, to serve as entrances and temporary houses or
nurseries for the development of their broods of young, which feed on
a fungus growing on the walls of the galleries.
The growth of this ambrosia-like fungus is induced and controlled by
the parent beetles, and the young are dependent upon it for food. The
wood must be in exactly the proper condition for the growth of the
fungus in order to attract the beetles and induce them to excavate
their galleries; it must have a certain degree of moisture and other
favorable qualities, which usually prevail during the period involved
in the change from living, or normal, to dead or dry wood; such a
condition is found in recently felled trees, sawlogs, or like crude
products.
There are two general types or classes of these galleries: one in
which the broods develop together in the main burrows (see Fig. 22),
the other in which the individuals develop in short, separate side
chambers, extending at right angles from the primary galleries (see
Fig. 23). The galleries of the latter type are usually accompanied by
a distinct staining of the wood, while those of the former are not.
The beetles responsible for this work are cylindrical in form,
apparently with a head (the prothorax) half as long as the remainder
of the body (see Figs. 22, _a_, and 23, _a_).
North American species vary in size from less than one-tenth to
slightly more than two-tenths of an inch, while some of the
subtropical and tropical species attain a much larger size. The
diameter of the holes made by each species corresponds closely to that
of the body, and varies from about one-twentieth to one-sixteenth of
an inch for the tropical species.
Round-headed Borers
[Illustration: Fig. 24. Work of Round-headed and Flat-headed
Borers in Pine. _a_, work of round-headed borer, "sawyer,"
_Monohammus spiculatus_, natural size _b_, _Ergates
spiculatus_; _c_, work of flat-headed borer, _Buprestis_,
larva and adult; _d_, bark; _e_, sapwood; _f_, heartwood.]
The character of the work of this class of wood- and bark-boring grubs
is shown in Fig. 24. The injuries consist of irregular flattened or
nearly round wormhole defects in the wood, which sometimes result in
the destruction of valuable parts of the wood or bark material. The
sapwood and heartwood of recently felled trees, sawlogs, poles posts,
mine props, pulpwood and cordwood, also lumber or square timber, with
bark on the edges, and construction timber in new and old buildings,
are injured by wormhole defects, while the valuable parts of stored
oak and hemlock tanbark and certain kinds of wood are converted into
worm-dust. These injuries are caused by the young or larvae of
long-horned beetles. Those which infest the wood hatch from eggs
deposited in the outer bark of logs and like material, and the minute
grubs hatching therefrom bore into the inner bark, through which they
extend their irregular burrows, for the purpose of obtaining food from
the sap and other nutritive material found in the plant tissue. They
continue to extend and enlarge their burrows as they increase in size,
until they are nearly or quite full grown. They then enter the wood
and continue their excavations deep into the sapwood or heartwood
until they attain their normal size. They then excavate pupa cells in
which to transform into adults, which emerge from the wood through
exit holes in the surface. This class of borers is represented by a
large number of species. The adults, however, are seldom seen by the
general observer unless cut out of the wood before they have emerged.
Flat-headed Borers
The work of the flat-headed borers (Fig. 24) is only distinguished
from that of the preceding by the broad, shallow burrows, and the much
more oblong form of the exit holes. In general, the injuries are
similiar, and effect the same class of products, but they are of much
less importance. The adult forms are flattened, metallic-colored
beetles, and represent many species, of various sizes.
Timber Worms
[Illustration: Fig. 25. Work of Timber Worms in Oak. _a_,
work of oak timber worm, _Eupsalis minuta_; _b_, barked
surface; _c_, bark; _d_, sapwood timber worm, _Hylocoetus
lugubris_, and work; _e_, sapwood.]
The character of the work done by this class is shown in Fig. 25. The
injury consists of pinhole defects in the sapwood and heartwood of
felled trees, sawlogs and like material which have been left in the
woods or in piles in the open for several months during the warmer
seasons. Stave and shingle bolts and closely piled oak lumber and
square timbers also suffer from injury of this kind. These injuries
are made by elongate, slender worms or larvae, which hatch from eggs
deposited by the adult beetles in the outer bark, or, where there is
no bark, just beneath the surface of the wood. At first the young
larvae bore almost invisible holes for a long distance through the
sapwood and heartwood, but as they increase in size the same holes are
enlarged and extended until the larvae have attained their full
growth. They then transform to adults, and emerge through the enlarged
entrance burrows. The work of these timber worms is distinguished from
that of the timber beetles by the greater variation in the size of
holes in the same piece of wood, also by the fact that they are not
branched from a single entrance or gallery, as are those made by the
beetles.
[Illustration: Fig. 26. Work of Powder Post Beetle,
_Sinoxylon basilare_, in Hickory Poles, showing Transverse
Egg Galleries excavated by the Adult, _a_, entrance; _b_,
gallery; _c_, adult.]
[Illustration: Fig. 27. Work of Powder
Post Beetle, _Sinoxylon basilare_, in Hickory Pole. _a_,
character of work by larvae; _b_, exit holes made by
emerging broods.]
Powder Post Borers
The character of the work of this class of insects is shown in Figs.
26, 27, and 28. The injury consists of closely placed burrows, packed
with borings, or a completely destroyed or powdered condition of the
wood of seasoned products, such as lumber, crude and finished handle
and wagon stock, cooperage and wooden truss hoops, furniture, and
inside finish woodwork, in old buildings, as well as in many other
crude or finished and utilized woods. This is the work of both the
adults and young stages of some species, or of the larval stage alone
of others. In the former, the adult beetles deposit their eggs in
burrows or galleries excavated for the purpose, as in Figs. 26 and 27,
while in the latter (Fig. 28) the eggs are on or beneath the surface
of the wood. The grubs complete the destruction by boring through the
solid wood in all directions and packing their burrows with the
powdered wood. When they are full grown they transform to the adult,
and emerge from the injured material through holes in the surface.
Some of the species continue to work in the same wood until many
generations have developed and emerged or until every particle of wood
tissue has been destroyed and the available nutritive substance
extracted.
[Illustration: Fig. 28. Work of Powder Post Beetles, _Lyctus
striatus_, in Hickory Handles and Spokes. _a_, larva; _b_,
pupa; _c_, adult; _d_, exit holes; _e_, entrance of larvae
(vents for borings are exits of parasites); _f_, work of
larvae; _g_, wood, completely destroyed; _h_, sapwood; _i_,
heartwood.]
Conditions Favorable for Insect
Injury--Crude Products--Round Timber with Bark on
Newly felled trees, sawlogs, stave and heading bolts, telegraph poles,
posts, and the like material, cut in the fall and winter, and left on
the ground or in close piles during a few weeks or months in the
spring or summer, causing them to heat and sweat, are especially
liable to injury by ambrosia beetles (Figs. 22 and 23), round and
flat-headed borers (Fig. 24), and timber worms (Fig. 25), as are also
trees felled in the warm season, and left for a time before working up
into lumber.
The proper degree of moisture found in freshly cut living or dying
wood, and the period when the insects are flying, are the conditions
most favorable for attack. This period of danger varies with the time
of the year the timber is felled and with the different kinds of
trees. Those felled in late fall and winter will generally remain
attractive to ambrosia beetles, and to the adults of round- and
flat-headed borers during March, April, and May. Those felled in April
to September may be attacked in a few days after they are felled, and
the period of danger may not extend over more than a few weeks.
Certain kinds of trees felled during certain months and seasons are
never attacked, because the danger period prevails only when the
insects are flying; on the other hand, if the same kinds of trees are
felled at a different time, the conditions may be most attractive when
the insects are active, and they will be thickly infested and ruined.
The presence of bark is absolutely necessary for infestation by most
of the wood-boring grubs, since the eggs and young stages must occupy
the outer and inner portions before they can enter the wood. Some
ambrosia and timber worms will, however, attack barked logs,
especially those in close piles, and others shaded and protected from
rapid drying.
The sapwood of pine, spruce, fir, cedar, cypress, and the like
softwoods is especially liable to injury by ambrosia beetles, while
the heartwood is sometimes ruined by a class of round-headed borers,
known as "sawyers." Yellow poplar, oak, chestnut, gum, hickory, and
most other hardwoods are as a rule attacked by species of ambrosia
beetles, sawyers, and timber worms, different from those infesting the
pines, there being but very few species which attack both.
Mahogany and other rare and valuable woods imported from the tropics
to this country in the form of round logs, with or without bark on,
are commonly damaged more or less seriously by ambrosia beetles and
timber worms.
It would appear from the writer's investigations of logs received at
the mills in this country, that the principal damage is done during a
limited period--from the time the trees are felled until they are
placed in fresh or salt water for transportation to the shipping
points. If, however, the logs are loaded on a vessel direct from the
shore, or if not left in the water long enough to kill the insects,
the latter will continue their destructive work during transportation
to other countries and after they arrive, and until cold weather
ensues or the logs are converted into lumber.
It was also found that a thorough soaking in sea-water, while it
usually killed the insects at the time, did not prevent subsequent
attacks by both foreign and native ambrosia beetles; also, that the
removal of the bark from such logs previous to immersion did not
render them entirely immune. Those with the bark off were attacked
more than those with it on, owing to a greater amount of saline
moisture retained by the bark.
How to Prevent Injury
From the foregoing it will be seen that some requisites for preventing
these insect injuries to round timber are:
1. To provide for as little delay as possible between the
felling of the tree and its manufacture into rough products.
This is especially necessary with trees felled from April to
September, in the region north of the Gulf States, and from
March to November in the latter, while the late fall and
winter cutting should all be worked up by March or April.
2. If the round timber must be left in the woods or on the
skidways during the danger period, every precaution should
be taken to facilitate rapid drying of the inner bark, by
keeping the logs off the ground in the sun, or in loose
piles; or else the opposite extreme should be adopted and
the logs kept in water.
3. The immediate removal of all the bark from poles, posts,
and other material which will not be seriously damaged by
checking or season checks.
4. To determine and utilize the proper months or seasons to
girdle or fell different kinds of trees: Bald cypress in the
swamps of the South are "girdled" in order that they may
die, and in a few weeks or months dry out and become light
enough to float. This method has been extensively adopted in
sections where it is the only practicable one by which the
timber can be transported to the sawmills. It is found,
however, that some of these "girdled" trees are especially
attractive to several species of ambrosia beetles (Figs. 22
and 23), round-headed borers (Fig. 24) and timber worms
(Fig. 25), which cause serious injury to the sapwood or
heartwood, while other trees "girdled" at a different time
or season are not injured. This suggested to the writer the
importance of experiments to determine the proper time to
"girdle" trees to avoid losses, and they are now being
conducted on an extensive scale by the United States Forest
Service, in co-operation with prominent cypress operators in
different sections of the cypress-growing region.
Saplings
Saplings, including hickory and other round hoop-poles and similiar
products, are subject to serious injuries and destruction by round-
and flat-headed borers (Fig. 24), and certain species of powder post
borers (Figs. 26 and 27) before the bark and wood are dead or dry, and
also by other powder post borers (Fig. 28) after they are dried and
seasoned. The conditions favoring attack by the former class are those
resulting from leaving the poles in piles or bundles in or near the
forest for a few weeks during the season of insect activity, and by
the latter from leaving them stored in one place for several months.
Stave, Heading and Shingle Bolts
These are attacked by ambrosia beetles (Figs. 22 and 23), and the oak
timber worm (Fig. 25, _a_), which, as has been frequently reported,
cause serious losses. The conditions favoring attack by these insects
are similiar to those mentioned under "Round Timber." The insects may
enter the wood before the bolts are cut from the log or afterward,
especially if the bolts are left in moist, shady places in the woods,
in close piles during the danger period. If cut during the warm
season, the bark should be removed and the bolts converted into the
smallest practicable size and piled in such manner as to facilitate
rapid drying.
Unseasoned Products in the Rough
Freshly sawn hardwood, placed in close piles during warm, damp weather
in July and September, presents especially favorable conditions for
injury by ambrosia beetles (Figs. 22, _a_, and 23, _a_). This is due
to the continued moist condition of such material.
Heavy two-inch or three-inch stuff is also liable to attack even in
loose piles with lumber or cross sticks. An example of the latter was
found in a valuable lot of mahogany lumber of first grade, the value
of which was reduced two thirds by injury from a native ambrosia
beetle. Numerous complaints have been received from different sections
of the country of this class of injury to oak, poplar, gum, and other
hardwoods. In all cases it is the moist condition and retarded drying
of the lumber which induces attack; therefore, any method which will
provide for the rapid drying of the wood before or after piling will
tend to prevent losses.
It is important that heavy lumber should, as far as possible, be cut
in the winter months and piled so that it will be well dried out
before the middle of March. Square timber, stave and heading bolts,
with the bark on, often suffer from injuries by flat- or round-headed
borers, hatching from eggs deposited in the bark of the logs before
they are sawed and piled. One example of serious damage and loss was
reported in which white pine staves for paint buckets and other small
wooden vessels, which had been sawed from small logs, and the bark
left on the edges, were attacked by a round-headed borer, the adults
having deposited their eggs in the bark after the stock was sawn and
piled. The character of the injury is shown in Fig. 29. Another
example was reported from a manufacturer in the South, where the
pieces of lumber which had strips of bark on one side were seriously
damaged by the same kind of borer, the eggs having been deposited in
the logs before sawing or in the bark after the lumber was piled. If
the eggs are deposited in the logs, and the borers have entered the
inner bark or the wood before sawing, they may continue their work
regardless of methods of piling, but if such lumber is cut from new
logs and placed in the pile while green, with the bark surface up, it
will be much less liable to attack than if piled with the bark edges
down. This liability of lumber with bark edges or sides to be attacked
by insects suggests the importance of the removal of the bark, to
prevent damage, or, if this is not practicable, the lumber with the
bark on the sides should be piled in open, loose piles with the bark
up, while that with the bark on the edges should be placed on the
outer edges of the piles, exposed to the light and air.
[Illustration: Fig. 29. Work of Round-headed Borers,
_Callidium antennatum_, in White Pine Bucket Staves from New
Hampshire. _a_, where egg was deposited in bark; _b_, larval
mine; _c_, pupal cell; _d_, exit in bark; _e_, adult.]
In the Southern States it is difficult to keep green timber in the
woods or in piles for any length of time, because of the rapidity
which wood-destroying fungi attack it. This is particularly true
during the summer season, when the humidity is greatest. There is
really no easily-applied, general specific for these summer troubles
in the handling of wood, but there are some suggestions that are worth
while that it may be well to mention. One of these, and the most
important, is to remove all the bark from the timber that has been
cut, just as soon as possible after felling. And, in this, emphasis
should be laid on the ALL, as a piece of bark no larger than a man's
little finger will furnish an entering place for insects, and once
they get in, it is a difficult matter to get rid of them, for they
seldom stop boring until they ruin the stick. And again, after the
timber has been felled and the bark removed, it is well to get it to
the mill pond or cut up into merchantable sizes and on to the pile as
soon as possible. What is wanted is to get the timber up off the
ground, to a place where it can get plenty of air, to enable the sap
to dry up before it sours; and, besides, large units of wood are more
likely to crack open on the ends from the heat than they would if cut
up into the smaller units for merchandizing.
A moist condition of lumber and square timber, such as results from
close or solid piles, with the bottom layers on the ground or on
foundations of old decaying logs or near decaying stumps and logs,
offers especially favorable conditions for the attack of white ants.
Seasoned Products in the Rough
Seasoned or dry timber in stacks or storage is liable to injury by
powder post borers (Fig. 28). The conditions favoring attack are: (1)
The presence of a large proportion of sapwood, as in hickory, ash, and
similiar woods; (2) material which is two or more years old, or that
which has been kept in one place for a long time; (3) access to old
infested material. Therefore, such stock should be frequently examined
for evidence of the presence of these insects. This is always
indicated by fine, flour-like powder on or beneath the piles, or
otherwise associated with such material. All infested material should
be at once removed and the infested parts destroyed by burning.
Dry Cooperage Stock and Wooden Truss Hoops
These are especially liable to attack and serious injury by powder
post borers (Fig. 28), under the same or similiar conditions as the
preceding.
Staves and Heads of Barrels containing Alcoholic Liquids
These are liable to attack by ambrosia beetles (Figs. 22, _a_, and 23,
_a_), which are attracted by the moist condition and possibly by the
peculiar odor of the wood, resembling that of dying sapwood of trees
and logs, which is their normal breeding place.
There are many examples on record of serious losses of liquors from
leakage caused by the beetles boring through the staves and heads of
the barrels and casks in cellars and storerooms.
The condition, in addition to the moisture of the wood, which is
favorable for the presence of the beetles, is proximity to their
breeding places, such as the trunks and stumps of recently felled or
dying oak, maple, and other hardwood or deciduous trees; lumber yards,
sawmills, freshly-cut cordwood, from living or dead trees, and forests
of hardwood timber. Under such conditions the beetles occur in great
numbers, and if the storerooms and cellars in which the barrels are
kept stored are damp, poorly ventilated, and readily accessible to
them, serious injury is almost certain to follow.
SECTION VI
WATER IN WOOD
DISTRIBUTION OF WATER IN WOOD
Local Distribution of Water in Wood
As seasoning means essentially the more or less rapid evaporation of
water from wood, it will be necessary to discuss at the very outset
where water is found in wood, and its local seasonal distribution in a
tree.
Water may occur in wood in three conditions: (1) It forms the greater
part (over 90 per cent) of the protoplasmic contents of the living
cells; (2) it saturates the walls of all cells; and (3) it entirely or
at least partly fills the cavities of the lifeless cells, fibres, and
vessels.
In the sapwood of pine it occurs in all three forms; in the heartwood
only in the second form, it merely saturates the walls.
Of 100 pounds of water associated with 100 pounds of dry wood
substance taken from 200 pounds of fresh sapwood of white pine, about
35 pounds are needed to saturate the cell walls, less than 5 pounds
are contained in the living cells, and the remaining 60 pounds partly
fill the cavities of the wood fibres. This latter forms the sap as
ordinarily understood.
The wood next to the bark contains the most water. In the species
which do not form heartwood, the decrease toward the pith is gradual,
but where heartwood is formed the change from a more moist to a drier
condition is usually quite abrupt at the sapwood limit.
In long-leaf pine, the wood of the outer one inch of a disk may
contain 50 per cent of water, that of the next, or the second inch,
only 35 per cent, and that of the heartwood, only 20 per cent. In
such a tree the amount of water in any one section varies with the
amount of sapwood, and is greater for the upper than the lower cuts,
greater for the limbs than the stems, and greatest of all in the
roots.
Different trees, even of the same kind and from the same place, differ
as to the amount of water they contain. A thrifty tree contains more
water than a stunted one, and a young tree more than on old one, while
the wood of all trees varies in its moisture relations with the season
of the year.
Seasonal Distribution of Water in Wood
It is generally supposed that trees contain less water in winter than
in summer. This is evidenced by the popular saying that "the sap is
down in the winter." This is probably not always the case; some trees
contain as much water in winter as in summer, if not more. Trees
normally contain the greatest amount of water during that period when
the roots are active and the leaves are not yet out. This activity
commonly begins in January, February, and March, the exact time
varying with the kind of timber and the local atmospheric conditions.
And it has been found that green wood becomes lighter or contains less
water in late spring or early summer, when transpiration through the
foliage is most rapid. The amount of water at any one season, however,
is doubtless much influenced by the amount of moisture in the soil.
The fact that the bark peels easily in the spring depends on the
presence of incomplete, soft tissue found between wood and bark during
this season, and has little to do with the total amount of water
contained in the wood of the stem.
Even in the living tree a flow of sap from a cut occurs only in
certain kinds of trees and under special circumstances. From boards,
felled timber, etc., the water does not flow out, as is sometimes
believed, but must be evaporated. The seeming exceptions to this rule
are mostly referable to two causes; clefts or "shakes" will allow
water contained in them to flow out, and water is forced out of sound
wood, if very sappy, whenever the wood is warmed, just as water flows
from green wood when put in a stove.
Composition of Sap
The term "sap" is an ambiguous expression. The sap in the tree
descends through the bark, and except in early spring is not present
in the wood of the tree except in the medullary rays and living
tissues in the "sapwood."
What flows through the "sapwood" is chiefly water brought from the
soil. It is not pure water, but contains many substances in solution,
such as mineral salts, and in certain species--maple, birch, etc., it
also contains at certain times a small percentage of sugar and other
organic matter.
The water rises from the roots through the sapwood to the leaves,
where it is converted into true "sap" which descends through the bark
and feeds the living tissues between the bark and the wood, which
tissues make the annual growth of the trunk. The wood itself contains
very little true sap and the heartwood none.
The wood contains, however, mineral substances, organic acids,
volatile oils and gums, as resin, cedar oil, etc.
All the conifers--pines, cedars, junipers, cypresses, sequoias, yews,
and spruces--contain resin. The sap of deciduous trees--those which
shed their leaves at stated seasons--is lacking in this element, and
its constituents vary greatly in the different species. But there is
one element common to all trees, and for that matter to almost all
plant growth, and that is albumen.
Both resin and albumen, as they exist in the sap of woods, are soluble
in water; and both harden with heat, much the same as the white of an
egg, which is almost pure albumen.
These organic substances are the dissolved reserve food, stored during
the winter in the pith rays, etc., of the wood and bark; generally but
a mere trace of them is to be found. From this it appears that the
solids contained in the sap, such as albumen, gum, sugar, etc.,
cannot exercise the influence on the strength of the wood which is so
commonly claimed for them.
Effects of Moisture on Wood
The question of the effect of moisture upon the strength and stiffness
of wood offers a wide scope for study, and authorities consulted
differ in conclusions. Two authorities give the tensile strength in
pounds per square inch for white oak as 10,000 and 19,500,
respectively; for spruce, 8,000 to 19,500, and other species in
similiar startling contrasts.
Wood, we are told, is composed of organic products. The chief material
is cellulose, and this in its natural state in the living plant or
green wood contains from 25 to 35 per cent of its weight in moisture.
The moisture renders the cellulose substance pliable. What the
physical action of the water is upon the molecular structure of
organic material, to render it softer and more pliable, is largely a
matter of conjecture.
The strength of a timber depends not only upon its relative freedom
from imperfections, such as knots, crookedness of grain, decay,
wormholes or ring-shakes, but also upon its density; upon the rate at
which it grew, and upon the arrangement of the various elements which
compose it.
The factors effecting the strength of wood are therefore of two
classes: (1) Those inherent in the wood itself and which may cause
differences to exist between two pieces from the same species of wood
or even between the two ends of a piece, and (2) those which are
foreign to the wood itself, such as moisture, oils, and heat.
Though the effect of moisture is generally temporary, it is far more
important than is generally realized. So great, indeed, is the effect
of moisture that under some conditions it outweighs all the other
causes which effect strength, with the exception, perhaps of decided
imperfections in the wood itself.
The Fibre Saturation Point in Wood
Water exists in green wood in two forms: (1) As liquid water contained
in the cavities of the cells or pores, and (2) as "imbibed" water
intimately absorbed in the substance of which the wood is composed.
The removal of the free water from the cells or pores will evidently
have no effect upon the physical properties or shrinkage of the wood,
but as soon as any of the "imbibed" moisture is removed from the cell
walls, shrinkage begins to take place and other changes occur. The
strength also begins to increase at this time.
The point where the cell walls or wood substance becomes saturated is
called the "fibre saturation point," and is a very significant point
in the drying of wood.
It is easy to remove the free water from woods which will stand a high
temperature, as it is only necessary to heat the wood slightly above
the boiling point in a closed vessel, which will allow the escape of
the steam as it is formed, but will not allow dry air to come in
contact with the wood, so that the surface will not become dried below
its saturation point. This can be accomplished with most of the
softwoods, but not as a rule with the hardwoods, as they are injured
by the temperature necessary.
The chief difficulties are encountered in evaporating the "imbibed"
moisture and also where the free water has to be removed through its
gradual transfusion instead of boiling. As soon as the imbibed
moisture begins to be extracted from any portion, shrinkage takes
place and stresses are set up in the wood which tend to cause
checking.
The fibre saturation point lies between moisture conditions of 25 and
30 per cent of the dry weight of the wood, depending on the species.
Certain species of eucalyptus, and probably other woods, however,
appear to be exceptional in this respect, in that shrinkage begins to
take place at a moisture condition of 80 to 90 per cent of the dry
weight.
SECTION VII
WHAT SEASONING IS
Seasoning is ordinarily understood to mean drying. When exposed to the
sun and air, the water in green wood rapidly evaporates. The rate of
evaporation will depend on: (1) the kind of wood; (2) the shape and
thickness of the timber; and (3) the conditions under which the wood
is placed or piled.
Pieces of wood completely surrounded by air, exposed to the wind and
the sun, and protected by a roof from rain and snow, will dry out very
rapidly, while wood piled or packed close together so as to exclude
the air, or left in the shade and exposed to rain and snow, will dry
out very slowly and will also be subject to mould and decay.
But seasoning implies other changes besides the evaporation of water.
Although we have as yet only a vague conception as to the exact nature
of the difference between seasoned and unseasoned wood, it is very
probable that one of these consists in changes in the albuminous
substances in the wood fibres, and possibly also in the tannins,
resins, and other incrusting substances. Whether the change in these
substances is merely a drying-out, or whether it consists in a partial
decomposition is at yet undetermined. That the change during the
seasoning process is a profound one there can be no doubt, because
experience has shown again and again that seasoned wood fibre is very
much more permeable, both for liquids and gases than the living,
unseasoned fibre.
One can picture the albuminous substances as forming a coating which
dries out and possibly disintegrates when the wood dries. The
drying-out may result in considerable shrinkage, which may make the
wood fibre more porous. It is also possible that there are oxidizing
influences at work within these substances which result in their
disintegration. Whatever the exact nature of the change may be, one
can say without hesitation that exposure to the wind and air brings
about changes in the wood, which are of such a nature that the wood
becomes drier and more permeable.
When seasoned by exposure to live steam, similiar changes may take
place; the water leaves the wood in the form of steam, while the
organic compounds in the walls probably coagulate or disintegrate
under the high temperature.
The most effective seasoning is without doubt that obtained by the
uniform, slow drying which takes place in properly constructed piles
outdoors, under exposure to the winds and the sun and under cover from
the rain and snow, and is what has been termed "air-seasoning." By
air-seasoning oak and similiar hardwoods, nature performs certain
functions that cannot be duplicated by any artificial means. Because
of this, woods of this class cannot be successfully kiln-dried green
from the saw.
In drying wood, the free water within the cells passes through the
cell walls until the cells are empty, while the cell walls remain
saturated. When all the free water has been removed, the cell walls
begin to yield up their moisture. Heat raises the absorptive power of
the fibres and so aids the passage of water from the interior of the
cells. A confusion in the word "sap" is to be found in many
discussions of kiln-drying; in some instances it means water, in other
cases it is applied to the organic substances held in a water solution
in the cell cavities. The term is best confined to the organic
substances from the living cell. These substances, for the most part
of the nature of sugar, have a strong attraction for water and water
vapor, and so retard drying and absorb moisture into dried wood. High
temperatures, especially those produced by live steam, appear to
destroy these organic compounds and therefore both to retard and to
limit the reabsorption of moisture when the wood is subsequently
exposed to the atmosphere.
Air-dried wood, under ordinary atmospheric temperatures, retains from
10 to 20 per cent of moisture, whereas kiln-dried wood may have no
more than 5 per cent as it comes from the kiln. The exact figures for
a given species depend in the first case upon the weather conditions,
and in the second case upon the temperature in the kiln and the time
during which the wood is exposed to it. When wood that has been
kiln-dried is allowed to stand in the open, it apparently ceases to
reabsorb moisture from the air before its moisture content equals that
of wood which has merely been air-dried in the same place, and under
the same conditions, in other words kiln-dried wood will not absorb as
much moisture as air-dried wood under the same conditions.
Difference between Seasoned and Unseasoned Wood
Although it has been known for a long time that there is a marked
difference in the length of life of seasoned and of unseasoned wood,
the consumers of wood have shown very little interest in its
seasoning, except for the purpose of doing away with the evils which
result from checking, warping, and shrinking. For this purpose both
kiln-drying and air-seasoning are largely in use.
The drying of material is a subject which is extremely important to
most industries, and in no industry is it of more importance than in
the lumber trade. Timber drying means not only the extracting of so
much water, but goes very deeply into the quality of the wood, its
workability and its cell strength, etc.
Kiln-drying, which dries the wood at a uniformly rapid rate by
artificially heating it in inclosed rooms, has become a part of almost
every woodworking industry, as without it the construction of the
finished product would often be impossible. Nevertheless much
unseasoned or imperfectly seasoned wood is used, as is evidenced by
the frequent shrinkage and warping of the finished articles. This is
explained to a certain extent by the fact that the manufacturer is
often so hard pressed for his product that he is forced to send out an
inferior article, which the consumer is willing to accept in that
condition rather than to wait several weeks or months for an article
made up of thoroughly seasoned material, and also that dry kilns are
at present constructed and operated largely without thoroughgoing
system.
Forms of kilns and mode of operation have commonly been copied by one
woodworking plant after the example of some neighboring establishment.
In this way it has been brought about that the present practices have
many shortcomings. The most progressive operators, however, have
experimented freely in the effort to secure special results desirable
for their peculiar products. Despite the diversity of practice, it is
possible to find among the larger and more enterprising operators a
measure of agreement, as to both methods and results, and from this to
outline the essentials of a correct theory. As a result, properly
seasoned wood commands a high price, and in some cases cannot be
obtained at all.
Wood seasoned out of doors, which by many is supposed to be much
superior to kiln-dried material, is becoming very scarce, as the
demand for any kind of wood is so great that it is thought not to pay
to hold it for the time necessary to season it properly. How long this
state of affairs is going to last it is difficult to say, but it is
believed that a reaction will come when the consumer learns that in
the long run it does not pay to use poorly seasoned material. Such a
condition has now arisen in connection with another phase of the
seasoning of wood; it is a commonly accepted fact that dry wood will
not decay nearly so fast as wet or green wood; nevertheless, the
immense superiority of seasoned over unseasoned wood for all purposes
where resistance to decay is necessary has not been sufficiently
recognized. In the times when wood of all kinds was both plentiful and
cheap, it mattered little in most cases how long it lasted or resisted
decay. Wood used for furniture, flooring, car construction, cooperage,
etc., usually got some chance to dry out before or after it was placed
in use. The wood which was exposed to decaying influences was
generally selected from those woods which, whatever their other
qualities might be, would resist decay longest.
To-day conditions have changed, so that wood can no longer be used to
the same extent as in former years. Inferior woods with less lasting
qualities have been pressed into service. Although haphazard methods
of cutting and subsequent use are still much in vogue, there are many
signs that both lumbermen and consumers are awakening to the fact that
such carelessness and wasteful methods of handling wood will no longer
do, and must give way to more exact and economical methods. The reason
why many manufacturers and consumers of wood are still using the older
methods is perhaps because of long custom, and because they have not
yet learned that, though the saving to be obtained by the application
of good methods has at all times been appreciable, now, when wood is
more valuable, a much greater saving is possible. The increased cost
of applying economical methods is really very slight, and is many
times exceeded by the value of the increased service which can be
secured through its use.
Manner of Evaporation of Water
The evaporation of water from wood takes place largely through the
ends, _i.e._, in the direction of the longitudinal axis of the wood
fibres. The evaporation from the other surfaces takes place very
slowly out of doors, and with greater rapidity in a dry kiln. The rate
of evaporation differs both with the kind of timber and its shape;
that is, thin material will dry more rapidly than heavier stock.
Sapwood dries faster than heartwood, and pine more rapidly than oak or
other hardwoods.
Tests made show little difference in the rate of evaporation in sawn
and hewn stock, the results, however, not being conclusive. Air-drying
out of doors takes from two months to a year, the time depending on
the kind of timber, its thickness, and the climatic conditions. After
wood has reached an air-dry condition it absorbs water in small
quantities after a rain or during damp weather, much of which is
immediately lost again when a few warm, dry days follow. In this way
wood exposed to the weather will continue to absorb water and lose it
for indefinite periods.
When soaked in water, seasoned woods absorb water rapidly. This at
first enters into the wood through the cell walls; when these are
soaked, the water will fill the cell lumen, so that if constantly
submerged the wood may become completely filled with water.
The following figures show the gain in weight by absorption of several
coniferous woods, air-dry at the start, expressed in per cent of the
kiln-dry weight:
ABSORPTION OF WATER BY DRY WOOD
---------------------------------------------------------------
| White Pine | Red Cedar | Hemlock | Tamarack
---------------------------------------------------------------
Air-dried | 108 | 109 | 111 | 108
Kiln-dried | 100 | 100 | 100 | 100
In water 1 day | 135 | 120 | 133 | 129
In water 2 days | 147 | 126 | 144 | 136
In water 3 days | 154 | 132 | 149 | 142
In water 4 days | 162 | 137 | 154 | 147
In water 5 days | 165 | 140 | 158 | 150
In water 7 days | 176 | 143 | 164 | 156
In water 9 days | 179 | 147 | 168 | 157
In water 11 days | 184 | 149 | 173 | 159
In water 14 days | 187 | 150 | 176 | 159
In water 17 days | 192 | 152 | 176 | 161
In water 25 days | 198 | 155 | 180 | 161
In water 30 days | 207 | 158 | 183 | 166
---------------------------------------------------------------
Rapidity of Evaporation
The rapidity with which water is evaporated, that is, the rate of
drying, depends on the size and shape of the piece and on the
structure of the wood. An inch board dries more than four times as
fast as a four-inch plank, and more than twenty times as fast as a
ten-inch timber. White pine dries faster than oak. A very moist piece
of pine or oak will, during one hour, lose more than four times as
much water per square inch from the cross-section, but only one half
as much from the tangential as from the radial section. In a long
timber, where the ends or cross-sections form but a small part of the
drying surface, this difference is not so evident. Nevertheless, the
ends dry and shrink first, and being opposed in this shrinkage by the
more moist adjoining parts, they check, the cracks largely
disappearing as seasoning progresses.
High temperatures are very effective in evaporating the water from
wood, no matter how humid the air, and a fresh piece of sapwood may
lose weight in boiling water, and can be dried to quite an extent in
hot steam.
In drying chemicals or fabrics, all that is required is to provide
heat enough to vaporize the moisture and circulation enough to carry
off the vapor thus secured, and the quickest and most economical means
to these ends may be used. While on the other hand, in drying wood,
whether in the form of standard stock or the finished product, the
application of the requisite heat and circulation must be carefully
regulated throughout the entire process, or warping and checking are
almost certain to result. Moreover, wood of different shapes and
thicknesses is very differently effected by the same treatment.
Finally, the tissues composing the wood, which vary in form and
physical properties, and which cross each other in regular directions,
exert their own peculiar influences upon its behavior during drying.
With our native woods, for instance, summer-wood and spring-wood show
distinct tendencies in drying, and the same is true in a less degree
of heartwood, as contrasted with sapwood. Or, again, pronounced
medullary rays further complicate the drying problem.
Physical Properties that influence Drying
The principal properties which render the drying of wood peculiarly
difficult are: (1) The irregular shrinkage; (2) the different ways in
which water is contained; (3) the manner in which moisture transfuses
through the wood from the center to the surface; (4) the plasticity of
the wood substance while moist and hot; (5) the changes which take
place in the hygroscopic and chemical nature of the surface; and (6)
the difference produced in the total shrinkage by different rates of
drying.
The shrinkage is unequal in different directions and in different
portions of the same piece. It is greatest in the circumferential
direction of the tree, being generally twice as great in this
direction as in the radial direction. In the longitudinal direction,
for most woods, it is almost negligible, being from 20 to over 100
times as great circumferentially as longitudinally.
There is a great variation in different species in this respect.
Consequently, it follows from necessity that large internal strains
are set up when the wood shrinks, and were it not for its plasticity
it would rupture. There is an enormous difference in the total amount
of shrinkage of different species of wood, varying from a shrinkage of
only 7 per cent in volume, based on the green dimensions, in the case
of some of the cedars to nearly 50 per cent in the case of some
species of eucalyptus.
When the free water in the capillary spaces of the wood fibre is
evaporated it follows the laws of evaporation from capillary spaces,
except that the passages are not all free passages, and much of the
water has to pass out by a process of transfusion through the moist
cell walls. These cell walls in the green wood completely surround the
cell cavities so that there are no openings large enough to offer a
passage to water or air.
The well-known "pits" in the cell walls extend through the secondary
thickening only, and not through the primary walls. This statement
applies to the tracheids and parenchyma cells in the conifer
(gymnosperms), and to the tracheids, parenchyma cells, and the wood
fibres in the broad-leaved trees (angiosperms); the vessels in the
latter, however, form open passages except when clogged by ingrowth
called tyloses, and the resin canals in the former sometimes form
occasional openings.
By heating the wood above the boiling point, corresponding to the
external pressure, the free water passes through the cell walls more
readily.
To remove the moisture from the wood substance requires heat in
addition to the latent heat of evaporation, because the molecules of
moisture are so intimately associated with the molecules, minute
particles composing the wood, that energy is required to separate them
therefrom.
Carefully conducted experiments show this to be from 16.6 to 19.6
calories per grain of dry wood in the case of beech, long-leaf pine,
and sugar maple.
The difficulty imposed in drying, however, is not so much the
additional heat required as it is in the rate at which the water
transfuses through the solid wood.
SECTION VIII
ADVANTAGES IN SEASONING
Three most important advantages of seasoning have already been made
apparent:
1. Seasoned timber lasts much longer than unseasoned. Since
the decay of timber is due to the attacks of wood-destroying
fungi, and since the most important condition of the growth
of these fungi is water, anything which lessens the amount
of water in wood aids in its preservation.
2. In the case of treated timber, seasoning before treatment
greatly increases the effectiveness of the ordinary methods
of treatment, and seasoning after treatment prevents the
rapid leaching out of the salts introduced to preserve the
timber.
3. The saving in freight where timber is shipped from one
place to another. Few persons realize how much water green
wood contains, or how much it will lose in a comparatively
short time. Experiments along this line with lodge-pole
pine, white oak, and chestnut gave results which were a
surprise to the companies owning the timber.
Freight charges vary considerably in different parts of the country;
but a decrease of 35 to 40 per cent in weight is important enough to
deserve everywhere serious consideration from those in charge of
timber operations.
When timber is shipped long distances over several roads, as is coming
to be more and more the case, the saving in freight will make a
material difference in the cost of lumber operations, irrespective of
any other advantages of seasoning.
Prevention of Checking and Splitting
Under present methods much timber is rendered unfit for use by
improper seasoning. Green timber, particularly when cut during
January, February, and March, when the roots are most active, contains
a large amount of water. When exposed to the sun and wind or to high
temperatures in a drying room, the water will evaporate more rapidly
from the outer than from the inner parts of the piece, and more
rapidly from the ends than from the sides. As the water evaporates,
the wood shrinks, and when the shrinkage is not fairly uniform the
wood cracks and splits.
When wet wood is piled in the sun, evaporation goes on with such
unevenness that the timbers split and crack in some cases so badly as
to become useless for the purpose for which it was intended. Such
uneven drying can be prevented by careful piling, keeping the logs
immersed in a log pond until wanted, or by piling or storing under an
open shed so that the sun cannot get at them.
Experiments have also demonstrated that injury to stock in the way of
checking and splitting always develops immediately after the stock is
taken into the dry kiln, and is due to the degree of humidity being
too low.
The receiving end of the kiln should always be kept moist, where the
stock has not been steamed before being put into the kiln, as when the
air is too dry it tends to dry the outside of the stock first--which
is termed "case-hardening"--and in so doing shrinks and closes up the
pores. As the material is moved down the kiln (as in the case of
"progressive kilns"), it absorbs a continually increasing amount of
heat, which tends to drive off the moisture still present in the
center of the piece, the pores on the outside having been closed up,
there is no exit for the vapor or steam that is being rapidly formed
in the center of the piece. It must find its way out in some manner,
and in doing so sets up strains, which result either in checking or
splitting. If the humidity had been kept higher, the outside of the
piece would not have dried so quickly, and the pores would have
remained open for the exit of the moisture from the interior of the
piece, and this trouble would have been avoided. (See also article
following.)
Shrinkage of Wood
Since in all our woods, cells with thick walls and cells with thin
walls are more or less intermixed, and especially as the spring-wood
and summer-wood nearly always differ from each other in this respect,
strains and tendencies to warp are always active when wood dries out,
because the summer-wood shrinks more than the spring-wood, and heavier
wood in general shrinks more than light wood of the same kind.
If a thin piece of wood after drying is placed upon a moist surface,
the cells on the under side of the piece take up moisture and swell
before the upper cells receive any moisture. This causes the under
side of the piece to become longer than the upper side, and as a
consequence warping occurs. Soon, however, the moisture penetrates to
all the cells and the piece straightens out. But while a thin board of
pine curves laterally it remains quite straight lengthwise, since in
this direction both shrinkage and swelling are small. If one side of a
green board is exposed to the sun, warping is produced by the removal
of water and consequent shrinkage of the side exposed; this may be
eliminated by the frequent turning of the topmost pieces of the piles
in order that they may be dried evenly.
As already stated, wood loses water faster from the ends than from the
longitudinal faces. Hence the ends shrink at a different rate from the
interior parts. The faster the drying at the surface, the greater is
the difference in the moisture of the different parts, and hence the
greater the strains and consequently also the greater amount of
checking. This becomes very evident when freshly cut wood is placed in
the sun, and still more when put into a hot, dry kiln. While most of
these smaller checks are only temporary, closing up again, some large
radial checks remain and even grow larger as drying progresses. Their
cause is a different one and will presently be explained. The
temporary checks not only appear at the ends, but are developed on
the sides also, only to a much smaller degree. They become especially
annoying on the surface of thick planks of hardwoods, and also on
peeled logs when exposed to the sun.
So far we have considered the wood as if made up only of parallel
fibres all placed longitudinally in the log. This, however, is not the
case. A large part of the wood is formed by the medullary or pith
rays. In pine over 15,000 of these occur on a square inch of a
tangential section, and even in oak the very large rays, which are
readily visible to the eye, represent scarcely a hundredth part of the
number which a microscope reveals, as the cells of these rays have
their length at right angles to the direction of the wood fibres.
If a large pith ray of white oak is whittled out and allowed to dry,
it is found to shrink greatly in its width, while, as we have stated,
the fibres to which the ray is firmly grown in the wood do not shrink
in the same direction. Therefore, in the wood, as the cells of the
pith ray dry they pull on the longitudinal fibres and try to shorten
them, and, being opposed by the rigidity of the fibres, the pith ray
is greatly strained. But this is not the only strain it has to bear.
Since the fibres shrink as much again as the pith ray, in this its
longitudinal direction, the fibres tend to shorten the ray, and the
latter in opposing this prevents the former from shrinking as much as
they otherwise would.
Thus the structure is subjected to two severe strains at right angles
to each other, and herein lies the greatest difficulty of wood
seasoning, for whenever the wood dries rapidly these fibres have not
the chance to "give" or accommodate themselves, and hence fibres and
pith rays separate and checking results, which, whether visible or
not, are detrimental in the use of the wood.
The contraction of the pith rays parallel to the length of the board
is probably one of the causes of the small amount of longitudinal
shrinkage which has been observed in boards. This smaller shrinkage of
the pith rays along the radius of the log (the length of the pith
ray), opposing the shrinkage of the fibres in this direction, becomes
one of the causes of the second great trouble in wood seasoning,
namely, the difference in the shrinkage along the radius and that
along the rings or tangent. This greater tangential shrinkage appears
to be due in part to the causes just mentioned, but also to the fact
that the greatly shrinking bands of summer-wood are interrupted along
the radius by as many bands of porous spring-wood, while they are
continuous in the tangential direction. In this direction, therefore,
each such band tends to shrink, as if the entire piece were composed
of summer-wood, and since the summer-wood represents the greater part
of the wood substance, this greater tendency to tangential shrinkage
prevails.
The effect of this greater tangential shrinkage effects every phase of
woodworking. It leads to permanent checks and causes the log or piece
to split open on drying. Sawed in two, the flat sides of the log
become convex; sawed into timber, it checks along the median line of
the four faces, and if converted into boards, the latter checks
considerably from the end through the center, all owing to the greater
tangential shrinkage of the wood.
Briefly, then, shrinkage of wood is due to the fact that the cell
walls grow thinner on drying. The thicker cell walls and therefore the
heavier wood shrinks most, while the water in the cell cavities does
not influence the volume of the wood.
Owing to the great difference of cells in shape, size, and thickness
of walls, and still more in their arrangement, shrinkage is not
uniform in any kind of wood. This irregularity produces strains, which
grow with the difference between adjoining cells and are greatest at
the pith rays. These strains cause warping and checking, but exist
even where no outward signs are visible. They are greater if the wood
is dried rapidly than if dried slowly, but can never be entirely
avoided.
Temporary checks are caused by the more rapid drying of the outer
parts of any stick; permanent checks are due to the greater shrinkage,
tangentially, along the rings than along the radius. This, too, is the
cause of most of the ordinary phenomena of shrinkage, such as the
difference in behavior of the entire and quartered logs, "bastard"
(tangent) and rift (radial) boards, etc., and explains many of the
phenomena erroneously attributed to the influence of bark, or of the
greater shrinkage of outer and inner parts of any log.
Once dry, wood may be swelled again to its original size by soaking in
water, boiling, or steaming. Soaked pieces on drying shrink again as
before; boiled and steamed pieces do the same, but to a slightly less
degree. Neither hygroscopicity, _i.e._, the capacity of taking up
water, nor shrinkage of wood can be overcome by drying at temperatures
below 200 degrees Fahrenheit. Higher temperatures, however, reduce
these qualities, but nothing short of a coaling heat robs wood of the
capacity to shrink and swell.
Rapidly dried in a kiln, the wood of oak and other hardwoods
"case-harden," that is, the outer part dries and shrinks before the
interior has a chance to do the same, and thus forms a firm shell or
case of shrunken, commonly checked wood around the interior. This
shell does not prevent the interior from drying, but when this drying
occurs the interior is commonly checked along the medullary rays,
commonly called "honeycombing" or "hollow-horning." In practice this
occurrence can be prevented by steaming or sweating the wood in the
kiln, and still better by drying the wood in the open air or in a shed
before placing in the kiln. Since only the first shrinkage is apt to
check the wood, any kind of lumber which has once been air-dried
(three to six months for one-inch stuff) may be subjected to kiln heat
without any danger from this source.
Kept in a bent or warped condition during the first shrinkage, the
wood retains the shape to which it has been bent and firmly opposes
any attempt at subsequent straightening.
Sapwood, as a rule, shrinks more than heartwood of the same weight,
but very heavy heartwood may shrink more than lighter sapwood. The
amount of water in wood is no criterion of its shrinkage, since in wet
wood most of the water is held in the cavities, where it has no effect
on the volume.
The wood of pine, spruce, cypress, etc., with its very regular
structure, dries and shrinks evenly, and suffers much less in
seasoning than the wood of broad-leaved (hardwood) trees. Among the
latter, oak is the most difficult to dry without injury.
Desiccating the air with certain chemicals will cause the wood to dry,
but wood thus dried at 80 degrees Fahrenheit will still lose water in
the kiln. Wood dried at 120 degrees Fahrenheit loses water still if
dried at 200 degrees Fahrenheit, and this again will lose more water
if the temperature be raised, so that _absolutely dry wood_ cannot be
obtained, and chemical destruction sets in before all the water is
driven off.
On removal from the kiln, the dry wood at once takes up moisture from
the air, even in the driest weather. At first the absorption is quite
rapid; at the end of a week a short piece of pine, 1-1/2 inches thick,
has regained two thirds of, and, in a few months, all the moisture
which it had when air-dry, 8 to 10 per cent, and also its former
dimensions. In thin boards all parts soon attain the same degree of
dryness. In heavy timbers the interior remains more moist for many
months, and even years, than the exterior parts. Finally an
equilibrium is reached, and then only the outer parts change with the
weather.
With kiln-dried woods all parts are equally dry, and when exposed, the
moisture coming from the air must pass through the outer parts, and
thus the order is reversed. Ordinary timber requires months before it
is at its best. Kiln-dried timber, if properly handled, is prime at
once.
Dry wood if soaked in water soon regains its original volume, and in
the heartwood portion it may even surpass it; that is to say, swell to
a larger dimension than it had when green. With the soaking it
continues to increase in weight, the cell cavities filling with water,
and if left many months all pieces sink. Yet after a year's immersion
a piece of oak 2 by 2 inches and only 6 inches long still contains
air; _i.e._, it has not taken up all the water it can. By rafting or
prolonged immersion, wood loses some of its weight, soluble materials
being leached out, but it is not impaired either as fuel or as
building material. Immersion, and still more boiling and steaming,
reduce the hygroscopicity of wood and therefore also the troublesome
"working," or shrinking and swelling.
Exposure in dry air to a temperature of 300 degrees Fahrenheit for a
short time reduces but does not destroy the hygroscopicity, and with
it the tendency to shrink and swell. A piece of red oak which has been
subjected to a temperature of over 300 degrees Fahrenheit still swells
in hot water and shrinks in a dry kiln.
Expansion of Wood
It must not be forgotten that timber, in common with every other
material, expands as well as contracts. If we extract the moisture
from a piece of wood and so cause it to shrink, it may be swelled to
its original volume by soaking it in water, but owing to the
protection given to most timber in dwelling-houses it is not much
affected by wet or damp weather. The shrinkage is more apparent, more
lasting, and of more consequence to the architect, builder, or owner
than the slight expansion which takes place, as, although the amount
of moisture contained in wood varies with the climate conditions, the
consequence of dampness or moisture on good timber used in houses only
makes itself apparent by the occasional jamming of a door or window in
wet or damp weather.
Considerable expansion, however, takes place in the wood-paving of
streets, and when this form of paving was in its infancy much trouble
occurred owing to all allowances not having been made for this
contingency, the trouble being doubtless increased owing to the blocks
not being properly seasoned; curbing was lifted or pushed out of line
and gully grids were broken by this action. As a rule in street paving
a space of one or two inches wide is now left next to the curb, which
is filled with sand or some soft material, so that the blocks may
expand longitudinally without injuring the contour or affecting the
curbs. But even with this arrangement it is not at all unusual for an
inch or more to have to be cut off paving blocks parallel to the
channels some time after the paving has been laid, owing to the
expansion of the wood exceeding the amounts allowed.
Considerable variation occurs in the expansion of wood blocks, and it
is noticeable in the hardwoods as well as in the softwoods, and is
often greater in the former than in the latter.
Expansion takes place in the direction of the length of the blocks as
they are laid across the street, and causes no trouble in the other
direction, the reason being that the lengthway of a block of wood is
across the grain, of the timber, and it expands or contracts as a
plank does. On one occasion, in a roadway forty feet wide, expansion
occurred until it amounted to four inches on each side, or eight
inches in all. This continual expansion and contraction is doubtless
the cause of a considerable amount of wood street-paving bulging and
becoming filled with ridges and depressions.
Elimination of Stain and Mildew
A great many manufacturers, and particularly those located in the
Southern States, experience a great amount of difficulty in their
timber becoming stained and mildewed. This is particularly true with
gum wood, as it will frequently stain and mould in twenty-four hours,
and they have experienced so much of this trouble that they have, in a
great many instances, discontinued cutting it during the summer
season.
If this matter were given proper attention they should be able to
eliminate a great deal of this difficulty, as no doubt they will find
after investigation that the mould has been caused by the stock being
improperly piled to the weather.
Freshly sawn wood, placed in close piles during warm, damp weather in
the months of July and August, presents especially favorable
conditions for mould and stain. In all cases it is the moist condition
and retarded drying of the wood which causes this. Therefore, any
method which will provide for the rapid drying of the wood before or
after piling will tend to prevent the difficulty, and the best method
for eliminating mould is (1) to provide for as little delay as
possible between the felling of the tree, and its manufacture into
rough products before the sap has had an opportunity of becoming sour.
This is especially necessary with trees felled from April to
September, in the region north of the Gulf States, and from March to
November in the latter, while the late fall and winter cutting should
all be worked up by March or April. (2) The material should be piled
to the weather immediately after being sawn or cut, and every
precaution should be taken in piling to facilitate rapid drying, by
keeping the piles or ricks up off the ground. (3) All weeds (and
emphasis should be placed on the ALL) and other vegetation should be
kept well clear of the piles, in order that the air may have a clear
and unobstructed passage through and around the piles, and (4) the
piles should be so constructed that each stick or piece will have as
much air space about it as it is possible to give to it.
If the above instructions are properly carried out, there will be
little or no difficulty experienced with mould appearing on the
lumber.
SECTION IX
DIFFICULTIES OF DRYING WOOD
Seasoning and kiln-drying is so important a process in the manufacture
of woods that a need is keenly felt for fuller information regarding
it, based upon scientific study of the behavior of various species at
different mechanical temperatures and under different mechanical
drying processes. The special precautions necessary to prevent loss of
strength or distortion of shape render the drying of wood especially
difficult.
All wood when undergoing a seasoning process, either natural (by air)
or mechanical (by steam or heat in a dry kiln), checks or splits more
or less. This is due to the uneven drying-out of the wood and the
consequent strains exerted in opposite directions by the wood fibres
in shrinking. This shrinkage, it has been proven, takes place both
end-wise and across the grain of the wood. The old tradition that wood
does not shrink end-wise has long since been shattered, and it has
long been demonstrated that there is an end-wise shrinkage.
In some woods it is very light, while in others it is easily
perceptible. It is claimed that the average end shrinkage, taking all
the woods, is only about 1-1/2 per cent. This, however, probably has
relation to the average shrinkage on ordinary lumber as it is used and
cut and dried. Now if we depart from this and take veneer, or basket
stock, or even stave bolts where they are boiled, causing swelling
both end-wise and across the grain or in dimension, after they are
thoroughly dried, there is considerably more evidence of end
shrinkage. In other words, a slack barrel stave of elm, say, 28 or 30
inches in length, after being boiled might shrink as much in
thoroughly drying-out as compared to its length when freshly cut, as a
12-foot elm board.
It is in cutting veneer that this end shrinkage becomes most readily
apparent. In trimming with scoring knives it is done to exact measure,
and where stock is cut to fit some specific place there has been
observed a shrinkage on some of the softer woods, like cottonwood,
amounting to fully 1/8 of an inch in 36 inches. And at times where
drying has been thorough the writer has noted a shrinkage of 1/8 of an
inch on an ordinary elm cabbage-crate strip 36 inches long, sawed from
the log without boiling.
There are really no fixed rules of measurement or allowance, however,
because the same piece of wood may vary under different conditions,
and, again, the grain may cross a little or wind around the tree, and
this of itself has a decided effect on the amount of what is termed
"end shrinkage."
There is more checking in the wood of the broad-leaf (hardwood) trees
than in that of the coniferous (softwood) trees, more in sapwood than
in heartwood, and more in summer-wood than in spring-wood.
Inasmuch as under normal conditions of weather, water evaporates less
rapidly during the early seasoning of winter, wood that is cut in the
autumn and early winter is considered less subject to checking than
that which is cut in spring and summer.
Rapid seasoning, except after wood has been thoroughly soaked or
steamed, almost invariably results in more or less serious checking.
All hardwoods which check or warp badly during the seasoning should be
reduced to the smallest practicable size before drying to avoid the
injuries involved in this process, and wood once seasoned _should
never again be exposed to the weather_, since all injuries due to
seasoning are thereby aggravated.
Seasoning increases the strength of wood in every respect, and it is
therefore of great importance to protect the wood against moisture.
Changes rendering Drying difficult
An important property rendering drying of wood peculiarly difficult is
the changes which occur in the hygroscopic properties of the surface
of a stick, and the rate at which it will allow moisture to pass
through it. If wood is dried rapidly the surface soon reaches a
condition where the transfusion is greatly hindered and sometimes
appears almost to cease. The nature of this action is not well
understood and it differs greatly in different species. Bald cypress
(_Taxodium distichum_) is an example in which this property is
particularly troublesome. The difficulty can be overcome by regulating
the humidity during the drying operation. It is one of the factors
entering into production of what is called "case-hardening" of wood,
where the surface of the piece becomes hardened in a stretched or
expanded condition, and subsequent shrinkage of the interior causes
"honeycombing," "hollow-horning," or internal checking. The outer
surface of the wood appears to undergo a chemical change in the nature
of hydrolization or oxidization, which alters the rate of absorption
and evaporation in the air.
As the total amount of shrinkage varies with the rate at which the
wood is dried, it follows that the outer surface of a rapidly dried
board shrinks less than the interior. This sets up an internal stress,
which, if the board be afterward resawed into two thinner boards by
slicing it through the middle, causes the two halves to cup with their
convex surfaces outward. This effect may occur even though the
moisture distribution in the board has reached a uniform condition,
and the board is thoroughly dry before it is resawed. It is distinct
from the well-known "case-hardening" effect spoken of above, which is
caused by unequal moisture conditions.
The manner in which the water passes from the interior of a piece of
wood to its surface has not as yet been fully determined, although it
is one of the most important factors which influence drying. This must
involve a transfusion of moisture through the cell walls, since, as
already mentioned, except for the open vessels in the hardwoods, free
resin ducts in the softwoods, and possibly the intercellular spaces,
the cells of green wood are enclosed by membranes and the water must
pass through the walls or the membranes of the pits. Heat appears to
increase this transfusion, but experimental data are lacking.
It is evident that to dry wood properly a great many factors must be
taken into consideration aside from the mere evaporation of moisture.
Losses Due to Improper Kiln-drying
In some cases there is practically no loss in drying, but more often
it ranges from 1 to 3 per cent, and 7 to 10 per cent in refractory
woods such as gum. In exceptional instances the losses are as high as
33 per cent.
In air-drying there is little or no control over the process; it may
take place too rapidly on some days and too slowly on others, and it
may be very non-uniform.
Hardwoods in large sizes almost invariably check.
By proper kiln-drying these unfavorable circumstances may be
eliminated. However, air-drying is unquestionably to be preferred to
bad kiln-drying, and when there is any doubt in the case it is
generally safer to trust to air-drying.
If the fundamental principles are all taken care of, green lumber can
be better dried in the dry kiln.
Properties of Wood that affect Drying
It is clear, from the previous discussion of the structure of wood,
that this property is of first importance among those influencing the
seasoning of wood. The free water way usually be extracted quite
readily from porous hardwoods. The presence of tyloses in white oak
makes even this a difficult problem. On the other hand, its more
complex structure usually renders the hygroscopic moisture quite
difficult to extract.
The lack of an open, porous structure renders the transfusion of
moisture through some woods very slow, while the reverse may be true
of other species. The point of interest is that all the different
variations in structure affect the drying rates of woods. The
structure of the gums suggests relatively easy seasoning.
Shrinkage is a very important factor affecting the drying of woods.
Generally speaking, the greater the shrinkage the more difficult it is
to dry wood. Wood shrinks about twice as much tangentially as
radially, thus introducing very serious stresses which may cause loss
in woods whose total shrinkage is large. It has been found that the
amount of shrinkage depends, to some extent, on the rate and
temperature at which woods season. Rapid drying at high or low
temperature results in slight shrinkage, while slow drying, especially
at high temperature, increases the shrinkage.
As some woods must be dried in one way and others in other ways, to
obtain the best general results, this effect may be for the best in
one case and the reverse in others. As an example one might cite the
case of Southern white oak. This species must be dried very slowly at
low temperatures in order to avoid the many evils to which it is heir.
It is interesting to note that this method tends to increase the
shrinkage, so that one might logically expect such treatment merely to
aggravate the evils. Such is not the case, however, as too fast drying
results in other defects much worse than that of excessive shrinkage.
Thus we see that the shrinkage of any given species of wood depends to
a great extent on the method of drying. Just how much the shrinkage of
gum is affected by the temperature and drying rate is not known at
present. There is no doubt that the method of seasoning affects the
shrinkage of the gums, however. It is just possible that these woods
may shrink longitudinally more than is normal, thus furnishing another
cause for their peculiar action under certain circumstances. It has
been found that the properties of wood which affect the seasoning of
the gums are, in the order of their importance: (1) The indeterminate
and erratic grain; (2) the uneven shrinkage with the resultant
opposing stresses; (3) the plasticity under high temperature while
moist; and (4) the slight apparent lack of cohesion between the
fibres. The first, second, and fourth properties are clearly
detrimental, while the third may possibly be an advantage in reducing
checking and "case-hardening."
The grain of the wood is a prominent factor also affecting the
problem. It is this factor, coupled with uneven shrinkage, which is
probably responsible, to a large extent, for the action of the gums in
drying. The grain may be said to be more or less indeterminate. It is
usually spiral, and the spiral may reverse from year to year of the
tree's growth. When a board in which this condition exists begins to
shrink, the result is the development of opposing stresses, the effect
of which is sometimes disastrous. The shrinkage around the knots seems
to be particularly uneven, so that checking at the knots is quite
common.
Some woods, such as Western red cedar, redwood, and eucalyptus, become
very plastic when hot and moist. The result of drying-out the free
water at high temperature may be to collapse the cells. The gums are
known to be quite soft and plastic, if they are moist, at high
temperature, but they do not collapse so far as we have been able to
determine.
The cells of certain species of wood appear to lack cohesion,
especially at the junction between the annual rings. As a result,
checks and ring shakes are very common in Western larch and hemlock.
The parenchyma cells of the medullary rays in oak do not cohere
strongly and often check open, especially when steamed too severely.
Unsolved Problems in Kiln-drying
1. Physical data of the properties of wood in relation to
heat are meagre.
2. Figures on the specific heat of wood are not readily
available, though upon this rests not only the exact
operation of heating coils for kilns, but the theory of
kiln-drying as a whole.
3. Great divergence is shown in the results of experiments
in the conductivity of wood. It remains to be seen whether
the known variation of conductivity with moisture content
will reduce these results to uniformity.
4. The maximum or highest temperature to which the different
species of wood may be exposed without serious loss of
strength has not yet been determined.
5. The optimum or absolute correct temperature for drying
the different species of wood is as yet entirely unsettled.
6. The inter-relation between wood and water is as
imperfectly known to dry-kiln operators as that between wood
and heat.
7. What moisture conditions obtain in a stick of air-dried
wood?
8. How is the moisture distinguished?
9. What is its form?
10. What is the meaning of the peculiar surface conditions
which even in air-dried wood appear to indicate incipient
"case-hardening"?
11. The manner in which the water passes from the interior
of a piece of wood to its surface has not as yet been fully
determined.
These questions can be answered thus far only by speculation or, at
best, on the basis of incomplete data.
Until these problems are solved, kiln-drying must necessarily remain
without the guidance of complete scientific theory.
A correct understanding of the principles of drying is rare, and
opinions in regard to the subject are very diverse. The same lack of
knowledge exists in regard to dry kilns. The physical properties of
the wood which complicate the drying operation and render it distinct
from that of merely evaporating free water from some substance like a
piece of cloth must be studied experimentally. It cannot well be
worked out theoretically.
SECTION X
HOW WOOD IS SEASONED
Methods of Drying
The choice of a method of drying depends largely upon the object in
view. The principal objects may be grouped under three main heads, as
follows:
1. To reduce shipping weight.
2. To reduce the quantity necessary to carry in stock.
3. To prepare the wood for its ultimate use and improve its
qualities.
When wood will stand the temperature without excessive checking or
undue shrinkage or loss in strength, the first object is most readily
attained by heating the wood above the boiling point in a closed
chamber, with a large circulation of air or vapor, so arranged that
the excess steam produced will escape. This process manifestly does
not apply to many of the hardwoods, but is applicable to many of the
softwoods. It is used especially in the northwestern part of the
United States, where Douglas fir boards one inch thick are dried in
from 40 to 65 hours, and sometimes in as short a time as 24 hours. In
the latter case superheated steam at 300 degrees Fahrenheit was forced
into the chamber but, of course, the lumber could not be heated
thereby much above the boiling point so long as it contained any free
water.
This lumber, however, contained but 34 per cent moisture to start
with, and the most rapid rate was 1.6 per cent loss per hour.
The heat of evaporation may be supplied either by superheated steam or
by steam pipes within the kiln itself.
The quantity of wood it is necessary to carry in stock is naturally
reduced when either of the other two objects is attained and,
therefore, need not necessarily be discussed.
In drying to prepare for use and to improve quality, careful and
scientific drying is called for. This applies more particularly to the
hardwoods, although it may be required for softwoods also.
Drying at Atmospheric Pressure
Present practice of kiln-drying varies tremendously and there is no
uniformity or standard method.
Temperatures vary anywhere from 65 to 165 degrees Fahrenheit, or even
higher, and inch boards three to six months on the sticks are being
dried in from four days to three weeks, and three-inch material in
from two to five months.
All methods in use at atmospheric pressure may be classified under the
following headings. The kilns may be either progressive or
compartment, and preliminary steaming may or may not be used with any
one of these methods:
1. Dry air heated. This is generally obsolete.
2. Moist air.
_a._ Ventilated.
_b._ Forced draft.
_c._ Condensing.
_d._ Humidity regulated.
_e._ Boiling.
3. Superheated steam.
Drying under Pressure and Vacuum
Various methods of drying wood under pressures other than atmospheric
have been tried. Only a brief mention of this subject will be made.
Where the apparatus is available probably the quickest way to dry wood
is first to heat it in saturated steam at as high a temperature as the
species can endure without serious chemical change until the heat has
penetrated to the center, then follow this with a vacuum.
By this means the self-contained specific heat of the wood and the
water is made available for the evaporation, and the drying takes
place from the inside outwardly, just the reverse of that which occurs
by drying by means of external heat.
When the specimen has cooled this process is then to be repeated until
it has dried down to fibre-saturation point. It cannot be dried much
below this point by this method, since the absorption during the
heating operation will then equal the evaporation during the cooling.
It may be carried further, however, by heating in partially humidified
air, proportioning the relative humidity each time it is heated to the
degree of moisture present in the wood.
The point to be considered in this operation is that during the
heating process no evaporation shall be allowed to take place, but
only during the cooling. In this way surface drying and
"case-hardening" are prevented since the heat is from within and the
moisture passes from the inside outwardly. However, with some species,
notably oak, surface cracks appear as a network of fine checks along
the medullary rays.
In the first place, it should be borne in mind that it is the heat
which produces evaporation and not the air nor any mysterious property
assigned to a "vacuum."
For every pound of water evaporated at ordinary temperatures
approximately 1,000 British thermal units of heat are used up, or
"become latent," as it is called. This is true whether the evaporation
takes place in a vacuum or under a moderate air pressure. If this heat
is not supplied from an outside source it must be supplied by the
water itself (or the material being dried), the temperature of which
will consequently fall until the surrounding space becomes saturated
with vapor at a pressure corresponding to the temperature which the
water has reached; evaporation will then cease. The pressure of the
vapor in a space saturated with water vapor increases rapidly with
increase of temperature. At a so-called vacuum of 28 inches, which is
about the limit in commercial operations, and in reality signifies an
actual pressure of 2 inches of mercury column, the space will be
saturated with vapor at 101 degrees Fahrenheit. Consequently, no
evaporation will take place in such a vacuum unless the water be
warmer than 101 degrees Fahrenheit, provided there is no air leakage.
The qualification in regard to air is necessary, for the sake of
exactness, for the following reason: In any given space the total
actual pressure is made up of the combined pressures of all the gases
present. If the total pressure ("vacuum") is 2 inches, and there is no
air present, it is all produced by the water vapor (which saturates
the space at 101 degrees Fahrenheit); but if some air is present and
the total pressure is still maintained at 2 inches, then there must be
less vapor present, since the air is producing part of the pressure
and the space is no longer saturated at the given temperature.
Consequently further evaporation may occur, with a corresponding
lowering of the temperature of the water, until a balance is again
reached. Without further explanation it is easy to see that but little
water can be evaporated by a vacuum alone without addition of heat,
and that the prevalent idea that a vacuum can of itself produce
evaporation is a fallacy. If heat be supplied to the water, however,
either by conduction or radiation, evaporation will take place in
direct proportion to the amount of heat supplied, so long as the
pressure is kept down by the vacuum pump.
At 30 inches of mercury pressure (one atmosphere) the space becomes
saturated with vapor and equilibrium is established at 212 degrees
Fahrenheit. If heat be now supplied to the water, however, evaporation
will take place in proportion to the amount of heat supplied, so long
as the pressure remains that of one atmosphere, just as in the case of
the vacuum. Evaporation in this condition, where the vapor pressure at
the temperature of the water is equal to the gas pressure on the
water, is commonly called "boiling," and the saturated vapor entirely
displaces the air under continuous operation. Whenever the space is
not saturated with vapor, whether air is present or not, evaporation
will take place, by boiling if no air be present or by diffusion under
the presence of air, until an equilibrium between temperature and
vapor pressure is resumed.
Relative humidity is simply the ratio of the actual vapor pressure
present in a given space to the vapor pressure when the space is
saturated with vapor at the given temperature. It matters not whether
air be present or not. One hundred per cent humidity means that the
space contains all the vapor which it can hold at the given
temperature--it is saturated. Thus at 100 per cent humidity and 212
degrees Fahrenheit the space is saturated, and since the pressure of
saturated vapor at this temperature is one atmosphere, no air can be
present under these conditions. If, however, the total pressure at
this temperature were 20 pounds (5 pounds gauge), then it would mean
that there was 5 pounds air pressure present in addition to the vapor,
yet the space would still be saturated at the given temperature.
Again, if the temperature were 101 degrees Fahrenheit, the pressure of
saturated vapor would be only 1 pound, and the additional pressure of
14 pounds, if the total pressure were atmospheric, would be made up of
air. In order to have no air present and the space still saturated at
101 degrees Fahrenheit, the total pressure must be reduced to 1 pound
by a vacuum pump. Fifty per cent relative humidity, therefore,
signifies that only half the amount of vapor required to saturate the
space at the given temperature is present. Thus at 212 degrees
Fahrenheit temperature the vapor pressure would only be 7-1/2 pounds
(vacuum of 15 inches gauge). If the total pressure were atmospheric,
then the additional 7-1/2 pounds would be simply air.
"Live steam" is simply water-saturated vapor at a pressure usually
above atmospheric. We may just as truly have live steam at pressures
less than atmospheric, at a vacuum of 28 inches for instance. Only in
the latter case its temperature would be lower, _viz._, 101 degrees
Fahrenheit.
Superheated steam is nothing more than water vapor at a relative
humidity less than saturation, but is usually considered at pressures
above atmospheric, and in the absence of air. The atmosphere at, say,
50 per cent relative humidity really contains superheated steam or
vapor, the only difference being that it is at a lower temperature and
pressure than we are accustomed to think of in speaking of superheated
steam, and it has air mixed with it to make up the deficiency in
pressure below the atmosphere.
Two things should now be clear; that evaporation is produced by heat
and that the presence or absence of air does not influence the amount
of evaporation. It does, however, influence the rate of evaporation,
which is retarded by the presence of air. The main things influencing
evaporation are, first, the quantity of heat supplied and, second, the
relative humidity of the immediately surrounding space.
Drying by Superheated Steam
What this term really signifies is simply water vapor in the absence
of air in a condition of less than saturation. Kilns of this type are,
properly speaking, vapor kilns, and usually operate at atmospheric
pressure, but may be used at greater pressures or at less pressures.
As stated before, the vapor present in the air at any humidity less
than saturation is really "superheated steam," only at a lower
pressure than is ordinarily understood by this term, and mixed with
air. The main argument in favor of this process seems to be based on
the idea that steam is moist heat. This is true, however, only when
the steam is near saturation. When it is superheated it is just as dry
as air containing the same relative humidity. For instance, steam at
atmospheric pressure and heated to 248 degrees Fahrenheit has a
relative humidity of only 50 per cent and is just as dry as air
containing the same humidity. If heated to 306 degrees Fahrenheit, its
relative humidity is reduced to 20 per cent; that is to say, the ratio
of its actual vapor pressure (one atmosphere) to the pressure of
saturated vapor at this temperature (five atmospheres) is 1:5, or 20
per cent. Superheated vapor in the absence of air, however, parts with
its heat with great rapidity and finally becomes saturated when it has
lost all of its ability to cause evaporation. In this respect it is
more moist than air when it comes in contact with bodies which are at
a lower temperature. When saturated steam is used to heat the lumber
it can raise the temperature of the latter to its own temperature, but
cannot produce evaporation unless, indeed, the pressure is varied.
Only by the heat supplied above the temperature of saturation can
evaporation be produced.
Impregnation Methods
Methods of partially overcoming the shrinkage by impregnation of the
cell walls with organic materials closely allied to the wood substance
itself are in use. In one of these which has been patented, sugar is
used as the impregnating material, which is subsequently hardened or
"caramelized" by heating. Experiments which the United States Forest
Service has made substantiate the claims that the sugar does greatly
reduce the shrinkage of the wood; but the use of impregnation
processes is determined rather from a financial economic standpoint
than by the physical result obtained.
Another process consists in passing a current of electricity through
the wet boards or through the green logs before sawing. It is said
that the ligno cellulose and the sap are thus transformed by
electrolysis, and that the wood subsequently dries more rapidly.
Preliminary Treatments
In many dry kiln operations, especially where the kilns are not
designed for treatments with very moist air, the wood is allowed to
air-season from several months to a year or more before running it
into the dry kiln. In this way the surface dries below its
fibre-saturation point and becomes hardened or "set" and the
subsequent shrinkage is not so great. Moreover, there is less danger
of surface checking in the kiln, since the surface has already passed
the danger point. Many woods, however, check severely in air-drying or
case-harden in the air. It is thought that such woods can be
satisfactorily handled in a humidity-regulated kiln direct from the
saw.
Preliminary steaming is frequently used to moisten the surface if
case-hardened, and to heat the lumber through to the center before
drying begins. This is sometimes done in a separate chamber, but more
often in a compartment of the kiln itself, partitioned off by means of
a curtain which can be raised or lowered as circumstances require.
This steaming is usually conducted at atmospheric pressure and
frequently condensed steam is used at temperatures far below 212
degrees Fahrenheit. In a humidity-regulated kiln this preliminary
treatment may be omitted, since nearly saturated conditions can be
maintained and graduated as the drying progresses.
Recently the process of steaming at pressures up to 20 pounds gauge in
a cylinder for short periods of time, varying from 5 to 20 minutes, is
being advocated in the United States. The truck load is run into the
cylinder, steamed, and then taken directly out into the air. It may
subsequently be placed in the dry kiln if further drying is desired.
The self-contained heat of the wood evaporates considerable moisture,
and the sudden drying of the boards causes the shrinkage to be reduced
slightly in some cases. Such short periods of steaming under 20 pounds
pressure do not appear to injure the wood mechanically, although they
do darken the color appreciably, especially of the sapwood of the
species having a light-colored sap, as black walnut (_Juglans nigra_)
and red gum (_Liquidamber styraciflua_). Longer periods of steaming
have been found to weaken the wood. There is a great difference in the
effect on different species, however.
Soaking wood for a long time before drying has been practised, but
experiments indicate that no particularly beneficial results, from the
drying standpoint, are attained thereby. In fact, in some species
containing sugars and allied substances it is probably detrimental
from the shrinkage standpoint. If soaked in boiling water some species
shrink and warp more than if dried without this treatment.
In general, it may be said that, except possibly for short-period
steaming as described above, steaming and soaking hardwoods at
temperatures of 212 degrees Fahrenheit or over should be avoided if
possible.
It is the old saying that wood put into water shortly after it is
felled, and left in water for a year or more, will be perfectly
seasoned after a short subsequent exposure to the air. For this reason
rivermen maintain that timber is made better by rafting. Herzenstein
says: "Floating the timber down rivers helps to wash out the sap, and
hence must be considered as favorable to its preservation, the more so
as it enables it to absorb more preservative."
Wood which has been buried in swamps is eagerly sought after by
carpenters and joiners, because it has lost all tendency to warp and
twist. When first taken from the swamp the long-immersed logs are very
much heavier than water, but they dry with great rapidity. A cypress
log from the Mississippi Delta, which two men could barely handle at
the time it was taken out some years ago, has dried out so much since
then that to-day one man can lift it with ease. White cedar telegraph
poles are said to remain floating in the water of the Great Lakes
sometimes for several years before they are set in lines and to last
better than freshly cut poles.
It is very probable that immersion for long periods in water does
materially hasten subsequent seasoning. The tannins, resins,
albuminous materials, etc., which are deposited in the cell walls of
the fibres of green wood, and which prevent rapid evaporation of the
water, undergo changes when under water, probably due to the action of
bacteria which live without air, and in the course of time many of
these substances are leached out of the wood. The cells thereby become
more and more permeable to water, and when the wood is finally brought
into the air the water escapes very rapidly and very evenly.
Herzenstein's statement that wood prepared by immersion and subsequent
drying will absorb more preservative, and that with greater rapidity,
is certainly borne out by experience in the United States.
It is sometimes claimed that all seasoning preparatory to treatment
with a substance like tar oil might be done away with by putting the
green wood into a cylinder with the oil and heating to 225 degrees
Fahrenheit, thus driving the water off in the form of steam, after
which the tar oil would readily penetrate into the wood. This is the
basis of the so-called "Curtiss process" of timber treatment. Without
going into any discussion of this method of creosoting, it may be said
that the same objection made for steaming holds here. In order to get
a temperature of 212 degrees Fahrenheit in the center of the treated
wood, the outside temperature would have to be raised so high that the
strength of the wood might be seriously injured.
A company on the Pacific coast which treats red fir piling asserts
that it avoids this danger by leaving the green timber in the tar oil
at a temperature which never exceeds 225 degrees Fahrenheit for from
five to twelve hours, until there is no further evidence of water
vapor coming out of the wood. The tar oil is then run out, and a
vacuum is created for about an hour, after which the oil is run in
again and is kept in the cylinders under 100 pounds pressure for from
ten to twelve hours, until the required amount of absorption has been
reached (about 12 pounds per cubic foot).
Out-of-door Seasoning
The most effective seasoning is without doubt that obtained by the
uniform, slow drying which takes place in properly constructed piles
outdoors, under exposure to the winds and the sun. Lumber has always
been seasoned in this way, which is still the best for ordinary
purposes.
It is probable for the sake of economy, air-drying will be eliminated
in the drying process of the future without loss to the quality of the
product, but as yet no effective method has been discovered whereby
this may be accomplished, because nature performs certain functions in
air-drying that cannot be duplicated by artificial means. Because of
this, hardwoods, as a rule, cannot be successfully kiln-dried green or
direct from the saw, and must receive a certain amount of preliminary
air-drying before being placed in a dry kiln.
The present methods of air-seasoning in use have been determined by
long experience, and are probably as good as they could be made for
present conditions. But the same care has not up to this time been
given to the seasoning of such timber as ties, bridge material, posts,
telegraph and telephone poles, etc. These have sometimes been piled
more or less intelligently, but in the majority of cases their value
has been too low to make it seem worth while to pile with reference to
anything beyond convenience in handling.
In piling material for air-seasoning, one should utilize high, dry
ground when possible, and see that the foundations are high enough off
the ground, so that there is proper air circulation through the bottom
of the piles, and also that the piles are far enough apart so that the
air may circulate freely through and around them.
It is air circulation that is desired in all cases of drying, both in
dry kilns and out-of-doors, and not sunshine; that is, not the sun
shining directly upon the material. The ends also should be protected
from the sun, and everything possible done to induce a free
circulation of air, and to keep the foundations free from all plant
growth.
Naturally, the heavier the material to be dried, the more difficulty
is experienced from checking, which has its most active time in the
spring when the sap is rising. In fact the main period of danger in
material checking comes with the March winds and the April showers,
and not infrequently in the South it occurs earlier than that. In
other words, as soon as the sap begins to rise, the timber shows signs
of checking, and that is the time to take extra precautions by careful
piling and protection from the sun. When the hot days of summer arrive
the tendency to check is not so bad, but stock will sour from the
heat, stain from the sap, mildew from moisture, and fall a prey to
wood-destroying insects.
It has been proven in a general way that wood will season more slowly
in winter than in summer, and also that the water content during
various months varies. In the spring the drying-out of wood cut in
October and November will take place more rapidly.
SECTION XI
KILN-DRYING OF WOOD
Advantages of Kiln-drying over Air-drying
Some of the advantages of kiln-drying to be secured over air-drying in
addition to reducing the shipping weight and lessening quantity of
stock are the following:
1. Less material lost.
2. Better quality of product.
3. Prevention of sap stain and mould.
4. Fixation of gums and resins.
5. Reduction of hygroscopicity.
This reduction in the tendency to take up moisture means a reduction
in the "working" of the material which, even though slight, is of
importance.
The problem of drying wood in the best manner divides itself into two
distinct parts, one of which is entirely concerned with the behavior
of the wood itself and the physical phenomena involved, while the
other part has to do with the control of the drying process.
Physical Conditions governing the Drying of Wood
1. Wood is soft and plastic while hot and moist, and becomes
"set" in whatever shape it dries. Some species are much more
plastic than others.
2. Wood substance begins to shrink only when it dries below
the fibre-saturation point, at which it contains from 25 to
30 per cent moisture based on its dry weight. Eucalyptus and
certain other species appear to be exceptions to this law.
3. The shrinkage of wood is about twice as great
circumferentially as in the radial direction; lengthwise, it
is very slight.
4. Wood shrinks most when subjected, while kept moist, to
slow drying at high temperatures.
5. Rapid drying produces less shrinkage than slow drying at
high temperatures, but is apt to cause case-hardening and
honeycombing, especially in dense woods.
6. Case-hardening, honeycombing, and cupping result directly
from conditions 1, 4, and 5, and chemical changes of the
outer surface.
7. Brittleness is caused by carrying the drying process too
far, or by using too high temperatures. Safe limits of
treatment vary greatly for different species.
8. Wood absorbs or loses moisture in proportion to the
relative humidity in the air, not according to the
temperature. This property is called its "hygroscopicity."
9. Hygroscopicity and "working" are reduced but not
eliminated by thorough drying.
10. Moisture tends to transfuse from the hot towards the
cold portion of the wood.
11. Collapse of the cells may occur in some species while
the wood is hot and plastic. This collapse is independent of
subsequent shrinkage.
Theory of Kiln-drying
The dry kiln has long since acquired particular appreciation at the
hands of those who have witnessed its time-saving qualities, when
practically applied to the drying of timber. The science of drying is
itself of the simplest, the exposure to the air being, indeed, the
only means needed where the matter of time is not called into
question. Otherwise, where hours, even minutes, have a marked
significance, then other means must be introduced to bring about the
desired effect. In any event, however, the same simple and natural
remedy pertains,--the absorption of moisture. This moisture in green
timber is known as "sap", which is itself composed of a number of
ingredients, most important among which are water, resin, and albumen.
All dry kilns in existence use heat to season timber; that is, to
drive out that portion of the "sap" which is volatile.
The heat does not drive out the resin of the pines nor the albumen of
the hardwoods. It is really of no advantage in this respect. Resin in
its hardened state as produced by heat is only slowly soluble in water
and contains a large proportion of carbon, the most stable form of
matter. Therefore, its retention in the pores of the wood is a
positive advantage.
To produce the ideal effect the drying must commence at the heart of
the piece and work outward, the moisture being removed from the
surface as fast as it exudes from the pores of the wood. To
successfully accomplish this, adjustments must be available to
regulate the temperature, circulation, and humidity according to the
variations of the atmospheric conditions, the kind and condition of
the material to be dried.
This ideal effect is only attained by the use of a type of dry kiln in
which the surface of the lumber is kept soft, the pores being left
open until all the moisture within has been volatilized by the heat
and carried off by a free circulation of air. When the moisture has
been removed from the pores, the surface is dried without closing the
pores, resulting in timber that is clean, soft, bright, straight, and
absolutely free from stains, checks, or other imperfections.
Now, no matter how the method of drying may be applied, it must be
remembered that vapor exists in the atmosphere at all times, its
volume being regulated by the capacity of the temperature absorbed. To
kiln-dry properly, a free current of air must be maintained, of
sufficient volume to carry off this moisture. Now, the capacity of
this air for drying depends entirely upon the ability of its
temperature to absorb or carry off a larger proportion of moisture
than that apportioned by natural means. Thus, it will be seen, a cubic
foot of air at 32 degrees Fahrenheit is capable of absorbing only two
grains of water, while at 160 degrees, it will dispose of ninety
grains. The air, therefore, should be made as dry as possible and
caused to move freely, so as to remove all moisture from the surface
of the wood as soon as it appears. Thus the heat effects a double
purpose, not only increasing the rate of evaporation, but also the
capacity of the air for absorption. Where these means are applied,
which rely on the heat alone to accomplish this purpose, only that of
the moisture which is volatile succumbs, while the albumen and resin
becoming hardened under the treatment close up the pores of the wood.
This latter result is oft-times accomplished while moisture yet
remains and which in an enforced effort to escape bursts open the
cells in which it has been confined and creates what is known as
"checks."
Therefore, taking the above facts into consideration, the essentials
for the successful kiln-drying of wood may be enumerated as follows:
1. The evaporation from the surface of a stick should not
exceed the rate at which the moisture transfuses from the
interior to the surface.
2. Drying should proceed uniformly at all points, otherwise
extra stresses are set up in the wood, causing warping, etc.
3. Heat should penetrate to the interior of the piece before
drying begins.
4. The humidity should be suited to the condition of the
wood at the start and reduced in the proper ratio as drying
progresses. With wet or green wood it should usually be held
uniform at a degree which will prevent the surface from
drying below its saturation point until all the free water
has evaporated, then gradually reduced to remove the
hygroscopic moisture.
5. The temperature should be uniform and as high as the
species under treatment will stand without excessive
shrinkage, collapse, or checking.
6. Rate of drying should be controlled by the amount of
humidity in the air and not by the rate of circulation,
which should be made ample at all times.
7. In drying refractory hardwoods, such as oak, best results
are obtained at a comparatively low temperature. In more
easily dried hardwoods, such as maple, and some of the more
difficult softwoods, as cypress, the process may be hastened
by a higher temperature but not above the boiling point. In
many of the softwoods, the rate of drying may be very
greatly increased by heating above the boiling point with a
large circulation of vapor at atmospheric pressure.
8. Unequal shrinkage between the exterior and interior
portions of the wood and also unequal chemical changes must
be guarded against by temperatures and humidities suited to
the species in question to prevent subsequent cupping and
warping.
9. The degree of dryness attained should conform to the use
to which the wood is put.
10. Proper piling of the material and weighting to prevent
warping are of great importance.
Requirements in a Satisfactory Dry Kiln
The requirements in a satisfactory dry kiln are:
1. Control of humidity at all times.
2. Ample air circulation at all points.
3. Uniform and proper temperatures.
In order to meet these requirements the United States Forestry Service
has designed a kiln in which the humidity, temperature, and
circulation can be controlled at all times.
Briefly, it consists of a drying chamber with a partition on either
side, making two narrow side chambers open top and bottom.
The steam pipes are in the usual position underneath the material to
be dried.
At the top of the side chambers is a spray; at the bottom are gutters
and an eliminator or set of baffle plates to separate the fine mist
from the air.
The spray accomplishes two things: It induces an increased circulation
and it regulates the humidity. This is done by regulating the
temperature of the spray water.
The air under the heating coil is saturated at whatever temperature
is required. This temperature is the dew point of the air after it
passes up into the drying chamber above the coils. Knowing the
temperature in the drying room and the dew point, the relative
humidity is thus determined.
The relative humidity is simply the ratio of the vapor pressure at the
dew point to the pressure of saturated vapor (see Fig. 30).
[Illustration: Fig. 30. Section through United States
Forestry Service Humidity-controlled Dry Kiln.]
Theory and Description of the Forestry Service Kiln
The humidities and temperatures in the piles of lumber are largely
dependent upon the circulation of air within the kiln. The temperature
and humidity within the kiln, taken alone, are no criterion of the
conditions of drying the pile of lumber if the circulation in any
portion is deficient. It is possible to have an extremely rapid
circulation of air within the dry kiln itself and yet have stagnation
within the individual piles, the air passing chiefly through open
spaces and channels. Wherever stagnation exists or the movement of air
is too sluggish the temperature will drop and the humidity increase,
perhaps to the point of saturation.
When in large kilns the forced circulation is in the opposite
direction from that induced by the cooling of the air by the lumber,
there is always more or less uncertainty as to the movement of the air
through the piles. Even with the boards placed edge-wise, with
stickers running vertically, and with the heating pipes beneath the
lumber, it was found that although the air passed upward through most
of the spaces it was actually descending through others, so that very
unequal drying resulted. While edge piling would at first thought seem
ideal for the freest circulation in an ordinary kiln with steam pipes
below, it in fact produces an indeterminate condition; air columns may
pass downward through some channels as well as upward through others,
and probably stagnate in still others. Nevertheless, edge piling is
greatly superior to flat piling where the heating system is below the
lumber.
From experiments and from study of conditions in commercial kilns the
idea was developed of so arranging the parts of the kiln and the pile
of lumber that advantage might be taken of this cooling of the air to
assist the circulation. That this can be readily accomplished without
doing away with the present features of regulation of humidity by
means of a spray of water is clear from Fig. 30, which shows a
cross-section of the improved humidity-regulated dry kiln.
In the form shown in the sketch a chamber or flue B runs through the
center near the bottom. This flue is only about 6 or 7 feet in height
and, together with the water spray F and the baffle plates DD,
constitutes the humidity-control feature of the kiln. This control of
humidity is affected by the temperature of the water used in the
spray. This spray completely saturates the air in the flue B at
whatever predetermined temperature is required. The baffle plates DD
are to separate all entrained particles of water from the air, so that
it is delivered to the heaters in a saturated condition at the
required temperature. This temperature is, therefore, the dew point of
the air when heated above, and the method of humidity control may
therefore be called the dew-point method. It is a very simple matter
by means of the humidity diagram (see Fig. 93), or by a hygrodeik
(Fig. 94), to determine what dew-point temperature is needed for any
desired humidity above the heaters.
Besides regulating the humidity the spray F also acts as an ejector
and forces circulation of air through the flue B. The heating system H
is concentrated near the outer walls, so as to heat the rising column
of air. The temperature within the drying chamber is controlled by
means of any suitable thermostat, actuating a valve on the main steam
line. The lumber is piled in such a way that the stickers slope
downward toward the sides of the kiln.
M is an auxiliary steam spray pointing downward for use at very high
temperatures. C is a gutter to catch the precipitation and conduct it
back to the pump, the water being recirculated through the sprays. G
is a pipe condenser for use toward the end of the drying operation. K
is a baffle plate for diverting the heated air and at the same time
shielding the under layers of boards from direct radiation of the
steam pipes.
The operation of the kiln is simple. The heated air rises above the
pipes HH and between the piles of lumber. As it comes in contact with
the piles, portions of it are cooled and pass downward and outward
through the layers of boards into the space between the condensers GG.
Here the column of cooled air descends into the spray flue B, where
its velocity is increased by the force of the water spray. It then
passes out from the baffle plates to the heaters and repeats the
cycle.
One of the greatest advantages of this natural circulation method is
that the colder the lumber when placed in the kiln the greater is the
movement produced, under the very conditions which call for the
greatest circulation--just the opposite of the direct-circulation
method. This is a feature of the greatest importance in winter, when
the lumber is put into the kiln in a frozen condition. One truckload
of lumber at 60 per cent moisture may easily contain over 7,000 pounds
of ice.
In the matter of circulation the kiln is, in fact, seldom
regulatory--the colder the lumber the greater the circulation
produced, with the effect increased toward the cooler and wetter
portions of the pile.
Preliminary steaming may be used in connection with this kiln, but
experiments indicate that ordinarily it is not desirable, since the
high humidity which can be secured gives as good results, and being at
as low a temperature as desired, much better results in the case of
certain difficult woods like oak, eucalyptus, etc., are obtained.
This kiln has another advantage in that its operation is entirely
independent of outdoor atmospheric conditions, except that barometric
pressure will effect it slightly.
KILN-DRYING
Remarks
Drying is an essential part of the preparation of wood for
manufacture. For a long time the only drying process used or known was
air-drying, or the exposure of wood to the gradual drying influences
of the open air, and is what has now been termed "preliminary
seasoning." This method is without doubt the most successful and
effective seasoning, because nature performs certain functions in
air-drying that cannot be duplicated by artificial means. Because of
this, hardwoods, as a rule, cannot be successfully kiln-dried green or
direct from the saw.
Within recent years, considerable interest is awakening among wood
users in the operation of kiln-drying. The losses occasioned in
air-drying and in improper kiln-drying, and the necessity for getting
material dry as quickly as possible from the saw, for shipping
purposes and also for manufacturing, are bringing about a realization
of the importance of a technical knowledge of the subject.
The losses which occur in air-drying wood, through checking, warping,
staining, and rotting, are often greater than one would suppose. While
correct statistics of this nature are difficult to obtain, some idea
may be had of the amount of degrading of the better class of lumber.
In the case of one species of soft wood, Western larch, it is commonly
admitted that the best grades fall off sixty to seventy per cent in
air-drying, and it is probable that the same is true in the case of
Southern swamp oaks. In Western yellow pine, the loss is great, and in
the Southern red gum, it is probably as much as thirty per cent. It
may be said that in all species there is some loss in air-drying, but
in some easily dried species such as spruce, hemlock, maple, etc., it
is not so great.
It would hardly be correct to state at the present time that this loss
could be entirely prevented by proper methods of kiln-drying the green
lumber, but it is safe to say that it can be greatly reduced.
It is well where stock is kiln-dried direct from the saw or knife,
after having first been steamed or boiled--as in the case of veneers,
etc.,--to get them into the kiln while they are still warm, as they
are then in good condition for kiln-drying, as the fibres of the wood
are soft and the pores well opened, which will allow of forcing the
evaporation of moisture without much damage being done to the
material.
With softwoods it is a common practice to kiln-dry direct from the
saw. This procedure, however, is ill adapted for the hardwoods, in
which it would produce such warping and checking as would greatly
reduce the value of the product. Therefore, hardwoods, as a rule, are
more or less thoroughly air-dried before being placed in the dry kiln,
where the residue of moisture may be reduced to within three or four
per cent, which is much lower than is possible by air-drying only.
It is probable that for the sake of economy, air-drying will be
eliminated in the drying processes of the future without loss to the
quality of the product, but as yet no method has been discovered
whereby this may be accomplished.
The dry kiln has been, and probably still is, one of the most
troublesome factors arising from the development of the timber
industry. In the earlier days, before power machinery for the
working-up of timber products came into general use, dry kilns were
unheard-of, air-drying or seasoning was then relied upon solely to
furnish the craftsman with dry stock from which to manufacture his
product. Even after machinery had made rapid and startling strides on
its way to perfection, the dry kiln remained practically an unknown
quantity, but gradually, as the industry developed and demand for dry
material increased, the necessity for some more rapid and positive
method of seasoning became apparent, and the subject of artificial
drying began to receive the serious attention of the more progressive
and energetic members of the craft.
Kiln-drying which is an artificial method, originated in the effort to
improve or shorten the process, by subjecting the wood to a high
temperature or to a draught of heated air in a confined space or kiln.
In so doing, time is saved and a certain degree of control over the
drying operation is secured.
The first efforts in the way of artificial drying were confined to
aiding or hastening nature in the seasoning process by exposing the
material to the direct heat from fires built in pits, over which the
lumber was piled in a way to expose it to the heat rays of the fires
below. This, of course, was a primitive, hazardous, and very
unsatisfactory method, to say the least, but it marked the first step
in the evolution of the present-day dry kiln, and in that particular
only is it deserving of mention.
Underlying Principles
In addition to marking the first step in artificial drying, it
illustrated also, in the simplest manner possible, the three
underlying principles governing all drying problems: (1) The
application of heat to evaporate or volatilize the water contained in
the material; (2) with sufficient air in circulation to carry away in
suspension the vapor thus liberated; and (3) with a certain amount of
humidity present to prevent the surface from drying too rapidly while
the heat is allowed to penetrate to the interior. The last performs
two distinct functions: (a) It makes the wood more permeable to the
passage of the moisture from the interior of the wood to the surface,
and (b) it supplies the latent heat necessary to evaporate the
moisture after it reaches the surface. The air circulation is
important in removing the moisture after it has been evaporated by the
heat, and ventilation also serves the purpose of bringing the heat in
contact with the wood. If, however, plain, dry heat is applied to the
wood, the surface will become entirely dry before the interior
moisture is even heated, let alone removed. This condition causes
"case-hardening" or "hollow-horning." So it is very essential that
sufficient humidity be maintained to prevent the surface from drying
too rapidly, while the heat is allowed to penetrate to the interior.
This humidity or moisture is originated by the evaporation from the
drying wood, or by the admission of steam into the dry kiln by the use
of steam spray pipes, and is absolutely necessary in the process of
hastening the drying of wood. With green lumber it keeps the sap near
the surface of the piece in a condition that allows the escape of the
moisture from its interior; or, in other words, it prevents the
outside from drying first, which would close the pores and cause
case-hardening.
The great amount of latent heat necessary to evaporate the water after
it has reached the surface is shown by the fact that the evaporation
of only one pound of water will extract approximately 66 degrees from
1,000 cubic feet of air, allowing the air to drop in temperature from
154 to 84 degrees Fahrenheit. In addition to this amount of heat, the
wood and the water must also be raised to the temperature at which the
drying is to be accomplished.
It matters not what type of dry kiln is used, source or application of
heating medium, these underlying principles remain the same, and must
be the first things considered in the design or selection of the
equipment necessary for producing the three essentials of drying:
Heat, humidity, and circulation.
Although these principles constitute the basis of all drying problems
and must, therefore, be continually carried in mind in the
consideration of them, it is equally necessary to have a comprehensive
understanding of the characteristics of the materials to be dried, and
its action during the drying process. All failures in the past, in the
drying of timber products, can be directly attributed to either the
kiln designer's neglect of these things, or his failure to carry them
fully in mind in the consideration of his problems.
Wood has characteristics very much different from those of other
materials, and what little knowledge we have of it and its properties
has been taken from the accumulated records of experience. The reason
for this imperfect knowledge lies in the fact that wood is not a
homogeneous material like the metals, but a complicated structure, and
so variable that one stick will behave in a manner widely different
from that of another, although it may have been cut from the same
tree.
The great variety of woods often makes the mere distinction of the
kind or species of the tree most difficult. It is not uncommon to find
men of long experience disagree as to the kind of tree a certain piece
of lumber was cut from, and, in some cases, there is even a wide
difference in the appearance and evidently the structure of timber cut
from the same tree.
Objects of Kiln-drying
The objects of kiln-drying wood may be placed under three main
headings: (1) To reduce shipping expenses; (2) to reduce the quantity
necessary to maintain in stock; and (3) to reduce losses in air-drying
and to properly prepare the wood for subsequent use. Item number 2
naturally follows as a consequence of either 1 or 3. The reduction in
weight on account of shipping expenses is of greatest significance
with the Northwestern lumbermen in the case of Douglas fir, redwood,
Western red cedar, sugar pine, bull pine, and other softwoods.
Very rapid methods of rough drying are possible with some of these
species, and are in use. High temperatures are used, and the water is
sometimes boiled off from the wood by heating above 212 degrees
Fahrenheit. These high-temperature methods will not apply to the
majority of hardwoods, however, nor to many of the softwoods.
It must first of all be recognized that the drying of lumber is a
totally different operation from the drying of a fabric or of thin
material. In the latter, it is largely a matter of evaporated
moisture, but wood is not only hygroscopic and attracts moisture from
the air, but its physical behavior is very complex and renders the
extraction of moisture a very complicated process.
An idea of its complexity may be had by mentioning some of the
conditions which must be contended with. Shrinkage is, perhaps, the
most important. This is unequal in different directions, being twice
as great tangentially as radially and fifty times as great radially as
longitudinally. Moreover, shrinkage is often unequal in different
portions of the same piece. The slowness of the transfusion of
moisture through the wood is an important factor. This varies with
different woods and greatly in different directions. Wood becomes soft
and plastic when hot and moist, and will yield more or less to
internal stresses. As some species are practically impervious to air
when wet, this plasticity of the cell walls causes them to collapse as
the water passes outward from the cell cavities. This difficulty has
given much trouble in the case of Western red cedar, and also to some
extent in redwood. The unequal shrinkage causes internal stresses in
the wood as it dries, which results in warping, checking,
case-hardening, and honeycombing. Case-hardening is one of the most
common defects in improperly dried lumber. It is clearly shown by the
cupping of the two halves when a case-hardened board is resawed.
Chemical changes also occur in the wood in drying, especially so at
higher temperatures, rendering it less hygroscopic, but more brittle.
If dried too much or at too high a temperature, the strength and
toughness is seriously reduced.
Conditions of Success
Commercial success in drying therefore requires that the substance be
exposed to the air in the most efficient manner; that the temperature
of the air be as high as the substance will stand without injury, and
that the air change or movement be as rapid as is consistent with
economical installation and operation. Conditions of success therefore
require the observance of the following points, which embody the basic
principles of the process: (1) The timber should be heated through
before drying begins. (2) The air should be very humid at the
beginning of the drying process, and be made drier only gradually. (3)
The temperature of the lumber must be maintained uniformly throughout
the entire pile. (4) Control of the drying process at any given
temperature must be secured by controlling the relative humidity, not
by decreasing the circulation. (5) In general, high temperatures
permit more rapid drying than do lower temperatures. The higher the
temperature of the lumber, the more efficient is the kiln. It is
believed that temperatures as high as the boiling point are not
injurious to most woods, providing all other fundamentally important
features are taken care of. Some species, however, are not able to
stand as high temperatures as others, and (6) the degree of dryness
attained, where strength is the prime requisite, should not exceed
that at which the wood is to be used.
Different Treatment according to Kind
The rapidity with which water may be evaporated, that is, the rate of
drying, depends on the size and shape of the piece and on the
structure of the wood. Thin stock can be dried much faster than thick,
under the same conditions of temperature, circulation, and humidity.
Pine can be dried, as a general thing, in about one third of the time
that would be required for oak of the same thickness, although the
former contains the more water of the two. Quarter-sawn oak usually
requires half again as long as plain oak. Mahogany requires about the
same time as plain oak; ash dries in a little less time, and maple,
according to the purpose for which it is intended, may be dried in one
fifth the time needed for oak, or may require a slightly longer
treatment. For birch, the time required is from one half to two
thirds, and for poplar and basswood, from, one fifth to one third that
required for oak.
All kinds and thicknesses of lumber cannot be dried at the same time
in the same kiln. It is manifest that green and air-dried lumber,
dense and porous lumber, all require different treatment. For
instance, Southern yellow pine when cut green from the log will stand
a very high temperature, say 200 degrees Fahrenheit, and in fact this
high temperature is necessary together with a rapid circulation of air
in order to neutralize the acidity of the pitch which causes the wood
to blue and discolor. This lumber requires to be heated up immediately
and to be kept hot throughout the length of the kiln. Hence the kiln
must not be of such length as to allow of the air being too much
cooled before escaping.
Temperature depends
While it is true that a higher temperature can be carried in the kiln
for drying pine and similar woods, this does not altogether account
for the great difference in drying time, as experience has taught us
that even when both woods are dried in the same kiln, under the same
conditions, pine will still dry much faster, proving thereby that the
structure of the wood itself affects drying.
The aim of all kiln designers should be to dry in the shortest
possible time, without injury to the material. Experience has
demonstrated that high temperatures are very effective in evaporating
water, regardless of the degree of humidity, but great care must be
exercised in using extreme temperatures that the material to be dried
is not damaged by checking, case-hardening, or hollow-horning.
The temperature used should depend upon the species and condition of
the material when entering the kiln. In general, it is advantageous to
have as high a temperature as possible, both for economy of operation
and speed of drying, but the physical properties of the wood will
govern this.
Many species cannot be dried satisfactorily at high temperatures on
account of their peculiar behavior. This is particularly so with green
lumber.
Air-dried wood will stand a relatively higher temperature, as a rule,
than wet or green wood. In drying green wood direct from the saw, it
is usually best to start with a comparatively low temperature, and not
raise the temperature until the wood is nearly dry. For example, green
maple containing about 60 per cent of its dry weight in water should
be started at about 120 degrees Fahrenheit and when it reaches a
dryness of 25 per cent, the temperature may be raised gradually up to
190 degrees.
It is exceedingly important that the material be practically at the
same temperature throughout if perfect drying is to be secured. It
should be the same temperature in the center of a pile or car as on
the outside, and the same in the center of each individual piece of
wood as on its surface. This is the effect obtained by natural
air-drying. The outside atmosphere and breezes (natural air
circulation) are so ample that the heat extracted for drying does not
appreciably change the temperature.
When once the wood has been raised to a high temperature through and
through and especially when the surface has been rendered most
permeable to moisture, drying may proceed as rapidly as it can be
forced by artificial circulation, provided the heat lost from the wood
through vaporization is constantly replaced by the heat of the kiln.
It is evident that to secure an even temperature, a free circulation
of air must be brought in contact with the wood. It is also evident
that in addition to heat and a circulation of air, the air must be
charged with a certain amount of moisture to prevent surface drying or
case-hardening.
There are some twenty-five different makes of dry kilns on the market,
which fulfill to a varying degree the fundamental requirements.
Probably none of them succeed perfectly in fulfilling all.
It is well to have the temperature of a dry kiln controlled by a
thermostat which actuates the valve on the main steam supply pipe. It
is doubly important to maintain a uniform temperature and avoid
fluctuations in the dry kiln, since a change in temperature will
greatly alter the relative humidity.
In artificial drying, temperatures of from 150 to 180 degrees
Fahrenheit are usually employed. Pine, spruce, cypress, cedar, etc.,
are dried fresh from the saw, allowing four days for 1-inch stuff.
Hardwoods, especially oak, ash, maple, birch, sycamore, etc., are
usually air-seasoned for three to six months to allow the first
shrinkage to take place more gradually, and are then exposed to the
above temperatures in the kiln for about six to ten days for 1-inch
stuff, other dimensions in proportion.
Freshly cut poplar and cottonwood are often dried direct from the saw
in a kiln. By employing lower temperatures, 100 to 120 degrees
Fahrenheit, green oak, ash, etc., can be seasoned in dry kilns without
much injury to the material.
Steaming and sweating the wood is sometimes resorted to in order to
prevent checking and case-hardening, but not, as has been frequently
asserted, to enable the material to dry.
Air Circulation
Air circulation is of the utmost importance, since no drying whatever
can take place when it is lacking. The evaporation of moisture
requires heat and this must be supplied by the circulating air.
Moreover, the moisture laden air must be constantly removed and fresh,
drier air substituted. Probably this is the factor which gives more
trouble in commercial operations than anything else, and the one which
causes the greatest number of failures.
It is necessary that the air circulate through every part of the kiln
and that the moving air come in contact with every portion of the
material to be dried. In fact, the humidity is dependent upon the
circulation. If the air stagnates in any portion of the pile, then the
temperature will drop and the humidity rise to a condition of
saturation. Drying will not take place at this portion of the pile and
the material is apt to mould and rot.
The method of piling the material on trucks or in the kiln, is
therefore, of extreme importance. Various methods are in use. Ordinary
flat piling is probably the poorest. Flat piling with open chimney
spaces in the piles is better. But neither method is suitable for a
kiln in which the circulation is mainly vertical.
Edge piling with stickers running vertically is in use in kilns when
the heating coils are beneath. This is much better.
Air being cooled as it comes in contact with a pile of material,
becomes denser, and consequently tends to sink. Unless the material to
be dried is so arranged that the air can pass gradually downward
through the pile as it cools, poor circulation is apt to result.
In edge-piled lumber, with the heating system beneath the piles, the
natural tendency of the cooled air to descend is opposed by the hot
air beneath which tends to rise. An indeterminate condition is thus
brought about, resulting in non-uniform drying. It has been found that
air will rise through some layers and descend through others.
Humidity
Humidity is of prime importance because the rate of drying and
prevention of checking and case-hardening are largely dependent
thereon. It is generally true that the surface of the wood should not
dry more rapidly than the moisture transfuses from the center of the
piece to its surface, otherwise disaster will result. As a sufficient
amount of moisture is removed from the wood to maintain the desired
humidity, it is not good economy to generate moisture in an outside
apparatus and force it into a kiln, unless the moisture in the wood is
not sufficient for this purpose; in that case provision should be made
for adding any additional moisture that may be required.
The rate of evaporation may best be controlled by controlling the
amount of vapor present in the air (relative humidity); it should not
be controlled by reducing the air circulation, since a large
circulation is needed at all times to supply the necessary heat.
The humidity should be graded from 100 per cent at the receiving end
of the kiln, to whatever humidity corresponds with the desired degree
of dryness at the delivery end.
The kiln should be so designed that the proper degree may be
maintained at its every section.
A fresh piece of sapwood will lose weight in boiling water and can
also be dried to quite an extent in steam. This proves conclusively
that a high degree of humidity does not have the detrimental effect on
drying that is commonly attributed to it. In fact, a proper degree of
humidity, especially in the loading or receiving end of a kiln, is
just as necessary to good results in drying as getting the proper
temperature.
Experiments have demonstrated also that injury to stock in the way of
checking, warping, and hollow-horning always develops immediately
after the stock is taken into the kiln, and is due to the degree of
humidity being too low. The receiving end of the kiln should always be
kept moist, where the stock has not been steamed before being put into
the kiln. The reason for this is simple enough. When the air is too
dry it tends to dry the outside of the material first--which is termed
"case-hardening"--and in so doing shrinks and closes up the pores of
the wood. As the stock is moved down the kiln, it absorbs a
continually increasing amount of heat, which tends to drive off the
moisture still present in the center of the stock. The pores on the
outside having been closed up, there is no exit for the vapor or steam
that is being rapidly formed in the center. It must find its way out
some way, and in doing so sets up strains, which result either in
checking, warping, or hollow-horning. If the humidity had been kept
higher, the outside of the material would not have dried so quickly,
and the pores would have remained open for the exit of moisture from
the interior of the wood, and this trouble would have been avoided.
Where the humidity is kept at a high point in the receiving end of the
kiln, a higher rate of temperature may also be carried, and in that
way the drying process is hastened with comparative safety.
It is essential, therefore, to have an ample supply of heat through
the convection currents of the air; but in the case of wood the rate
of evaporation must be controlled, else checking will occur. This can
be done by means of the relative humidity, as stated before. It is
clear now that when the air--or, more properly speaking, the space--is
completely saturated no evaporation can take place at the given
temperature. By reducing the humidity, evaporation takes place more
and more rapidly.
Another bad feature of an insufficient and non-uniform supply of heat
is that each piece of wood will be heated to the evaporating point on
the outer surface, the inside remaining cool until considerable drying
has taken place from the surface. Ordinarily in dry kilns high
humidity and large circulation of air are antitheses to one another.
To obtain the high humidity the circulation is either stopped
altogether or greatly reduced, and to reduce the humidity a greater
circulation is induced by opening the ventilators or otherwise
increasing the draft. This is evidently not good practice, but as a
rule is unavoidable in most dry kilns of present make. The humidity
should be raised to check evaporation without reducing the circulation
if possible.
While thin stock, such as cooperage and box stuff is less inclined to
give trouble by undue checking than 1-inch and thicker, one will find
that any dry kiln will give more uniform results and, at the same
time, be more economical in the use of steam, when the humidity and
temperature is carried at as high a point as possible without injury
to the material to be dried.
Any well-made dry kiln which will fulfill the conditions required as
to circulation and humidity control should work satisfactorily; but
each case must be studied by itself, and the various factors modified
to suit the peculiar conditions of the problem in hand. In every new
case the material should be constantly watched and studied and, if
checking begins, the humidity should be increased until it stops. It
is not reducing the circulation, but adding the necessary moisture to
the air, that should be depended on to prevent checking. For this
purpose it is well to have steam jets in the kiln so that if needed
they are ready at hand.
Kiln-drying
There are two distinct ways of handling material in dry kilns. One way
is to place the load of lumber in a chamber where it remains in the
same place throughout the operation, while the conditions of the
drying medium are varied as the drying progresses. This is the
"apartment" kiln or stationary method. The other is to run the lumber
in at one end of the chamber on a wheeled truck and gradually move it
along until the drying process is completed, when it is taken out at
the opposite end of the kiln. It is the usual custom in these kilns to
maintain one end of the chamber moist and the other end dry. This is
known as the "progressive" type of kiln, and is the one most commonly
used in large operations.
It is, however, the least satisfactory of the two where careful drying
is required, since the conditions cannot be so well regulated and the
temperatures and humidities are apt to change with any change of wind.
The apartment method can be arranged so that it will not require any
more kiln space or any more handling of lumber than the progressive
type. It does, however, require more intelligent operation, since the
conditions in the drying chamber must be changed as the drying
progresses. With the progressive type the conditions, once properly
established, remain the same.
To obtain draft or circulation three methods are in use--by forced
draft or a blower usually placed outside the kiln, by ventilation, and
by internal circulation and condensation. A great many patents have
been taken out on different methods of ventilation, but in actual
operation few kilns work exactly as intended. Frequently the air moves
in the reverse direction for which the ventilators were planned.
Sometimes a condenser is used in connection with the blower and the
air is recirculated. It is also--and more satisfactorily--used with
the gentle internal-gravity currents of air.
Many patents have been taken out for heating systems. The differences
among these, however, have more to do the mechanical construction than
with the process of drying. In general, the heating is either direct
or indirect. In the former steam coils are placed in the chamber with
the lumber, and in the latter the air is heated by either steam coils
or a furnace before it is introduced into the drying chamber.
Moisture is sometimes supplied by means of free steam jets in the kiln
or in the entering air; but more often the moisture evaporated from
the lumber is relied upon to maintain the humidity necessary.
A substance becomes dry by the evaporation of its inherent moisture
into the surrounding space. If this space be confined it soon becomes
saturated and the process stops. Hence, constant change is necessary
in order that the moisture given off may be continually carried away.
In practice, air movement, is therefore absolutely essential to the
process of drying. Heat is merely a useful accessory which serves to
decrease the time of drying by increasing both the rate of evaporation
and the absorbing power of the surrounding space.
It makes no difference whether this space is a vacuum or filled with
air; under either condition it will take up a stated weight of vapor.
From this it appears that the vapor molecules find sufficient space
between the molecules of air. But the converse is not true, for
somewhat less air will be contained in a given space saturated with
vapor than in one devoid of moisture. In other words the air does not
seem to find sufficient space between the molecules of vapor.
If the temperature of the confined space be increased, opportunity
will thereby be provided for the vaporization of more water, but if it
be decreased, its capacity for moisture will be reduced and visible
water will be deposited. The temperature at which this takes place is
known as the "dew-point" and depends upon the initial degree of
saturation of the given space; the less the relative saturation the
lower the dew-point.
Careful piling of the material to be dried, both in the yard and dry
kiln, is essential to good results in drying.
Air-dried material is not dry, and its moisture is too unevenly
distributed to insure good behavior after manufacture.
It is quite a difficult matter to give specific or absolute correct
weights of any species of timber when thoroughly or properly dried, in
order that one may be guided in these kiln operations, as a great deal
depends upon the species of wood to be dried, its density, and upon
the thickness which it has been cut, and its condition when entering
the drying chamber.
Elm will naturally weigh less than beech, and where the wood is
close-grained or compact it will weigh more than coarse-grained wood
of the same species, and, therefore, no set rules can be laid down, as
good judgment only should be used, as the quality of the drying is not
purely one of time. Sometimes the comparatively slow process gives
excellent results, while to rush a lot of stock through the kiln may
be to turn it out so poorly seasoned that it will not give
satisfaction when worked into the finished product. The mistreatment
of the material in this respect results in numerous defects, chief
among which are warping and twisting, checking, case-hardening, and
honeycombing, or, as sometimes called, hollow-horning.
Since the proportion of sap and heartwood varies with size, age,
species, and individual trees, the following figures as regards weight
must be regarded as mere approximations:
POUNDS OF WATER LOST IN DRYING 100 POUNDS OF GREEN WOOD IN THE KILN
=========================================================================
|Sapwood or | Heartwood
|outer part | or interior
=========================================================================
| |
(1) Pine, cedar, spruce, and fir | 45-65 | 16-25
(2) Cypress, extremely variable | 50-65 | 18-60
(3) Poplar, cottonwood, and basswood | 60-65 | 40-60
(4) Oak, beech, ash, maple, birch, elm, hickory,| |
chestnut, walnut, and sycamore | 40-50 | 30-40
=========================================================================
The lighter kinds have the most water in the sapwood; thus sycamore
has more water than hickory, etc.
The efficiency of the drying operations depends a great deal upon the
way in which, the lumber is piled, especially when the humidity is not
regulated. From the theory of drying it is evident that the rate of
evaporation in dry kilns where the humidity is not regulated depends
entirely upon the rate of circulation, other things being equal.
Consequently, those portions of the wood which receive the greatest
amount of air dry the most rapidly, and vice versa. The only way,
therefore, in which anything like uniform drying can take place is
where the lumber is so piled that each portion of it comes in contact
with the same amount of air.
In the Forestry Service kiln (Fig. 30), where the degree of relative
humidity is used to control the rate of drying, the amount of
circulation makes little difference, provided it exceeds a certain
amount. It is desirable to pile the lumber so as to offer as little
frictional resistance as possible and at the same time secure uniform
circulation. If circulation is excessive in any place it simply means
waste of energy but no other injury to the lumber.
The best method of piling is one which permits the heated air to pass
through the pile in a somewhat downward direction. The natural
tendency of the cooled air to descend is thus taken advantage of in
assisting the circulation in the kiln. This is especially important
when cold or green lumber is first introduced into the kiln. But even
when the lumber has become warmed the cooling due to the evaporation
increases the density of the mixture of the air and vapor.
Kiln-drying Gum
The following article was published by the United States Forestry
Service as to the best method of kiln-drying gum:
=Piling.=--Perhaps the most important factor in good kiln-drying,
especially in the case of the gums, is the method of piling. It is our
opinion that proper and very careful piling will greatly reduce the
loss due to warping. A good method of piling is to place the lumber
lengthwise of the kiln and on an incline cross-wise. The warm air
should rise at the higher side of the pile and descend between the
courses of lumber. The reason for this is very simple and the
principle has been applied in the manufacture of the best ice boxes
for some time. The most efficient refrigerators are iced at the side,
the ice compartment opening to the cooling chamber at the top and
bottom. The warm air from above is cooled by melting the ice. It then
becomes denser and settles down into the main chamber. The articles in
the cooling room warm the air as they cool, so it rises to the top and
again comes in contact with the ice, thus completing the cycle. The
rate of this natural circulation is automatically regulated by the
temperature of the articles in the cooling chamber and by the amount
of ice in the icing compartment; hence the efficiency of such a box is
high.
Now let us apply this principle to the drying of lumber. First we must
understand that as long as the lumber is moist and drying, it will
always be cooler than the surrounding air, the amount of this
difference being determined by the rate of drying and the moisture in
the wood. As the lumber dries, its temperature gradually rises until
it is equal to that of the air, when perfect dryness results. With
this fact in mind it is clear that the function of the lumber in a
kiln is exactly analogous to that of the ice in an ice box; that is,
it is the cooling agent. Similarly, the heating pipes in a dry kiln
bring about the same effect as the articles of food in the ice box in
that they serve to heat the air. Therefore, the air will be cooled by
the lumber, causing it to pass downward through the piles. If the
heating units are placed at the sides of the kiln, the action of the
air in a good ice box is duplicated in the kiln. The significant point
in this connection is that, the greener and colder the lumber, the
faster is the circulation. This is a highly desirable feature.
A second vital point is that as the wood becomes gradually drier the
circulation automatically decreases, thus resulting in increased
efficiency, because there is no need for circulation greater than
enough to maintain the humidity of the air as it leaves the lumber
about the same as it enters. Therefore, we advocate either the
longitudinal side-wise inclined pile or edge stacking, the latter
being much preferable when possible. Of course the piles in our kiln
were small and could not be weighted properly, so the best results as
to reducing warping were not obtained.
=Preliminary Steaming.=--Because the fibres of the gums become plastic
while moist and hot without causing defects, it is desirable to heat
the air-dried lumber to about 200 degrees Fahrenheit in saturated
steam at atmospheric pressure in order to reduce the warping. This
treatment also furnishes a means of heating the lumber very rapidly.
It is probably a good way to stop the sap-staining of green lumber, if
it is steamed while green. We have not investigated the other effects
of steaming green gum, however, so we hesitate to recommend it.
Temperatures as high as 210 degrees Fahrenheit were used with no
apparent harm to the material. The best result was obtained with the
temperature of 180 degrees Fahrenheit, after the first preliminary
heating in steam to 200 degrees Fahrenheit. Higher temperatures may be
used with air-dried gum, however.
The best method of humidity control proved to be to reduce the
relative humidity of the air from 100 per cent (saturated steam) very
carefully at first and then more rapidly to 30 per cent in about four
days. If the change is too marked immediately after the steaming
period, checking will invariably result. Under these temperature and
humidity conditions the stock was dried from 15 per cent moisture,
based on the dry wood weight, to 6 per cent in five days' time. The
loss due to checking was about 5 per cent, based on the actual footage
loss, not on commercial grades.
=Final Steaming.=--From time to time during the test runs the material
was resawed to test for case-hardening. The stock dried in five days
showed slight case-hardening, so it was steamed at atmospheric
pressure for 36 minutes near the close of the run, with the result
that when dried off again the stresses were no longer present. The
material from one run was steamed for three hours at atmospheric
pressure and proved very badly case-hardened, but in the reverse
direction. It seems possible that by testing for the amount of
case-hardening one might select a final steaming period which would
eliminate all stresses in the wood.
Kiln-drying of Green Red Gum
The following article was published by the United States Forestry
Service on the kiln-drying of green red gum:
A short time ago fifteen fine, red-gum logs 16 feet long were received
from Sardis, Miss. They were in excellent condition and quite green.
It has been our belief that if the gum could be kiln-dried directly
from the saw, a number of the difficulties in seasoning might be
avoided. Therefore, we have undertaken to find out whether or not such
a thing is feasible. The green logs now at the laboratory are to be
used in this investigation. One run of a preliminary nature has just
been made, the method and results of which I will now tell.
This method was really adapted to the drying of Southern pine, and one
log of the green gum was cut into 1-inch stock and dried with the
pine. The heartwood contained many knots and some checks, although it
was in general of quite good quality. The sapwood was in fine
condition and almost as white as snow.
This material was edge-stacked with one crosser at either end and one
at the center, of the 16-foot board. This is sufficient for the pine,
but was absolutely inadequate for drying green gum. A special
shrinkage take-up was applied at the three points. The results proved
very interesting in spite of the warping which was expected with but
three crossers in 16 feet. The method of circulation described was
used. It is our belief that edge piling is best for this method.
This method of kiln-drying depends on the maintenance of a high
velocity of slightly superheated steam through the lumber. In few
words, the object is to maintain the temperature of the vapor as it
leaves the lumber at slightly above 212 degrees Fahrenheit. In order
to accomplish this result, it is necessary to maintain the high
velocity of circulation. As the wood dries, the superheat may be
increased until a temperature of 225 degrees or 230 degrees Fahrenheit
of the exit air is recorded.
The 1-inch green gum was dried from 20.1 per cent to 11.4 per cent
moisture, based on the dry wood weight in 45 hours. The loss due to
checking was 10 per cent. Nearly every knot in the heartwood was
checked, showing that as the knots could be eliminated in any case,
this loss might not be so great. It was significant that practically
all of the checking occurred in the heartwood. The loss due to warping
was 22 per cent. Of course this was large; but not nearly enough
crossers were used for the gum. It is our opinion that this loss due
to warping can be very much reduced by using at least eight crossers
and providing for taking up of the shrinkage. A feature of this
process which is very important is that the method absolutely prevents
all sap staining.
Another delightful surprise was the manner in which the superheated
steam method of drying changed the color of the sapwood from pure
white to a beautifully uniform, clean-looking, cherry red color which
very closely resembles that of the heartwood. This method is not new
by any means, as several patents have been granted on the steaming of
gum to render the sapwood more nearly the color of the heartwoods. The
method of application in kiln-drying green gum we believe to be new,
however. Other methods for kiln-drying this green stock are to be
tested until the proper process is developed. We expect to have
something interesting to report in the near future.[1]
[Footnote 1: The above test was made at the United States
Forestry Service Laboratory, Madison, Wis.]
SECTION XII
TYPES OF DRY KILNS
DIFFERENT TYPES OF DRY KILNS
Dry kilns as in use to-day are divided into two classes: The "pipe" or
"moist-air" kiln, in which natural draft is relied upon for
circulation and, the "blower" or "hot blast" kiln, in which the
circulation is produced by fans or blowers. Both classes have their
adherents and either one will produce satisfactory results if properly
operated.
The "Blower" or "Hot Blast" Kiln
The blower kiln in its various types has been in use so long that it
is hardly necessary to give to it a lengthy introduction. These kilns
at their inauguration were a wonderful improvement over the old style
"bake-oven" or "sweat box" kiln then employed, both on account of the
improved quality of the material and the rapidity at which it was
dried.
These blower kilns have undergone steady improvement, not only in the
apparatus and equipment, but also in their general design, method of
introducing air, and provision for controlling the temperature and
humidity. With this type of kiln the circulation is always under
absolute control and can be adjusted to suit the conditions, which
necessarily vary with the conditions of the material to be dried and
the quantity to be put through the kiln.
In either the blower or moist-air type of dry kiln, however, it is
absolutely essential, in order to secure satisfactory results, both as
to rapidity in drying and good quality of stock, that the kiln be so
designed that the temperature and humidity, together with circulation,
are always under convenient control. Any dry kiln in which this has
not been carefully considered will not give the desired results.
In the old style blower kiln, while the circulation and temperature
was very largely under the operator's control, it was next to
impossible to produce conditions in the receiving end of the kiln so
that the humidity could be kept at the proper point. In fact, this was
one reason why the natural draft, or so-called moist-air kiln was
developed.
The advent of the moist-air kiln served as an education to kiln
designers and manufacturers, in that it has shown conclusively the
value of a proper degree of humidity in the receiving end of any
progressive dry kiln, and it has been of special benefit also in that
it gave the manufacturers of blower kilns an idea as to how to improve
the design of their type of kiln to overcome the difficulty referred
to in the old style blower kilns. This has now been remedied, and in a
decidedly simple manner, as is usually the case with all things that
possess merit.
It was found that by returning from one third to one half of the moist
air _after_ having passed through the kiln back to the fan room and by
mixing it with the fresh and more or less dry air going into the
drying room, that the humidity could be kept under convenient control.
The amount of air that can be returned from a kiln of this class
depends upon three things: (1) The condition of the material when
entering the drying room; (2) the rapidity with which the material is
to be dried; and (3) the condition of the outside atmosphere. In the
winter season it will be found that a larger proportion of air may be
returned to the drying room than in summer, as the air during the
winter season contains considerably less moisture and as a consequence
is much drier. This is rather a fortunate coincidence, as, when the
kiln is being operated in this manner, it will be much more economical
in its steam consumption.
In the summer season, when the outside atmosphere is saturated to a
much greater extent, it will be found that it is not possible to
return as great a quantity of air to the drying room, although there
have been instances of kilns of this class, which in operation have
had all the air returned and found to give satisfactory results. This
is an unusual condition, however, and can only be accounted for by
some special or peculiar condition surrounding the installation.
In some instances, the desired amount of humidity in a blower type of
kiln is obtained by the addition of a steam spray in the receiving end
of the kiln, much in the same manner as that used in the moist-air
kilns. This method is not as economical as returning the
moisture-laden air from the drying room as explained in the preceding
paragraph.
With the positive circulation that may be obtained in a blower kiln,
and with the conditions of temperature and humidity under convenient
control, this type of kiln has the elements most necessary to produce
satisfactory drying in the quickest possible elapsed time.
It must not be inferred from this, however, that this class of dry
kiln may be installed and satisfactory results obtained regardless of
how it is handled. A great deal of the success of any dry kiln--or any
other apparatus, for that matter--depends upon intelligent operation.
Operation of the "Blower" Dry Kiln
It is essential that the operator be supplied with proper facilities
to keep a record of the material as it is placed into the drying room,
and when it is taken out. An accurate record should be kept of the
temperature every two or three hours, for the different thicknesses
and species of lumber, that he may have some reliable data to guide
him in future cases.
Any man possessing ordinary intelligence can operate dry kilns and
secure satisfactory results, providing he will use good judgment and
follow the basic instructions as outlined below:
1. When cold and before putting into operation, heat the
apparatus slowly until all pipes are hot, then start the fan
or blower, gradually bringing it up to its required speed.
2. See that _all_ steam supply valves are kept wide open,
unless you desire to lengthen the time required to dry the
material.
3. When using exhaust steam, the valve from the header
(which is a separate drip, independent of the trap
connection) must be kept wide open, but must be closed when
live steam is used on that part of the heater.
4. The engines as supplied by the manufacturers are
constructed to operate the fan or blower at a proper speed
with its throttle valve wide open, and with not less than 80
pounds pressure of steam.
5. If the return steam trap does not discharge regularly, it
is important that it be opened and thoroughly cleaned and
the valve seat re-ground.
6. As good air circulation is as essential as the proper
degree of heat, and as the volume of air and its contact
with the material to be dried depends upon the volume
delivered by the fan or blower, it is necessary to maintain
a regular and uniform speed of the engine.
7. Atmospheric openings must always be maintained in the fan
or heater room for fresh air supply.
8. Successful drying cannot be accomplished without ample
and free circulation of air at all times.
If the above instructions are fully carried out, and good judgment
used in the handling and operation of the blower kiln, no difficulties
should be encountered in successfully drying the materials at hand.
The "Pipe" or "Moist-air" Dry Kiln
While in the blower class of dry kiln, the circulation is obtained by
forced draft with the aid of fans or blowers, in the Moist-air kilns
(see Fig. 31); the circulation is obtained by natural draft only,
aided by the manipulation of dampers installed at the receiving end of
the drying room, which lead to vertical flues through a stack to the
outside atmosphere.
The heat in these kilns is obtained by condensing steam in coils of
pipe, which are placed underneath the material to be dried. As the
degree of heat required, and steam pressure govern the amount of
radiation, there are several types of radiating coils. In Fig. 32 will
be seen the Single Row Heating Coils for live or high pressure steam,
which are used when the low temperature is required. Figure 33 shows
the Double (or 2) Row Heating Coils for live or high pressure steam.
This apparatus is used when a medium temperature is required. In Fig.
34 will be seen the Vertical Type Heating Coils which is recommended
where exhaust or low-pressure steam is to be used, or may be used with
live or high-pressure steam when high temperatures are desired.
[Illustration: Fig. 31. Section through a typical Moist-air
Dry Kiln.]
These heating coils are usually installed in sections, which permit
any degree of heat from the minimum to the maximum to be maintained by
the elimination of, or the addition of, any number of heating
sections. This gives a dry kiln for the drying of green softwoods, or
by shutting off a portion of the radiating coils--thus reducing the
temperature--a dry kiln for drying hardwoods, that will not stand the
maximum degree of heat.
[Illustration: Fig. 32. Single Pipe Heating Apparatus for Dry
Kilns, arranged for the Use of Live Steam. For Low
Temperatures.]
[Illustration: Fig. 33. Double Pipe Heating Apparatus for Dry
Kilns, arranged for the Use of Live Steam. For Medium
Temperatures.]
In the Moist-air or Natural Draft type of dry kiln, any degree of
humidity, from clear and dry to a dense fog may be obtained; this is
in fact, the main and most important feature of this type of dry kiln,
and the most essential one in the drying of hardwoods.
It is not generally understood that the length of a kiln has any
effect upon the quantity of material that may be put through it, but
it is a fact nevertheless that long kilns are much more effective, and
produce a better quality of stock in less time than kilns of shorter
length.
Experience has proven that a kiln from 80 to 125 feet in length will
produce the best results, and it should be the practice, where
possible, to keep them within these figures. The reason for this is
that in a long kiln there is a greater drop in temperature between the
discharge end and the green or receiving end of the kiln.
It is very essential that the conditions in the receiving end of the
kiln, as far as the temperature and humidity are concerned, must go
hand in hand.
It has also been found that in a long kiln the desired conditions may
be obtained with higher temperatures than with a shorter kiln;
consequently higher temperatures may be carried in the discharge end
of the kiln, thereby securing greater rapidity in drying. It is not
unusual to find that a temperature of 200 degrees Fahrenheit is
carried in the discharge end of a long dry kiln with safety, without
in any way injuring the quality of the material, although, it would be
better not to exceed 180 degrees in the discharge end, and about 120
degrees in the receiving or green end in order to be on the safe side.
Operation of the "Moist-air" Dry Kiln
To obtain the best results these kilns should be kept in continuous
operation when once started, that is, they should be operated
continuously day and night. When not in operation at night or on
Sundays, and the kiln is used to season green stock direct from the
saw, the large doors at both ends of the kiln should be opened wide,
or the material to be dried will "sap stain."
[Illustration: Fig. 34. Vertical Pipe Heating Apparatus for
Dry Kilns; may be used in Connection with either Live or
Exhaust Steam for High or Low Temperatures.]
It is highly important that the operator attending any drying
apparatus keep a minute and accurate record of the condition of the
material as it is placed into the drying room, and its final condition
when taken out.
Records of the temperature and humidity should be taken frequently and
at stated periods for the different thicknesses and species of
material, in order that he may have reliable data to guide him in
future operations.
The following facts should be taken into consideration when operating
the Moist-air dry kiln:
1. Before any material has been placed in the drying room,
the steam should be turned into the heating or radiating
coils, gradually warming them, and bringing the temperature
in the kiln up to the desired degree.
2. Care should be exercised that there is sufficient
humidity in the receiving or loading end of the kiln, in
order to guard against checking, case-hardening, etc.
Therefore it is essential that the steam spray at the
receiving or loading end of the kiln be properly
manipulated.
3. As the temperature depends principally upon the pressure
of steam carried in the boilers, maintain a steam pressure
of not less than 80 pounds at all times; it may range as
high as 100 pounds. The higher the temperature with its
relatively high humidity the more rapidly the drying will be
accomplished.
4. Since air circulation is as essential as the proper
degree of heat, and as its contact with the material to be
dried depends upon its free circulation, it is necessary
that the dampers for its admittance into, and its exit from,
the drying room be efficiently and properly operated.
Successful drying cannot be accomplished without ample and
free circulation of air at all times during the drying
process.
If the above basic principles are carefully noted and followed out,
and good common sense used in the handling and operation of the kiln
apparatus, no serious difficulties should arise against the successful
drying of the materials at hand.
Choice of Drying Method
At this point naturally arises the question: Which of the two classes
of dry kilns, the "Moist-air" or "Blower" kiln is the better adapted
for my particular needs?
This must be determined entirely by the species of wood to be dried,
its condition when it goes into the kiln, and what kind of finished
product is to be manufactured from it.
Almost any species of hardwood which has been subjected to
air-seasoning for three months or more may be dried rapidly and in the
best possible condition for glue-jointing and fine finishing with a
"Blower" kiln, but green hardwood, direct from the saw, can only be
successfully dried (if at all) in a "Moist-air" kiln.
Most furniture factories have considerable bent stock which must of
necessity be thoroughly steamed before bending. By steaming, the
initial process of the Moist-air kiln has been consummated. Hence, the
Blower kiln is better adapted to the drying of such stock than the
Moist-air kiln would be, as the stock has been thoroughly soaked by
the preliminary steaming, and all that is required is sufficient heat
to volatilize the moisture, and a strong circulation of air to remove
it as it comes to the surface.
The Moist-air kiln is better adapted to the drying of tight cooperage
stock, while the Blower kiln is almost universally used throughout the
slack cooperage industry for the drying of its products.
For the drying of heavy timbers, planks, blocks, carriage stock, etc.,
and for all species of hardwood thicker than one inch, the Moist-air
kiln is undoubtedly the best.
Both types of kilns are equally well adapted to the drying of 1-inch
green Norway and white pine, elm, hemlock, and such woods as are used
in the manufacture of flooring, ceiling, siding, shingles, hoops, tub
and pail stock, etc.
The selection of one or the other for such work is largely matter of
personal opinion.
Kilns of Different Types
All dry kilns as in use to-day are divided as to method of drying into
two classes:
The "Pipe" or "Moist-air" kiln;
The "Blower" or "Hot Blast" kiln;
both of which have been fully explained in a previous article.
The above two classes are again subdivided into five different types
of dry kilns as follows:
The "Progressive" kiln;
The "Apartment" kiln;
The "Pocket" kiln;
The "Tower" kiln;
The "Box" kiln.
The "Progressive" Dry Kiln
Dry kilns constructed so that the material goes in at one end and is
taken out at the opposite end are called Progressive dry kilns, from
the fact that the material gradually progresses through the kiln from
one stage to another while drying (see Fig. 31).
In the operation of the Progressive kiln, the material is first
subjected to a sweating or steaming process at the receiving or
loading end of the kiln with a low temperature and a relative high
humidity. It then gradually progresses through the kiln into higher
temperatures and lower humidities, as well as changes of air
circulation, until it reaches the final stage at the discharge end of
the kiln.
Progressive kilns, in order to produce the most satisfactory results,
especially in the drying of hardwoods or heavy softwood timbers,
should be not less than 100 feet in length (see Fig. 35).
In placing this type of kiln in operation, the following instructions
should be carefully followed:
When steam has been turned into the heating coils, and the kiln is
fairly warm, place the first car of material to be dried in the drying
room--preferably in the morning--about 25 feet from the kiln door on
the receiving or loading end of the kiln, blocking the wheels so that
it will remain stationary.
[Illustration: Fig. 35. Exterior View of Four Progressive Dry
Kilns, each 140 Feet long by 18 Feet wide. Cross-wise piling,
fire-proof construction.]
Five hours later, or about noon, run in the second car and stop it
about five feet from the first one placed in the drying room. Five
hours later, or in the evening push car number two up against the
first car; then run in car number three, stopping it about five feet
from car number two.
On the morning of the second day, push car number three against the
others, and then move them all forward about 25 feet, and then run in
car number four, stopping it about five feet from the car in advance
of it. Five hours later, or about noon, run in car number five and
stop it about five feet from car number four. In the evening or about
five hours later, push these cars against the ones ahead, and run in
loaded car number six, stopping it about five feet from the preceding
car.
On the morning of the third day, move all the cars forward about six
feet; then run in loaded car number seven stop it about four feet from
the car preceding it. Five hours later or about noon push this car
against those in advance of it, and run in loaded car number eight
moving all cars forward about six feet, and continue in this manner
until the full complement of cars have been placed in the kiln. When
the kiln has been filled, remove car number one and push all the
remaining cars forward and run in the next loaded car, and continue in
this manner as long as the kiln is in operation.
As the temperature depends principally upon the pressure of steam,
maintain a steam pressure of not less than 80 pounds at all times; it
may range up to as high as 100 pounds. The higher the temperature with
a relatively higher humidity the more rapidly the drying will be
accomplished.
If the above instructions are carried out, the temperatures,
humidities, and air circulation properly manipulated, there should be
complete success in the handling of this type of dry kiln.
The Progressive type of dry kiln is adapted to such lines of
manufacture that have large quantities of material to kiln-dry where
the species to be dried is of a similiar nature or texture, and does
not vary to any great extent in its thickness, such, for instance, as:
Oak flooring plants;
Maple flooring plants;
Cooperage plants;
Large box plants;
Furniture factories; etc.
In the selection of this kind of dry kiln, consideration should be
given to the question of ground space of sufficient length or
dimension to accommodate a kiln of proper length for successful
drying.
The "Apartment" Dry Kiln
The Apartment system of dry kilns are primarily designed for the
drying of different kinds or sizes of material at the same time, a
separate room or apartment being devoted to each species or size when
the quantity is sufficient (see Fig. 36).
These kilns are sometimes built single or in batteries of two or more,
generally not exceeding 40 or 50 feet in length with doors and
platforms at both ends the same as the Progressive kilns; but in
operation each kiln is entirely filled at one loading and then closed,
and the entire contents dried at one time, then emptied and again
recharged.
Any number of apartments may be built, and each apartment may be
arranged to handle any number of cars, generally about three or four,
or they may be so constructed that the material is piled directly upon
the floor of the drying room.
[Illustration: Fig. 36. Exterior View of Six Apartment Dry
Kilns, each 10 Feet wide by 52 Feet long, End-wise Piling.
They are entirely of fire-proof construction and equipped
with double doors (Hussey asbestos outside and canvas
inside), and are also equipped with humidity and air control
dampers, which may be operated from the outside without
opening the kiln doors, which is a very good feature.]
When cars are used, it is well to have a transfer car at each end of
the kilns, and stub tracks for holding cars of dry material, and for
the loading of the unseasoned stock, as in this manner the kilns may
be kept in full operation at all times.
In this type of dry kiln the material receives the same treatment and
process that it would in a Progressive kiln. The advantages of
Apartment kilns is manifest where certain conditions require the
drying of numerous kinds as well as thicknesses of material at one and
the same time. This method permits of several short drying rooms or
apartments so that it is not necessary to mix hardwoods and softwoods,
or thick and thin material in the same kiln room.
In these small kilns the circulation is under perfect control, so that
the efficiency is equal to that of the more extensive plants, and will
readily appeal to manufacturers whose output calls for the prompt and
constant seasoning of a large variety of small stock, rather than a
large volume of material of uniform size and grade.
Apartment kilns are recommended for industries where conditions
require numerous kinds and thicknesses of material to be dried, such
as:
Furniture factories;
Piano factories;
Interior woodwork mills;
Planing mills; etc.
The "Pocket" Dry Kiln
"Pocket" dry kilns (see Fig. 37) are generally built in batteries of
several pockets. They have the tracks level and the lumber goes in and
out at the same end. Each drying room is entirely filled at one time,
the material is dried and then removed and the kiln again recharged.
The length of "Pocket" kilns ranges generally from 14 feet to about 32
feet.
The interior equipment for this type of dry kiln is arranged very
similiar to that used in the Apartment kiln. The heating or radiating
coils and steam spray jets extend the whole length of the drying room,
and are arranged for the use of either live or exhaust steam, as
desired.
Inasmuch as Pocket kilns have doors at one end only, this feature
eliminates a certain amount of door exposure, which conduces towards
economy in operation.
In operating Pocket kilns, woods of different texture and thickness
should be separated and placed in different drying rooms, and each
kiln adjusted and operated to accommodate the peculiarities of the
species and thickness of the material to be dried.
[Illustration: Fig. 37. Exterior View of Five Pocket Dry
Kilns, built in Two Batteries with the Front of each Set
facing the other, and a Transfer System between. They are
also equipped with the asbestos doors.]
Naturally, the more complex the conditions of manufacturing wood
products in any industry, the more difficult will be the proper
drying of same. Pocket kilns, are, therefore, recommended for
factories having several different kinds and thicknesses of material
to dry in small quantities of each, such as:
Planing mills;
Chair factories;
Furniture factories;
Sash and door factories; etc.
The "Tower" Dry Kiln
The so-called "Tower" dry kiln (see Fig. 38) is designed for the rapid
drying of small stuff in quantities. Although the general form of
construction and the capacity of the individual bins or drying rooms
may vary, the same essential method of operation is common to all.
That is, the material itself, such as wooden novelties, loose staves,
and heading for tubs, kits, and pails, for box stuff, kindling wood,
etc., is dumped directly into the drying rooms from above, or through
the roof, in such quantities as effectually to fill the bin, from
which it is finally removed when dry, through the doors at the bottom.
These dry kilns are usually operated as "Blower" kilns, the heating
apparatus is generally located in a separate room or building adjacent
to the main structure or drying rooms, and arranged so that the hot
air discharged through the inlet duct (see illustration) is thoroughly
distributed beneath a lattice floor upon which rests the material to
be dried. Through this floor the air passes directly upward, between
and around the stock, and finally returns to the fan or heating room.
This return air duct is so arranged that by means of dampers, leading
from each drying room, the air may be returned in any quantity to the
fan room where it is mixed with fresh air and again used. This is one
of the main features of economy of the blower system of drying, as by
the employment of this return air system, considerable saving may be
made in the amount of steam required for drying.
[Illustration: Fig. 38. Exterior and Sectional View of a
Battery of Tower Dry Kilns. This is a "Blower" or "Hot Blast"
type, and shows the arrangement of the fan blower, engine,
etc. This type of dry kin is used principally for the
seasoning of small, loose material.]
The lattice floors in this type of dry kiln are built on an incline,
which arrangement materially lessens the cost, and increases the
convenience with which the dried stock may be removed from the bins or
drying rooms.
In operation, the material is conveyed in cars or trucks on an
overhead trestle--which is inclosed--from which the material to be
dried is dumped directly into the drying rooms or bins, through
hoppers arranged for that purpose thereby creating considerable saving
in the handling of the material to be dried into the kiln. The entire
arrangement thus secures the maximum capacity, with a minimum amount
of floor space, with the least expense. Of course, the higher these
kilns are built, the less relative cost for a given result in the
amount of material dried.
In some instances, these kilns are built less in height and up against
an embankment so that teamloads of material may be run directly onto
the roof of the kilns, and dumped through the hoppers into the drying
rooms or bins, thus again reducing to a minimum the cost of this
handling.
The return air duct plays an important part in both of these methods
of filling, permitting the air to become saturated to the maximum
desired, and utilizing much of the heat contained therein, which would
otherwise escape to the atmosphere.
The "Tower" kiln is especially adapted to factories of the following
class:
Sawmills;
Novelty factories;
Woodenware factories;
Tub and pail factories; etc.
The "Box" Dry Kiln
The "Box" kiln shown in Figure 39 is an exterior view of a kiln of
this type which is 20 feet wide, 19 feet deep, and 14 feet high, which
is the size generally used when the space will permit.
Box kilns are used mostly where only a small quantity of material is
to be dried. They are not equipped with trucks or cars, the material
to be dried being piled upon a raised platform inside the drying
room. This arrangement, therefore, makes them of less cost than the
other types of dry kilns.
They are particularly adapted to any and all species and size of
lumber to be dried in very small quantities.
[Illustration: Fig. 39. Exterior view of the Box Dry Kiln.
This particular kiln is 20 feet wide, 19 feet deep and 14
feet high. Box kilns are used mostly where only a small
amount of kiln-dried lumber of various sizes is required.
They are not equipped with trucks or cars, and therefore cost
less to construct than any other type of dry kiln.]
In these small kilns the circulation is under perfect control, so that
the efficiency is equal to that of the more extensive plants.
These special kilns will readily appeal to manufacturers, whose output
calls for the prompt and constant seasoning of a large variety of
small stock, rather than a large volume material of uniform size and
grade.
SECTION XIII
DRY KILN SPECIALTIES
KILN CARS AND METHOD OF LOADING
Within recent years, the edge-wise piling of lumber (see Figs. 40 and
41), upon kiln cars has met with considerable favor on account of its
many advantages over the older method of flat piling. It has been
proven that lumber stacked edge-wise dries more uniformly and rapidly,
and with practically no warping or twisting of the material, and that
it is finally discharged from the dry kiln in a much better and
brighter condition. This method of piling also considerably increases
the holding and consequent drying capacities of the dry kiln by reason
of the increased carrying capacities of the kiln cars, and the shorter
period of time required for drying the material.
[Illustration: Fig. 40. Car Loaded with Lumber on its Edges
by the Automatic Stacker, to go into the Dry Kiln cross-wise.
Equipped with two edge piling kiln trucks.]
In Figures 42 and 43 are shown different views of the automatic lumber
stacker for edge-wise piling of lumber on kiln cars. Many users of
automatic stackers report that the grade of their lumber is raised to
such an extent that the system would be profitable for this reason
alone, not taking into consideration the added saving in time and
labor, which to anyone's mind should be the most important item.
[Illustration: Fig. 41. Car Loaded with Lumber on its Edges
by the Automatic Stacker, to go into the Dry Kiln end-wise.
The bunks on which the lumber rests are channel steel. The
end sockets are malleable iron and made for I-beam stakes.]
In operation, the lumber is carried to these automatic stackers on
transfer chains or chain conveyors, and passes on to the stacker
table. When the table is covered with boards, the "lumber" lever is
pulled by the operator, which raises a stop, preventing any more
lumber leaving the chain conveyor. The "table" lever then operates the
friction drive and raises the table filled with the boards to a
vertical position. As the table goes up, it raises the latches, which
fall into place behind the piling strips that had been previously laid
on the table. When the table returns to the lower position, a new set
of piling strips are put in place on the table, and the stream of
boards which has been accumulating on the conveyor chain are again
permitted to flow onto the table. As each layer of lumber is added,
the kiln car is forced out against a strong tension. When the car is
loaded, binders are put on over the stakes by means of a powerful
lever arrangement.
[Illustration: Fig. 42. The above illustration shows the
construction of the Automatic Lumber Stacker for edge piling
of lumber to go into the dry kiln end-wise.]
[Illustration: Fig. 43. The above illustration shows the
construction of the Automatic Lumber Stacker for edge piling
of lumber to go into the dry kiln cross-wise.]
[Illustration: Fig. 44. The above illustration shows a
battery of Three Automatic Lumber Stackers.]
[Illustration: Fig. 45. The above illustration shows another
battery of Three Automatic Lumber Stackers.]
[Illustration: Fig. 46. Cars Loaded with Lumber on its Edges
by the Automatic Lumber Stackers.]
After leaving the dry kilns, the loaded car is transferred to the
unstacker (see Fig. 47). Here it is placed on the unstacker car which,
by means of a tension device, holds the load of lumber tight against
the vertical frame of the unstacker. The frame of the unstacker is
triangular and has a series of chains. Each chain has two special
links with projecting lugs. The chains all travel in unison. The lug
links engage a layer of boards, sliding the entire layer vertically,
and the boards, one at a time, fall over the top of the unstacker
frame onto the inclined table, and from there onto conveyor chains
from which they may be delivered to any point desired, depending upon
the length and direction of the chain conveyor.
With these unstackers one man can easily unload a kiln car in twenty
minutes or less.
[Illustration: Fig. 47. The Lumber Unstacker Car, used for
unloading cars of Lumber loaded by the Automatic Stacker.]
[Illustration: Fig. 48. The Lumber Unstacker Car and
Unstacker, used for unloading Lumber loaded by the Automatic
Stacker.]
The experience of many users prove that these edge stacking machines
are not alike. This is important, because there is one feature of edge
stacking that must not be overlooked. Unless each layer of boards is
forced into place by power and held under a strong pressure, much
slack will accumulate in an entire load, and the subsequent handling
of the kiln cars, and the effect of the kiln-drying will loosen up the
load until there is a tendency for the layers to telescope. And unless
the boards are held in place rigidly and with strong pressure they
will have a tendency to warp.
[Illustration: Fig. 49. The above illustration shows method
of loading kiln cars with veneer on its edges by the use of
the Tilting Platform.]
A kiln car of edge-stacked lumber, properly piled, is made up of
alternate solid sheets of lumber and vertical open-air spaces, so that
the hot air and vapors rise naturally and freely through the lumber,
drying both sides of the board evenly. The distribution of the heat
and moisture being even and uniform, the drying process is naturally
quickened, and there is no opportunity or tendency for the lumber to
warp.
In Figure 49 will be seen a method of loading kiln cars with veneer on
edge by the use of a tilting platform. On the right of the
illustration is seen a partially loaded kiln car tilted to an angle of
45 degrees, to facilitate the placing of the veneer on the car. At
the left is a completely loaded car ready to enter the dry kiln.
Gum, poplar, and pine veneers are satisfactorily dried in this manner
in from 8 to 24 hours.
In Figure 50 will be seen method of piling lumber on the flat,
"cross-wise" of the dry kiln when same has three tracks.
[Illustration: Fig. 50. Method of Loading lumber on its Flat,
cross-wise of the Dry Kiln when same has Three Tracks.]
In Figure 51 will be seen another method of piling lumber on the flat,
"cross-wise" of the dry kiln when same has three tracks.
In Figure 52 will be seen method of piling lumber on the flat,
"end-wise" of the dry kiln when same has two tracks.
In Figure 53 will be seen another method of piling lumber on the flat,
"end-wise" of the dry kiln when same has two tracks.
In Figure 54 will be seen method of piling slack or tight barrel
staves "cross-wise" of the kiln when same has three tracks.
In Figure 55 will be seen another method of piling slack or tight
barrel staves "cross-wise" of the dry kiln when same has three tracks.
In Figure 56 will be seen method of piling small tub or pail staves
"cross-wise" of the dry kiln when same has two tracks.
In Figure 57 will be seen method of piling bundled staves "cross-wise"
of the dry kiln when same has two tracks.
[Illustration: Fig. 51. Method of loading Lumber on its Flat,
cross-wise of the Dry Kiln when same has Three Tracks.]
[Illustration: Fig. 52. Method of loading Lumber on its Flat,
end-wise of the Dry Kiln by the Use of the Single-sill or
Dolly Truck.]
[Illustration: Fig. 53. Method of loading Lumber on its Flat,
end-wise of the Dry Kiln by the Use of the Double-sill
Truck.]
[Illustration: Fig. 54. Method of loading Kiln Car with Tight
or Slack Barrel Staves cross-wise of Dry Kiln.]
[Illustration: Fig. 55. Method of loading Kiln Car with Tight
or Slack Barrel Staves cross-wise of Dry Kiln.]
[Illustration: Fig. 56. Method of loading Kiln Car with Tub
or Pail Staves cross-wise of Dry Kiln.]
[Illustration: Fig. 57. Method of loading Kiln Car with
Bundled Staves cross-wise of Dry Kiln.]
In Figure 58 will be seen method of piling shingles "cross-wise" of
dry kiln when same has three tracks.
In Figure 59 will be seen another method of piling shingles
"cross-wise" of the dry kiln when same has three tracks.
[Illustration: Fig. 58. Method of loading Kiln Car with
Shingles cross-wise of Dry Kiln.]
[Illustration: Fig. 59. Method of loading Kiln Car with
Shingles cross-wise of Dry Kiln.]
In Figure 60 will be seen method of piling shingles "end-wise" of the
dry kiln when same has two tracks.
In Figure 61 will be seen a kiln car designed for handling short tub
or pail staves through a dry kiln.
[Illustration: Fig. 60. Car loaded with 100,000 Shingles.
Equipped with four long end-wise piling trucks and to go into
dry kiln end-wise.]
[Illustration: Fig. 61. Kiln Car designed for handling Short
Tub or Pail Staves through a Dry Kiln.]
In Figure 62 will be seen a kiln car designed for short piece stock
through a dry kiln.
In Figure 63 will be seen a type of truck designed for the handling of
stave bolts about a stave mill or through a steam box.
In Figure 64 will be seen another type of truck designed for the
handling of stave bolts about a stave mill or through a steam box.
In Figure 65 will be seen another type of truck designed for the
handling of stave bolts about a stave mill or through a steam box.
In Figure 66 will be seen another type of truck designed for the
handling of stave bolts about a stave mill or through a steam box.
In Figure 67 will be seen another type of truck designed for the
handling of stave bolts about a stave mill or through a steam box.
In Figure 68 will be seen another type of truck designed for the
handling of stave bolts about a stave mill or through a steam box.
In Figure 69 will be seen the Regular 3-rail Transfer Car designed for
the handling of 2-rail kiln cars which have been loaded "end-wise."
In Figure 70 will be seen another type of Regular 3-rail Transfer Car
designed for the handling of 2-rail kiln cars which have been loaded
"end-wise."
In Figure 71 will be seen a Specially-designed 4-rail Transfer Car for
2-rail kiln cars which have been built to accommodate extra long
material to be dried.
In Figure 72 will be seen the Regular 2-rail Transfer Car designed for
the handling of 3-rail kiln cars which have been loaded "cross-wise."
In Figure 73 will be seen another type of Regular 2-rail Transfer Car
designed for the handling of 3-rail kiln cars which have been loaded
"cross-wise."
In Figure 74 will be seen the Regular 2-rail Underslung type of
Transfer Car designed for the handling of 3-rail kiln cars which have
been loaded "cross-wise." Two important features in the construction
of this transfer car make it extremely easy in its operation. It has
extra large wheels, diameter 13-1/2 inches, and being underslung, the
top of its rails are no higher than the other types of transfer cars.
Note the relative size of the wheels in the illustration, yet the car
is only about 10 inches in height.
[Illustration: Fig. 62. Kiln Car Designed for handling Short
Piece Stock through a Dry Kiln.]
[Illustration: Fig. 63. A Stave Bolt Truck.]
[Illustration: Fig. 64. A Stave Bolt Truck.]
[Illustration: Fig. 65. A Stave Bolt Truck.]
[Illustration: Fig. 66. A Stave Bolt Truck.]
[Illustration: Fig. 67. A Stave Bolt Truck.]
[Illustration: Fig. 68. A Stave Bolt Truck.]
[Illustration: Fig. 69. A Regular 3-Rail Transfer Truck.]
[Illustration: Fig. 70. A Regular 3-Rail Transfer Truck.]
[Illustration: Fig. 71. A Special 4-Rail Transfer Truck.]
[Illustration: Fig. 72. A Regular 2-Rail Transfer Truck.]
[Illustration: Fig. 73. A Regular 2-Rail Transfer Truck.]
[Illustration: Fig. 74. A Regular 2-Rail Underslung Transfer
Truck.]
[Illustration: Fig. 75. A Regular 3-Rail Underslung Transfer
Truck.]
In Figure 75 will be seen the Regular 3-rail Underslung type of
Transfer Car designed for the handling of 2-rail kiln cars which have
been loaded "end-wise." This car also has the important features of
large diameter wheels and low rail construction, which make it very
easy in its operation.
[Illustration: Fig. 76. A Special 2-Rail Flexible Transfer
Truck.]
In Figure 76 will be seen the Special 2-rail Flexible type of Transfer
Car designed for the handling of 3-rail kiln cars which have been
loaded "cross-wise." This car is equipped with double the usual number
of wheels, and by making each set of trucks a separate unit (the front
and rear trucks being bolted to a steel beam with malleable iron
connection), a slight up-and-down movement is permitted, which enables
this transfer car to adjust itself to any unevenness in the track,
which is a very good feature.
In Figure 77 will be seen the Regular Transfer Car designed for the
handling of stave bolt trucks.
In Figure 78 will be seen another type of Regular Transfer Car
designed for the handling of stave bolt trucks.
In Figure 79 will be seen a Special Transfer Car designed for the
handling of stave bolt trucks.
[Illustration: Fig. 77. A Regular Transfer Car for handling
Stave Bolt Trucks.]
[Illustration: Fig. 78. A Regular Transfer Car for handling
Stave Bolt Trucks.]
[Illustration: Fig. 79. A Special Transfer Car for handling
Stave Bolt Trucks.]
In Figure 80 will be seen the Regular Channel-iron Kiln Truck designed
for edge piling "cross-wise" of the dry kiln.
In Figure 81 will be seen another type of Regular Channel-iron Kiln
Truck designed for edge piling "cross-wise" of the dry kiln.
[Illustration: Fig. 80. A Regular Channel-iron Kiln Truck.]
[Illustration: Fig. 81. A Regular Channel-iron Kiln Truck.]
In Figure 82 will be seen the Regular Channel-iron Kiln Truck designed
for flat piling "end-wise" of the dry kiln.
[Illustration: Fig. 82. A Regular Channel-iron Kiln Truck.]
[Illustration: Fig. 83. A Regular Channel-iron Kiln Truck.]
[Illustration: Fig. 84. A Regular Single-sill or Dolly Kiln
Truck.]
In Figure 83 will be seen the Regular Channel-iron Kiln Truck with
I-Beam cross-pieces designed for flat piling "end-wise" of the dry
kiln.
In Figure 84 will be seen the Regular Small Dolly Kiln Truck designed
for flat piling "end-wise" of the dry kiln.
Different Types of Kiln Doors
In Figure 85 will be seen the Asbestos-lined Door. The construction of
this kiln door is such that it has no tendency to warp or twist. The
framework is solid and the body is made of thin slats placed so that
the slat on either side covers the open space of the other with
asbestos roofing fabric in between. This makes a comparatively light
and inexpensive door, and one that absolutely holds the heat. These
doors may be built either swinging, hoisting, or sliding.
[Illustration: Fig. 85. An Asbestos-lined Kiln Door of the
Hinge Type.]
In Figure 86 will be seen the Twin Carrier type of door hangers with
doors loaded and rolling clear of the opening.
[Illustration: Fig. 86. Twin Carrier with Kiln Door loaded
and rolling clear of Opening.]
[Illustration: Fig. 87. Twin Carriers for Kiln Doors 18 to 35
Feet wide.]
In Figure 87 will be seen the Twin Carrier for doors 18 to 35 feet
wide, idle on a section of the track.
In Figure 88 will be seen another type of carrier for kiln doors.
In Figure 89 will be seen the preceding type of kiln door carrier in
operation.
In Figure 90 will be seen another type of carrier for kiln doors.
In Figure 91 will be seen kiln doors seated, wood construction,
showing 3-1/2" × 5-3/4" inch-track timbers and trusses, supported on
4-inch by 6-inch jamb posts. "T" rail track, top and side, inclined
shelves on which the kiln door rests. Track timber not trussed on
openings under 12 feet wide.
[Illustration: Fig. 88. Kiln Door Carrier engaged to Door
Ready for lifting.]
In Figure 92 will be seen kiln doors seated, fire-proof construction,
showing 12-inch, channel, steel lintels, 2" × 2" steel angle mullions,
track brackets bolted to the steel lintels and "T" rail track. No
track timbers or trusses used.
[Illustration: Fig. 89. Kiln Door Carrier shown on Doors of
Wood Construction.]
[Illustration: Fig. 90. Kiln Door Construction with Door
Carrier out of Sight.]
[Illustration: Fig. 91. Kiln Door Construction. Doors Seated.
Wood Construction.]
[Illustration: Fig. 92. Kiln Door Construction. Doors Seated.
Fire-proof Construction.]
SECTION XIV
HELPFUL APPLIANCES IN KILN-DRYING
The Humidity Diagram
[Illustration: Fig. 93. The United States Forest Service
Humidity Diagram for determination of Absolute Humidities.
Dew Points and Vapor Pressures; also Relative Humidities by
means of Wet and Dry-Bulb Thermometer, for any temperatures
and change in temperature.]
Some simple means of determining humidities and changes in humidity
brought about by changes in temperature in the dry kiln without the
use of tables is almost a necessity. To meet this requirement the
United States Forestry Service has devised the Humidity Diagram shown
in Figure 93. It differs in several respects from the hydrodeiks now
in use.
The purpose of the humidity diagram is to enable the dry-kiln operator
to determine quickly the humidity conditions and vapor pressure, as
well as the changes which take place with changes of temperature. The
diagram above is adapted to the direct solution of problems of this
character without recourse to tables or mathematical calculations.
The humidity diagram consists of two distinct sets of curves on the
same sheet. One set, the convex curves, is for the determination of
relative humidity of wet-and-dry-bulb hygrometer or psychrometer; the
other, the concave curves, is derived from the vapor pressures and
shows the amount of moisture per cubic foot at relative humidities and
temperatures when read at the dew-point. The latter curves, therefore,
are independent of all variables affecting the wet-bulb readings. They
are proportional to vapor pressures, not to density, and, therefore,
may be followed from one temperature to another with correctness. The
short dashes show the correction (increase or decrease) which is
necessary in the relative humidity, read from the convex curves, with
an increase or decrease from the normal barometric pressure of 30
inches, for which the curves have been plotted. This correction,
except for very low temperatures, is so small that it may usually be
disregarded.
The ordinates, or vertical distances, are relative humidity expressed
in per cent of saturation, from 0 per cent at the bottom to 100 per
cent at the top. The abscissae, or horizontal distances, are
temperatures in degrees Fahrenheit from 30 degrees below zero, at the
left, to 220 degrees above, at the right.
Examples of Use
The application of the humidity diagram can best be understood by
sample problems. These problems also show the wide range of conditions
to which the diagram will apply.
EXAMPLE 1. To find the relative humidity by use of
wet-and-dry-bulb hygrometer or psychrometer:
Place the instrument in a strong circulation of air, or wave
it to and fro. Read the temperature of the dry bulb and the
wet, and subtract. Find on the horizontal line the
temperature shown by the dry-bulb thermometer. Follow the
vertical line from this point till it intersects with the
convex curve marked with the difference between the wet and
dry readings. The horizontal line passing through this
intersection will give the relative humidity.
Example: Dry bulb 70°, wet bulb 62°, difference 8°. Find 70°
on the horizontal line of temperature. Follow up the
vertical line from 70° until it intersects with the convex
curve marked 8°. The horizontal line passing through this
intersection shows the relative humidity to be 64 per cent.
EXAMPLE 2. To find how much water per cubic foot is
contained in the air:
Find the relative humidity as in example 1. Then the nearest
concave curve gives the weight of water in grains per cubic
foot when the air is cooled to the dew-point. Using the same
quantities as in example 1, this will be slightly more than
5 grains.
EXAMPLE 3. To find the amount of water required to saturate
air at a given temperature:
Find on the top line (100 per cent humidity) the given
temperature; the concave curve intersecting at or near this
point gives the number of grains per cubic foot.
(Interpolate, if great accuracy is desired.)
EXAMPLE 4. To find the dew-point:
Obtain the relative humidity as in example 1. Then follow up
parallel to the nearest concave curve until the top
horizontal (indicating 100 per cent relative humidity) is
reached. The temperature on this horizontal line at the
point reached will be the dew-point.
Example: Dry bulb 70°, wet bulb 62°. On the vertical line
for 70° find the intersection with the hygrometer (convex)
curve for 8°. This will be found at nearly 64 per cent
relative humidity. Then follow up parallel with the vapor
pressure (concave) curve marked 5 grains to its intersection
at the top of the chart with the 100 per cent humidity line.
This gives the dew-point as 57°.
EXAMPLE 5. To find the change in the relative humidity
produced by a change in temperature:
Example: The air at 70° Fahr. is found to contain 64 per
cent humidity; what will be its relative humidity if heated
to 150° Fahr.? Starting from the intersection of the
designated humidity and temperature coordinates, follow the
vapor-pressure curve (concave) until it intersects the 150°
temperature ordinate. The horizontal line then reads 6 per
cent relative humidity. The same operation applies to
reductions in temperature. In the above example what is the
humidity at 60°? Following parallel to the same curve in the
opposite direction until it intersects the 60° ordinate
gives 90 per cent; at 57° it becomes 100 per cent, reaching
the dew-point.
EXAMPLE 6. To find the amount of condensation produced by
lowering the temperature:
Example: At 150° the wet bulb reads 132°. How much water
would be condensed if the temperature were lowered to 70°?
The intersection of the hygrometer curve for 18° (150°-132°)
with temperature line for 150° shows a relative humidity of
60 per cent. The vapor-pressure curve (concave) followed up
to the 100 per cent relative humidity line shows 45 grains
per cubic foot at the dew-point, which corresponds to a
temperature of 130°. At 70° it is seen that the air can
contain but 8 grains per cubic foot (saturation).
Consequently, there will be condensed 45 minus 8, or 37
grains per cubic foot of space measured at the dew-point.
EXAMPLE 7. To find the amount of water required to produce
saturation by a given rise in temperature:
Example: Take the values given in example 5. The air at the
dew-point contains slightly over 5 grains per cubic foot. At
150° it is capable of containing 73 grains per cubic foot.
Consequently, 73-5=68 grains of water which can be
evaporated per cubic foot of space at the dew-point when the
temperature is raised to 150°. But the latent heat necessary
to produce evaporation must be supplied in addition to the
heat required to raise the air to 150°.
EXAMPLE 8. To find the amount of water evaporated during a
given change of temperature and humidity:
Example: At 70° suppose the humidity is found to be 64 per
cent and at 150° it is found to be 60 per cent. How much
water has been evaporated per cubic foot of space? At 70°
temperature and 64 per cent humidity there are 5 grains of
water present per cubic foot at the dew-point (example 2).
At 150° and 60 per cent humidity there are 45 grains
present. Therefore, 45-5=40 grains of water which have been
evaporated per cubic foot of space, figuring all volumes at
the dew-point.
EXAMPLE 9. To correct readings of the hygrometer for changes
in barometric pressure:
A change of pressure affects the reading of the wet bulb.
The chart applies at a barometric pressure of 30 inches,
and, except for great accuracy, no correction is generally
necessary.
Find the relative humidity as usual. Then look for the
nearest barometer line (indicated by dashes). At the end of
each barometer line will be found a fraction which
represents the proportion of the relative humidity already
found, which must be added or subtracted for a change in
barometric pressure. If the barometer reading is less than
30 inches, add; if greater than 30 inches, subtract. The
figures given are for a change of 1 inch; for other changes
use proportional amounts. Thus, for a change of 2 inches use
twice the indicated ratio; for half an inch use half, and so
on.
Example: Dry bulb 67°, wet bulb 51°, barometer 28 inches.
The relative humidity is found, by the method given in
example 1, to equal 30 per cent. The barometric line--gives
a value of 3/100H for each inch of change. Since the
barometer is 2 inches below 30, multiply 3/100H by 2, giving
6/100H. The correction will, therefore, be 6/100 of 30,
which equals 1.8. Since the barometer is below 30, this is
to be added, giving a corrected relative humidity of 31.8
per cent.
This has nothing to do with the vapor pressure (concave)
curves, which are independent of barometric pressure, and
consequently does not affect the solution of the previous
problems.
EXAMPLE 10. At what temperature must the condenser be
maintained to produce a given humidity?
Example: Suppose the temperature in the drying room is to be
kept at 150° Fahr., and a humidity of 80 per cent is
desired. If the humidity is in excess of 80 per cent the air
must be cooled to the dew-point corresponding to this
condition (see example 4), which in this case is 141.5°.
Hence, if the condenser cools the air to this dew point the
required condition is obtained when the air is again heated
to the initial temperature.
EXAMPLE 11. Determination of relative humidity by the
dew-point:
The quantity of moisture present and relative humidity for
any given temperature may be determined directly and
accurately by finding the dew-point and applying the concave
(vapor-pressure) curves. This does away with the necessity
for the empirical convex curves and wet-and-dry-bulb
readings. To find the dew-point some form of apparatus,
consisting essentially of a thin glass vessel containing a
thermometer and a volatile liquid, such as ether, may be
used. The vessel is gradually cooled through the evaporation
of the liquid, accelerated by forcing air through a tube
until a haze or dimness, due to condensation from the
surrounding air, first appears upon the brighter outer
surface of the glass. The temperature at which the haze
first appears is the dew-point. Several trials should be
made for this temperature determination, using the average
temperature at which the haze appears and disappears.
To determine the relative humidity of the surrounding air by
means of the dew-point thus determined, find the concave
curve intersecting the top horizontal (100 per cent
relative humidity) line nearest the dew-point temperature.
Follow parallel with this curve till it intersects the
vertical line representing the temperature of the
surrounding air. The horizontal line passing through this
intersection will give the relative humidity.
Example: Temperature of surrounding air is 80; dew-point is
61; relative humidity is 53 per cent.
The dew-point determination is, however, not as convenient
to make as the wet-and-dry-bulb hygrometer readings.
Therefore, the hygrometer (convex) curves are ordinarily
more useful in determining relative humidities.
The Hygrodeik
In Figure 94 will be seen the Hygrodeik. This instrument is used to
determine the amount of moisture in the atmosphere. It is a very
useful instrument, as the readings may be taken direct with accuracy.
To find the relative humidity in the atmosphere, swing the index hand
to the left of the chart, and adjust the sliding pointer to that
degree of the wet-bulb thermometer scale at which the mercury stands.
Then swing the index hand to the right until the sliding pointer
intersects the curved line, which extends downwards to the left from
the degree of the dry-bulb thermometer scale, indicated by the top of
the mercury column in the dry-bulb tube.
At that intersection, the index hand will point to the relative
humidity on scale at bottom of chart (for example see Fig. 94). Should
the temperature indicated by the wet-bulb thermometer be 60 degrees,
and that of the dry-bulb 70 degrees, the index hand will indicate
humidity 55 degrees, when the pointer rests on the intersecting line
of 60 degrees and 80 degrees.
The Recording Hygrometer
In Figure 95 is shown the Recording Hygrometer complete with wet and
dry bulbs, two connecting tubes and two recording pens and special
moistening device for supplying water to the wet bulb.
This equipment is designed particularly for use in connection with dry
rooms and dry kilns and is arranged so that the recording instrument
and the water supply bottle may be installed outside of the dry kiln
or drying room, while the wet and dry bulbs are both installed inside
the room or kiln at the point where it is desired to measure the
humidity. This instrument records on a weekly chart the humidity for
each hour of the day, during the entire week.
[Illustration: Fig. 94. The Hygrodeik.]
The Registering Hygrometer
In Figure 96 is shown the Registering Hygrometer, which consists of
two especially constructed thermometers. The special feature of the
thermometers permits placing the instrument in the dry kiln without
entering the drying room, through a small opening, where it is left
for about 20 minutes.
[Illustration: Fig. 95. The Recording Hygrometer, Complete
with Wet and Dry Bulbs. This instrument records on a weekly
chart the humidity for each hour of the day, during the
entire week.]
The temperature of both the dry and wet bulbs are automatically
recorded, and the outside temperature will not affect the thermometers
when removed from the kiln. From these recorded temperatures, as shown
when the instrument is removed from the kiln, the humidity can be
easily determined from a simple form of chart which is furnished free
by the makers with each instrument.
The Recording Thermometer
[Illustration: Fig. 96. The Registering Hygrometer.]
[Illustration: Fig. 97. The Recording Thermometer.]
In Figure 97 is shown the Recording Thermometer for observing and
recording the temperatures within a dry kiln, and thus obtaining a
check upon its operation. This instrument is constructed to record
automatically, upon a circular chart, the temperatures prevailing
within the drying room at all times of the day and night, and serves
not only as a means of keeping an accurate record of the operation of
the dry kiln, but as a valuable check upon the attendant in charge of
the drying process.
[Illustration: Fig. 98. The Registering Thermometer.]
[Illustration: Fig. 99. The Recording Steam-Pressure Gauge.]
The Registering Thermometer
In Figure 98 is shown the Registering Thermometer, which is a less
expensive instrument than that shown in Figure 97, but by its use the
maximum and minimum temperatures in the drying room during a given
period can be determined.
The Recording Steam Gauge
In Figure 99 is shown the Recording Steam Pressure Gauge, which is
used for accurately recording the steam pressures kept in the boilers.
This instrument may be mounted near the boilers, or may be located at
any distance necessary, giving a true and accurate record of the
fluctuations of the steam pressure that may take place within the
boilers, and is a check upon both the day and night boiler firemen.
The Troemroid Scalometer
In Figure 100 is shown the Troemroid Scalometer. This instrument is a
special scale of extreme accuracy, fitted with agate bearings with
screw adjustment for balancing. The beam is graduated from 0 to 2
ounces, divided into 100 parts, each division representing 1-50th of
an ounce; and by using the pointer attached to the beam weight, the
1-100th part of an ounce can be weighed.
[Illustration: Fig. 100. The Troemroid Scalometer.]
The percentage table No. II has a range from one half of 1 per cent to
30 per cent and is designed for use where extremely fine results are
needed, or where a very small amount of moisture is present. Table
No. III ranges from 30 per cent up to 90 per cent. These instruments
are in three models as described below.
MODEL A. (One cylinder) ranges from 1/2 of 1 per cent to 30
per cent and is to be used for testing moisture contents in
kiln-dried and air-dried lumber.
MODEL B. (Two cylinders) ranges from 1/2 of 1 per cent up to
90 per cent and is to be used for testing the moisture
contents of kiln-dried, air-dried, and green lumber.
MODEL C. (One cylinder) ranges from 30 per cent to 90 per
cent and is applicable to green lumber only.
=Test Samples.=--The green boards and all other boards intended for
testing should be selected from boards of fair average quality. If
air-dried, select one about half way up the height of the pile of
lumber. If kiln-dried, two thirds the height of the kiln car. Do not
remove the kiln car from the kiln until after the test. Three of four
test pieces should be cut from near the middle of the cross-wise
section of the board, and 1/8 to 3/16 inch thick. Remove the
superfluous sawdust and splinters. When the test pieces are placed on
the scale pan, be sure their weight is less than two ounces and more
than 1-3/4 ounces. If necessary, use two or more broken pieces. It is
better if the test pieces can be cut off on a fine band saw.
=Weighing.=--Set the base of the scale on a level surface and accurately
balance the scale beam. Put the test pieces on the scale pan and note
their weight on the lower edge of the beam. Set the indicator point on
the horizontal bar at a number corresponding to this weight, which may
be found on the cylinder at the top of the table.
Dry the test pieces on the Electric Heater (Fig. 101) 30 to 40
minutes, or on the engine cylinder two or three hours. Weigh them at
once and note the weight. Then turn the cylinder up and at the left of
it under the small pointer find the number corresponding to this
weight. The percentage of moisture lost is found directly under
pointer on the horizontal bar first mentioned. The lower portion on
the cylinder Table No. II is an extension of the upper portion, and
is manipulated in the same manner except that the bottom line of
figures is used for the first weight, and the right side of cylinder
for second weight. Turn the cylinder down instead of up when using it.
Examples (Test Pieces)
MODEL A. Table No. II, Kiln-dried or Air-dried Lumber:
If first weight is 90-1/2 and the second weight is 87, the
cylinder table will show the board from which the test
pieces were taken had a moisture content of 3.8 per cent.
MODEL B. Tables No. II and III, Air-dried (also Green and
Kiln-dried) Lumber.
If the first weight on lower cylinder is 97 and the second
weight is 76, the table will show 21.6 per cent of moisture.
MODEL C. Table III, Green Lumber:
If the first weight is 94 and the second weight is 51, the
table shows 45.8 per cent of moisture.
Keep Records of the Moisture Content
=Saw Mills.=--Should test and mark each pile of lumber when first piled
in the yard, and later when sold it should be again tested and the two
records given to the purchaser.
=Factories.=--Should test and mark the lumber when first received, and
if piled in the yard to be kiln-dried later, it should be tested
before going into the dry kiln, and again before being removed, and
these records placed on file for future reference.
Kiln-dried lumber piled in storage rooms (without any heat) will
absorb 7 to 9 per cent of moisture, and even when so stored should be
tested for moisture before being manufactured into the finished
product.
Never work lumber through the factory that has more than 5 or 6 per
cent of moisture or less than 3 per cent.
Dry storage rooms should be provided with heating coils and properly
ventilated.
Oak or any other species of wood that shows 25 or 30 per cent of
moisture when going into the dry kiln, will take longer to dry than it
would if it contained 15 to 20 per cent, therefore the importance of
testing before putting into the kiln as well as when taking it out.
The Electric Heater
In Figure 101 is shown the Electric Heater. This heater is especially
designed to dry quickly the test pieces for use in connection with the
Scalometer (see Fig. 100) without charring them. It may be attached to
any electric light socket of 110 volts direct or alternating current.
A metal rack is provided to hold the test pieces vertically on edge.
[Illustration: Fig. 101. The Electric Heater.]
Turn the test pieces over once or twice while drying.
It will require from 20 minutes to one hour to remove all the moisture
from the test pieces when placed on this heater, depending on whether
they are cut from green, air-dried, or kiln-dried boards.
Test pieces cut from softwoods will dry quicker than those cut from
hardwoods.
When the test pieces fail to show any further loss in weight, they are
then free from all moisture content.
BIBLIOGRAPHY
AMERICAN BLOWER COMPANY, Detroit, Mich.
IMRE, JAMES E., "The Kiln-drying of Gum," The United States
Dept. of Agriculture, Division of Forestry.
NATIONAL DRY KILN COMPANY, Indianapolis, Ind.
PRICHARD, REUBEN P., "The Structure of the Common Woods,"
The United States Dept. of Agriculture, Division of Forestry,
Bulletin No. 3.
ROTH, FILIBERT, "Timber," The United States Dept. of Agriculture,
Division of Forestry, Bulletin No. 10.
STANDARD DRY KILN COMPANY, Indianapolis, Ind.
STURTEVANT COMPANY, B. F., Boston, Mass.
TIEMAN, H. D., "The Effects of Moisture upon the Strength and
Stiffness of Wood," The United States Dept. of Agriculture,
Division of Forestry, Bulletin No. 70.
TIEMAN, H. D., "Principles of Kiln-drying Lumber," The United
States Dept. of Agriculture, Division of Forestry.
TIEMAN, H. D., "The Theory of Drying and its Application, etc.,"
The United States Dept. of Agriculture, Division of Forestry,
Bulletin No. 509.
THE UNITED STATES DEPT. OF AGRICULTURE, DIVISION OF FORESTRY,
"Check List of the Forest Trees of the United States."
THE UNITED STATES DEPT. OF AGRICULTURE, DIVISION OF
FORESTRY, Bulletin No. 37.
VON SCHRENK, HERMAN, "Seasoning of Timbers," The United
States Dept. of Agriculture, Division of Forestry, Bulletin
No. 41.
WAGNER, J. B., "Cooperage," 1910.
GLOSSARY
=Abnormal.= Differing from the usual structure.
=Acuminate.= Tapering at the end.
=Adhesion.= The union of members of different floral whorls.
=Air-seasoning.= The drying of wood in the open air.
=Albumen.= A name applied to the food store laid up outside the
embryo in many seeds; also nitrogenous organic matter found in plants.
=Alburnam.= Sapwood.
=Angiosperms.= Those plants which bear their seeds within a
pericarp.
=Annual rings.= The layers of wood which are added annually to
the tree.
=Apartment kiln.= A drying arrangement of one or more rooms
with openings at each end.
=Arborescent.= A tree in size and habit of growth.
=Baffle plate.= An obstruction to deflect air or other currents.
=Bastard cut.= Tangential cut. Wood of inferior cut.
=Berry.= A fruit whose entire pericarp is succulent.
=Blower kiln.= A drying arrangement in which the air is blown
through heating coils into the drying room.
=Box kiln.= A small square heating room with openings in one end
only.
=Brittleness.= Aptness to break; not tough; fragility.
=Burrow.= A shelter; insect's hole in the wood.
=Calorie.= Unit of heat; amount of heat which raises the
temperature.
=Calyx.= The outer whorl of floral envelopes.
=Capillary.= A tube or vessel extremely fine or minute.
=Case-harden.= A condition in which the pores of the wood are
closed and the outer surface dry, while the inner portion is
still wet or unseasoned.
=Cavity.= A hollow place; a hollow.
=Cell.= One of the minute, elementary structures comprising the
greater part of plant tissue.
=Cellulose.= A primary cell-wall substance.
=Checks.= The small chinks or cracks caused by the rupture of the
wood fibres.
=Cleft.= Opening made by splitting; divided.
=Coarse-grained.= Wood is coarse-grained when the annual rings
are wide or far apart.
=Cohesion.= The union of members of the same floral whorl.
=Contorted.= Twisted together.
=Corolla.= The inner whorl of floral envelopes.
=Cotyledon.= One of the parts of the embryo performing in part the
function of a leaf, but usually serving as a storehouse of food
for the developing plant.
=Crossers.= Narrow wooden strips used to separate the material on
kiln cars.
=Cross-grained.= Wood is cross-grained when its fibres are spiral
or twisted.
=Dapple.= An exaggerated form of mottle.
=Deciduous.= Not persistent; applied to leaves that fall in autumn
and to calyx and corolla when they fall off before the fruit
develops.
=Definite.= Limited or defined.
=Dew-point.= The point at which water is deposited from moisture-laden
air.
=Dicotyledon.= A plant whose embryo has two opposite cotyledons.
=Diffuse.= Widely spreading.
=Disk.= A circular, flat, thin piece or section of the tree.
=Duramen.= Heartwood.
=Embryo.= Applied in botany to the tiny plant within the seed.
=Enchinate.= Beset with prickles.
=Expansion.= An enlargement across the grain or lengthwise of the
wood.
=Fibres.= The thread-like portion of the tissue of wood.
=Fibre-saturation point.= The amount of moisture wood will imbibe,
usually 25 to 30 per cent of its dry-wood weight.
=Figure.= The broad and deep medullary rays as in oak showing
when the timber is cut into boards.
=Filament.= The stalk which supports the anther.
=Fine-grained.= Wood is fine-grained when the annual rings are
close together or narrow.
=Germination.= The sprouting of a seed.
=Girdling.= To make a groove around and through the bark of a
tree, thus killing it.
=Glands.= A secreting surface or structure; a protuberance having
the appearance of such an organ.
=Glaucous.= Covered or whitened with a bloom.
=Grain.= Direction or arrangement of the fibres in wood.
=Grubs.= The larvae of wood-destroying insects.
=Gymnosperms.= Plants bearing naked seeds; without an ovary.
=Habitat.= The geographical range of a plant.
=Heartwood.= The central portion of tree.
=Hollow-horning.= Internal checking.
=Honeycombing.= Internal checking.
=Hot-blast kiln.= A drying arrangement in which the air is blown
through heating coils into the drying room.
=Humidity.= Damp, moist.
=Hygroscopicity.= The property of readily imbibing moisture from
the atmosphere.
=Indefinite.= Applied to petals or other organs when too numerous
to be conveniently counted.
=Indigenous.= Native to the country.
=Involute.= A form of vernation in which the leaf is rolled inward
from its edges.
=Kiln-drying.= Drying or seasoning of wood by artificial heat in an
inclosed room.
=Leaflet.= A single division of a compound leaf.
=Limb.= The spreading portion of the tree.
=Lumen.= Internal space in the spring- and summer-wood fibres.
=Median.= Situated in the middle.
=Medulla.= The pith.
=Medullary rays.= Rays of fundamental tissue which connect the
pith with the bark.
=Membranous.= Thin and rather soft, more or less translucent.
=Midrib.= The central or main rib of a leaf.
=Moist-air kiln.= A drying arrangement in which the heat is taken
from radiating coils located inside the drying room.
=Mottle.= Figure transverse of the fibres, probably caused by the
action of wind upon the tree.
=Non-porous.= Without pores.
=Oblong.= Considerably longer than broad, with flowing outline.
=Obtuse.= Blunt, rounded.
=Oval.= Broadly elliptical.
=Ovary.= The part of the pistil that contains the ovules.
=Parted.= Cleft nearly, but not quite to the base or midrib.
=Parenchyma.= Short cells constituting the pith and pulp of the
tree.
=Pericarp.= The walls of the ripened ovary, the part of the fruit
that encloses the seeds.
=Permeable.= Capable of being penetrated.
=Petal.= One of the leaves of the corolla.
=Pinholes.= Small holes in the wood caused by worms or insects.
=Pistil.= The modified leaf or leaves which bear the ovules; usually
consisting of ovary, style and stigma.
=Plastic.= Elastic, easily bent.
=Pocket kilns.= Small drying rooms with openings on one end only
and in which the material to be dried is piled directly on the
floor.
=Pollen.= The fertilizing powder produced by the anther.
=Pores.= Minute orifices in wood.
=Porous.= Containing pores.
=Preliminary steaming.= Subjecting wood to a steaming process
before drying or seasoning.
=Progressive kiln.= A drying arrangement with openings at both
ends, and in which the material enters at one end and is discharged
at the other.
=Rick.= A pile or stack of lumber.
=Rift.= To split; cleft.
=Ring shake.= A large check or crack in the wood following an
annual ring.
=Roe.= A peculiar figure caused by the contortion of the woody
fibres, and takes a wavy line parallel to them.
=Sapwood.= The outer portions of the tree next to the bark;
alburnam.
=Saturate.= To cause to become completely penetrated or soaked.
=Season checks.= Small openings in the ends of the wood caused
by the process of drying.
=Seasoning.= The process by which wood is dried or seasoned.
=Seedholes.= Minute holes in wood caused by wood-destroying
worms or insects.
=Shake.= A large check or crack in wood caused by the action of
the wind on the tree.
=Shrinkage.= A lessening or contraction of the wood substance.
=Skidways.= Material set on an incline for transporting lumber or
logs.
=Species.= In science, a group of existing things, associated according
to properties.
=Spermatophyta.= Seed-bearing plants.
=Spring-wood.= Wood that is formed in the spring of the year.
=Stamen.= The pollen-bearing organ of the flower, usually consisting
of filament and anther.
=Stigma.= That part of the pistil which receives the pollen.
=Style.= That part of the pistil which connects the ovary with the
stigma.
=Taproot.= The main root or downward continuation of the plant
axis.
=Temporary checks.= Checks or cracks that subsequently close.
=Tissue.= One of the elementary fibres composing wood.
=Thunder shake.= A rupture of the fibres of the tree across the
grain, which in some woods does not always break them.
=Tornado shake.= (See Thunder shake.)
=Tracheids.= The tissues of the tree which consist of vertical cells
or vessels closed at one end.
=Warping.= Turning or twisting out of shape.
=Wind shake.= (See Thunder shake.)
=Working.= The shrinking and swelling occasioned in wood.
=Wormholes.= Small holes in wood caused by wood-destroying
worms.
=Vernation.= The arrangement of the leaves in the bud.
=Whorl.= An arrangement of organs in a circle about a central axis.
INDEX OF LATIN NAMES
Abies amabalis, 21
Abies balsamea, 20
Abies concolor, 20
Abies grandis, 20
Abies magnifica, 21
Abies nobilis, 21
Acer macrophyllum, 69
Acer negundo, 69
Acer Pennsylvanicum, 70
Acer rubrum, 69
Acer saccharinum, 69
Acer saccharum, 68
Acer spicatum, 69
Æsculus flava, 45
Æsculus glabra, 45
Æsculus octandra, 45
Ailanthus glandulosa, 37
Asimina triloba, 76
Betula lenta, 41
Betula lutea, 42
Betula nigra, 43
Betula papyrifera, 43
Betula populifolia, 42
Betula rubra, 43
Buxus sempervirens, 77
Carpinus Caroliana, 44
Castanea Americana, 48
Castanea chrysophylla, 49
Castanea dentata, 48
Castanea pumila, 48
Castanea vesca, 48
Castanea vulgaris, 48
Catalpa bignonioides, 46
Catalpa speciosa, 46
Celtis occidentalis, 62
Chamæcyparis Lawsonia, 18
Chamæcyparis thyoides, 17
Cladrastis lutea, 85
Cornus florida, 49
Cupressus nootkatensis, 18
Diospyros Virginia, 77
Evonymus atropurpureus, 82
Fagus ferruginea, 40
Fraxinus Americana, 37
Fraxinus Caroliniana, 39
Fraxinus nigra, 38
Fraxinus Oregana, 38
Fraxinus Pennsylvanica, 38
Fraxinus pubescens, 38
Fraxinus quadrangulata, 38
Fraxinus sambucifolia, 38
Fraxinus viridis, 38
Gleditschia triacanthos, 66
Gymnocladus dioicus, 49
Hicoria alba, 64
Hicoria glabra, 64
Hicoria minima, 64
Hicoria ovata, 64
Hicoria pecan, 64
Ilex monticolo, 65
Ilex opaca, 64
Juglans cinerea, 45
Juglans nigra, 82
Juniperus communis, 19
Juniperus Virginiana, 18
Larix Americana, 22
Larix laricina, 22
Larix occidentalis, 22
Libocedrus decurrens, 18
Liquidamber styraciflua, 54
Liriodendron tulipfera, 81
Maclura aurantiaca, 76
Magnolia acuminata, 67
Magnolia glauca, 67
Magnolia tripetala, 67
Morus rubra, 70
Nyssa aquatica, 60
Nyssa sylvatica, 62
Ostrya Virginiana, 65
Oxydendrum arboreum, 80
Picea alba, 28
Picea canadensis, 28
Picea engelmanni, 28
Picea mariana, 27
Picea nigra, 27
Picea rubens, 28
Picea sitchensis, 28
Pinus banksiana, 27
Pinus cubensis, 26
Pinus divaricata, 27
Pinus enchinata, 26
Pinus flexilis, 24
Pinus inops, 27
Pinus Jeffreyi, 25
Pinus Lambertiana, 24
Pinus monticolo, 24
Pinus Murryana, 27
Pinus palustris, 24
Pinus ponderosa, 25
Pinus resinosa, 25
Pinus rigida, 26
Pinus strobus, 23
Pinus tæda, 25
Pinus Virginiana, 27
Platanus occidentalis, 80
Platanus racemosa, 81
Populus alba, 79
Populus angulata, 77
Populus balsamifera, 79
Populus fremontii, 78
Populus grandidentata, 79
Populus heteropylla, 78
Populus monilifera, 77
Populus nigra italica, 79
Populus tremuloides, 79
Populus trichocarpa, 78
Populus Wislizeni, 78
Prunus Pennsylvanica, 47
Prunus serotina, 47
Pseudotsuga douglasii, 29
Pseudotsuga taxifolia, 29
Pyrus coronaria, 49
Quercus acuminata, 73
Quercus alba, 71
Quercus aquatica, 73
Quercus bicolor, 72
Quercus chrysolepis, 76
Quercus coccinea, 75
Quercus digitata, 75
Quercus durandii, 71
Quercus falcata, 75
Quercus garryana, 71
Quercus ilicijolia, 74
Quercus imbricaria, 75
Quercus lobata, 72
Quercus lyrata, 73
Quercus macrocarpa, 72
Quercus marilandica, 75
Quercus Michauxii, 74
Quercus minor, 74
Quercus nigra, 75
Quercus obtusiloda, 74
Quercus palustris, 73
Quercus phellos, 72
Quercus platanoides, 72
Quercus prinoides, 74
Quercus prinus, 73
Quercus pumila, 74
Quercus rubra, 74
Quercus tinctoria, 74
Quercus velutina, 74
Quercus virens, 75
Rhamnus Caroliniana, 45
Robinia pseudacacia, 66
Robinia viscosa, 66
Salix alba, 83
Salix amygdaloides, 84
Salix babylonica, 84
Salix bebbiana, 84
Salix discolor, 84
Salix fluviatilis, 84
Salix fragilis, 84
Salix lucida, 84
Salix nigra, 83
Salix rostrata, 84
Salix vitellina, 83
Sassafras sassafras, 80
Sequoia sempervirens, 19
Taxodium distinchum, 19
Taxus brevifolia, 30
Thuya gigantea, 17
Thuya occidentalis, 17
Tilia Americana, 39
Tilia heterophylla, 39
Tilia pubescens, 39
Tsuga canadensis, 21
Tsuga mertensiana, 21
Ulmus alata, 51
Ulmus Americana, 50
Ulmus crassifolia, 51
Ulmus fulva, 51
Ulmus pubescens, 51
Ulmus racemosa, 50
Umbellularia Californica, 65
INDEX
Abele, Tree, 79
Absorption of water by dry wood, 124
Acacia, 66
Acacia, false, 66
Acacia, three-thorned, 66
According to species, different kiln drying, 170
Advantages in seasoning, 128
Advantages of kiln-drying over air-drying, 156
Affect drying, properties of wood that, 156
Ailanthus, 37
Air circulation, 173
Air-drying, advantages of kiln-drying over, 156
Alaska cedar, 18
Alaska cypress, 18
Alcoholic liquids, stave and heads of barrels containing, 112
Almond-leaf willow, 84
Ambrosia or timber beetles, 99
American box, 49
American elm, 50
American larch, 22
American linden, 39
American oak, 71
American red pine, 25
Anatomical structure, 14
Annual ring, the yearly or, 10
Apartment dry kiln, 198
Apple, crab, 49
Apple, custard, 76
Apple, wild, 49
Appliances in kiln-drying, helpful, 237
Arborvitæ, 17
Ash, 37
Ash, black, 38
Ash, blue, 38
Ash, Carolina, 39
Ash, green, 38
Ash, ground, 38
Ash, hoop, 38
Ash-leaved maple, 69
Ash, Oregon, 38
Ash, red, 38
Ash, white, 37
Aspen, 39, 79
Aspen, large-toothed, 78
Aspen-leaved birch, 42
Aspen, quaking, 79
Atmospheric pressure, drying at, 146
Bald Cypress, 19
Ball tree, button, 80
Balm of gilead, 79
Balm of gilead fir, 20
Balsam, 20, 79
Balsam fir, 20
Bark and pith, 8
Bark on, round timber with, 106
Barrels containing alcoholic liquids, staves and heads of, 112
Barren oak, 75
Bar willow, sand, 84
Basket oak, 74
Basswood, 39
Basswood, small-leaved, 39
Basswood, white, 39
Bastard pine, 26
Bastard spruce, 29
Bay poplar, 60
Bay, sweet, 67
Bear oak, 74
Beaver wood, 67
Bebb willow, 84
Bee tree, 39
Beech, 40
Beech, blue, 44
Beech, red, 40
Beech, water, 44, 80
Beech, white, 40
Berry, sugar, 62
Beetles, ambrosia or timber, 99
Big bud hickory, 64
Bilsted, 54
Birch, 41
Birch, aspen-leaved, 42
Birch, black, 41
Birch, canoe, 43
Birch, cherry, 41
Birch, gray, 42
Birch, mahogany, 41
Birch, old field, 42
Birch, paper, 43
Birch, red, 42
Birch, river, 43
Birch, silver, 42
Birch, sweet, 41
Birch, white, 42, 43
Birch, wintergreen, 41
Birch, yellow, 42
Bird cherry, 47
Bitternut hickory, 64
Black ash, 38
Black birch, 41
Black cherry, 47
Black cottonwood, 78
Black cypress, 19
Black gum, 62
Black hickory, 64
Black jack, 75
Black larch, 22
Black locust, 66
Black nut hickory, 64
Black oak, 74
Black pine, 25, 27
Black spruce, 27
Black walnut, 44, 82
Black willow, 83
Blower dry kiln, operation of, 186
Blower or hot blast dry kiln, 185
Blue ash, 38
Blue beech, 44
Blue poplar, 81
Blue willow, 83
Bois d'Arc, 45, 76
Bolts, stave, heading and shingle, 109
Borers, flat-headed, 103
Borers, powder post, 105
Borers, round-headed, 101
Box, American, 49
Box elder, 69
Box dry kiln, 204
Broad-leaved maple, 69
Broad-leaved trees, 31
Broad-leaved trees, list of most important, 37
Broad-leaved trees, wood of, 31
Brown hickory, 64
Brown locust, 66
Buckeye, 45
Buckeye, fetid, 45
Buckeye, Ohio, 45
Buckeye, sweet, 45
Buckthorne, 45
Bud hickory, big, 64
Bull nut hickory, 64
Bull pine, 25
Bur oak, 72
Burning bush, 82
Bush, burning, 82
Bush, juniper, 18
Butternut, 45
Button ball tree, 80
Button wood, 80
California Redwood, 19
California white pine, 25
Canadian pine, 25
Canary wood, 81
Canoe birch, 43
Canoe cedar, 17
Carolina ash, 39
Carolina pine, 26
Carolina poplar, 77
Cars, method of loading kiln, 206
Catalpa, 46
Cedar, 17
Cedar, Alaska, 18
Cedar, canoe, 17
Cedar, elm, 51
Cedar, ground, 19
Cedar, incense, 18
Cedar of the West, red, 17
Cedar, Oregon, 18
Cedar, pencil, 18
Cedar, Port Orford, 18
Cedar, red, 18, 19
Cedar, white, 17, 18
Cedar, yellow, 18
Changes rendering drying difficult, 140
Characteristics and properties of wood, 1
Checking and splitting, prevention of, 129
Cherry, 47
Cherry birch, 41
Cherry, bird, 47
Cherry, black, 47
Cherry, Indian, 45
Cherry, red, 47
Cherry, rum, 47
Cherry, wild, 47
Cherry, wild red, 47
Chestnut, 48
Chestnut, horse, 45, 65
Chestnut oak, 73
Chestnut oak, rock, 73
Chestnut oak, scrub, 74
Chinquapin, 48, 49
Chinquapin oak, 73, 74
Chinquapin oak, dwarf, 74
Choice of drying method, 195
Circassian walnut, 60
Circulation, air, 173
Clammy locust, 66
Classes of trees, 5
Cliff elm, 50
Coast redwood, 19
Coffee nut, 49
Coffee tree, 49
Color and odor of wood, 89
Color, odor, weight, and figure in wood, grain, 86
Composition of sap, 116
Conditions and species, temperature depends on, 171
Conditions favorable for insect injury, 106
Conditions governing the drying of wood, 156
Conditions of success in kiln-drying, 169
Coniferous trees, 8
Coniferous trees, wood of, 8
Coniferous woods, list of important, 17
Containing alcoholic liquids, staves and heads of barrels, 112
Cooperage stock and wooden truss hoops, dry, 112
Cork elm, 50
Cotton gum, 60
Cottonwood, 49, 77, 78
Cottonwood, black, 78
Cottonwood, swamp, 78
Cow oak, 74
Crab apple, 49
Crab, fragrant, 49
Crack willow, 84
Crude products, 106
Cuban pine, 26
Cucumber tree, 49, 67
Cup oak, mossy, 72
Cup oak, over-, 72, 73
Custard apple, 76
Cypress, 19
Cypress, Alaska, 18
Cypress, bald, 19
Cypress, black, 19
Cypress, Lawson's, 18
Cypress, pecky, 19
Cypress, red, 19
Cypress, white, 19
D'Arc, Bois, 45, 76
Deal, yellow, 23
Demands upon soil and moisture of red gum, 56
Depends on conditions and species, temperature, 171
Description of the forest service kiln, theory and, 161
Diagram, the uses of the humidity, 237
Difference between seasoned and unseasoned wood, 121
Different grains of wood, 86
Different kiln-drying according to species, 170
Different species, weight of kiln-dried wood of, 95
Different types, kilns of, 196
Different types of dry kilns, 185
Different types of kiln doors, 231
Difficult, changes rendering drying, 140
Difficulties of drying wood, 138
Distribution of water in wood, 114
Distribution of water in wood, local, 114
Distribution of water in wood seasonal, 115
Dogwood, 49
Doors, different types of kiln, 231
Douglas spruce, 29
Downy linden, 39
Downy poplar, 78
Dry cooperage stock and wooden truss hoops, 112
Drying according to species, different kiln, 170
Drying, advantages of kiln-drying over air, 156
Drying at atmospheric pressure, 146
Drying by superheated steam, 150
Drying, conditions of success in kiln, 169
Drying difficult, changes rendering, 140
Drying gum, kiln, 180
Drying, helpful appliances in kiln, 237
Drying, kiln, 164, 177
Drying, losses due to improper kiln, 141
Drying method, choice of, 185
Drying, methods of kiln, 145
Drying, objects of kiln, 168
Drying of green red gum, kiln, 183
Drying of wood, kiln, 156
Drying of wood, physical conditions governing the, 156
Drying, physical properties that influence, 125
Drying, properties of wood that effect, 141
Drying, theory of kiln, 157
Drying, underlying principles of kiln, 166
Drying under pressure and vacuum, 146
Drying, unsolved problems in kiln, 143
Drying wood, difficulties of, 138
Drying 100 lb. of green wood in the kiln, pounds of water lost, 179
Dry kiln, apartment, 198
Dry kiln, box, 204
Dry kiln, operation of the blower, 186
Dry kiln, operation of the moist-air, 192
Dry kiln, moist-air or pipe, 188
Dry kiln, pocket, 200
Dry kiln, progressive, 196
Dry kiln, requirements in a satisfactory, 160
Dry kilns, different types of, 185
Dry kiln specialties, 206
Dry kilns, types of, 185
Dry kiln, tower, 202
Dry wood, absorption of water by, 124
Duck oak, 73
Due to improper kiln-drying, losses, 141
Dwarf chinquapin oak, 74
Effects of Moisture on Wood, 117
Elder, box, 69
Electric heater, the, 250
Elimination of stain and mildew, 136
Elm, 50
Elm, American, 50
Elm, cedar, 51
Elm, cliff, 50
Elm, cork, 50
Elm, hickory, 50
Elm, moose, 51
Elm, red, 51
Elm, rock, 50
Elm, slippery, 51
Elm, water, 50
Elm, winged, 51
Elm, white, 50
Enemies of wood, 98
Evaporation of water, manner of, 123
Evaporation, rapidity of, 124
Expansion of wood, 135
Factories, Scalometer in, 249
False acacia, 66
Favorable for insect injury, conditions, 106
Fetid buckeye, 45
Fibre saturation point in wood, 118
Field birch, old, 42
Field pine, old, 25, 26
Figure in wood, 96
Figure in wood, grain, color, odor, weight, and, 86
Final steaming of gum, 182
Fir, 20
Fir, balm of gilead, 20
Fir balsam, 20
Fir, noble, 21
Fir, red, 21, 29
Fir tree, 20
Fir, white, 20, 21
Fir, yellow, 29
Flat-headed borers, 103
Forest service kiln, theory and description of, 161
Form of the red gum, 55
Fragrant crab, 49
Gauge, the Recording Steam, 246
Georgia pine, 24
Gilead, balm of, 79
Gilead fir, balm of, 20
Ginger pine, 18
Glaucous willow, 84
Governing the drying of wood, physical conditions, 156
Grain, color, odor, weight, and figure in wood, 86
Grains of wood, different, 86
Gray birch, 42
Gray pine, 27
Green ash, 38
Green red gum, kiln-drying, 183
Green wood in the kiln, pounds of water lost in drying 100 lbs., 179
Ground ash, 38
Ground cedar, 19
Growth red gum, second, 59
Gum, 52
Gum, black, 62
Gum, cotton, 60
Gum, demands upon soil and moisture of red, 56
Gum, final steaming of, 182
Gum, form of red, 55
Gum, kiln-drying, 180
Gum, kiln-drying of green red, 183
Gum, method of piling, 180
Gum, preliminary steaming of, 182
Gum, range of red, 55
Gum, range of tupelo, 61
Gum, red, 54, 79
Gum, reproduction of red, 57
Gum, second-growth red, 59
Gum, sour, 62, 80
Gum, sweet, 54, 80
Gum, tolerance of the red, 56
Gum, tupelo, 60
Gum, uses of tupelo, 61
Hackberry, 62
Hacmatac, 22
Hard maple, 68
Hard pine, 26
Hard pines, 24
Hard pine, southern, 24
Hardwoods, 37
Hazel pine, 54, 60
Headed borers, flat, 103
Headed borers, round, 101
Heading, stave and shingle bolts, 109
Heads and staves of barrels containing alcoholic liquids, 112
Heart hickory, white, 64
Heartwood, sap and, 8
Heater, the electric, 250
Helpful appliances in kiln-drying, 237
Hemlock, 21
Hemlock spruce, 21
Hickory, 63
Hickory, big bud, 64
Hickory, bitternut, 64
Hickory, black, 64
Hickory, black nut, 64
Hickory, brown, 64
Hickory, bull nut, 64
Hickory elm, 50
Hickory, mockernut, 64
Hickory, pignut, 64
Hickory, poplar, 81
Hickory, scalybark, 64
Hickory, shagbark, 64
Hickory, shellbark, 64
Hickory, swamp, 64
Hickory, switchbud, 64
Hickory, white heart, 64
Holly, 64, 65
Holly, mountain, 65
Honey locust, 66
Honey shucks, 66
Hoop ash, 38
Hoops, dry cooperage stock and wooden truss, 112
Hop hornbeam, 65
Hornbeam, 44
Hornbeam, hop, 65
Horse chestnut, 45, 65
Hot blast or blower kiln, 185
Humidity, 174
Humidity diagram, uses of the, 237
How to prevent insect injury, 107
How wood is seasoned, 145
Hygrodeik, the, 242
Hygrometer, the recording, 242
Hygrometer, the registering, 244
Illinois Nut, 64
Important broad-leaved trees, list of most, 37
Important coniferous woods, list of, 17
Impregnation methods, 151
Improper kiln-drying, losses due to, 141
Incense cedar, 18
Indian bean, 46
Indian cherry, 45
Influence drying, physical properties that, 125
Injury, conditions favorable for insect, 106
Injury from insects, how to prevent, 107
Insect injury, conditions favorable for, 106
Insects, how to prevent injury from, 107
Iron oak, 74
Ironwood, 44, 65
Jack, Black, 75
Jack oak, 75
Jack pine, 27
Jersey pine, 27
Juniper, 18
Juniper bush, 18
Juniper, red, 18
Juniper, savin, 18
Keep Records of the Moisture Content, 249
Kiln, apartment dry, 198
Kiln, blower or hot blast, 185
Kiln, box dry, 204
Kiln cars and method of loading, 206
Kiln doors, different types, 231
Kiln-dried wood of different species, weight of, 95
Kiln-drying, 164, 177
Kiln-drying according to species, different, 170
Kiln-drying, conditions of success in, 169
Kiln-drying gum, 180
Kiln-drying, helpful appliances in, 237
Kiln-drying, losses due to improper, 141
Kiln-drying, objects of, 168
Kiln-drying of green red gum, 183
Kiln-drying of wood, 156
Kiln-drying of wood, 156
Kiln-drying over air-drying, advantages of, 156
Kiln-drying, theory of, 157
Kiln-drying, underlying principles of, 166
Kiln-drying, unsolved problems in, 143
Kiln, operation of the blower dry, 186
Kiln, operation of the moist-air dry, 192
Kiln, pipe or moist-air dry, 188
Kiln, pocket dry, 200
Kiln, progressive dry, 196
Kiln, requirements in a satisfactory dry, 160
Kilns, different types of dry, 185
Kilns of different types, 196
Kiln specialties, dry, 206
Kiln, theory and description of the forest service, 161
Kilns, types of dry, 185
Kiln, tower dry, 202
Land Spruce, Tide, 28
Larch, 22
Larch, American, 22
Larch, black, 22
Larch, western, 22
Large-toothed aspen, 79
Laurel, 65
Laurel oak, 75
Lawson's cypress, 18
Leaf pine, long-, 24
Leaf pine, short-, 26
Leaf willow, long, 84
Leaved basswood, small, 39
Leaved birch, aspen, 42
Leaved maple, ash, 69
Leaved maple, broad, 69
Leaved maple, silver, 69
Leaved trees, broad, 31
Leaved trees, list of most important broad, 37
Leaved trees, wood of broad, 31
Leverwood, 65
Life, tree of, 17
Lime tree, 39
Lin, 39
Linden, 39
Linden, American, 39
Linden, downy, 39
Liquidamber, 54
Liquids, staves and heads of barrels containing alcoholic, 112
List of important coniferous trees, 17
List of most important broad-leaved trees, 37
Live oak, 75, 76
Loading, kiln cars and method of, 206
Loblolly pine, 25
Local distribution of water in wood, 114
Locust, 66
Locust, black, 66
Locust, brown, 66
Locust, clammy, 66
Locust, honey, 66
Locust, sweet, 66
Locust, yellow, 66
Lodge-pole pine, 27
Lombardy poplar, 79
Long-leaf pine, 24
Long-leaf willow, 84
Long-straw pine, 24
Losses due to improper kiln-drying, 141
Lost in kiln-drying 100 lb. green wood in the kiln, pounds of water, 179
Magnolia, 67
Magnolia, small, 67
Magnolia, swamp, 67
Mahogany, birch, 41
Mahogany, white, 45
Manner of evaporation of water, 123
Maple, 67
Maple, ash-leaved, 69
Maple, broad-leaved, 69
Maple, hard, 68
Maple, mountain, 69
Maple, Oregon, 69
Maple, red, 69
Maple, rock, 68
Maple, silver, 69
Maple, silver-leaved, 69
Maple, soft, 69
Maple, striped, 70
Maple, sugar, 68
Maple, swamp, 69
Maple, water, 69
Maple, white, 69
Maul oak, 75, 76
Meadow pine, 26
Method, choice of drying, 195
Method of loading kiln cars, 206
Method of piling gum, 180
Methods, impregnation, 151
Methods of drying, 154
Mildew, elimination of stain and, 136
Minute structure, 34
Mockernut hickory, 64
Moist-air dry kiln, operation of, 192
Moist-air or pipe kiln, the, 188
Moisture content, keep records of the, 249
Moisture, demands upon soil and, 56
Moisture on wood, effects of, 117
Moose elm, 51
Moose-wood, 70
Mossy-cup oak, 72
Most important broad-leaved trees list of, 37
Mountain holly, 65
Mountain maple, 69
Mulberry, 70
Mulberry, red, 70
Myrtle, 65, 70
Nettle Tree, 62
Noble fir, 21
Norway pine, 25
Nut, coffee, 49
Nut hickory, black, 64
Nut hickory, bull, 64
Nut, Illinois, 64
Nyssa, 60
Oak, 70
Oak, American, 71
Oak, barren, 75
Oak, basket, 74
Oak, bear, 74
Oak, black, 74
Oak, bur, 72
Oak, chestnut, 73
Oak, chinquapin, 73, 74
Oak, cow, 74
Oak, duck, 73
Oak, dwarf chinquapin, 74
Oak, iron, 74
Oak, jack, 75
Oak, laurel, 75
Oak, live, 75, 76
Oak, maul, 75, 76
Oak, mossy-cup, 72
Oak, over-cup, 72, 73
Oak, peach, 72
Oak, pin, 73
Oak, possum, 73
Oak, post, 74
Oak, punk, 73
Oak, red, 74, 75
Oak, rock, 73
Oak, rock chestnut, 73
Oak, scarlet, 75
Oak, scrub, 74
Oak, scrub chestnut, 74
Oak, shingle, 75
Oak, Spanish, 75
Oak, swamp post, 73
Oak, swamp Spanish, 73
Oak, swamp white, 72, 73
Oak, water, 73
Oak, western white, 71
Oak, white, 71, 72
Oak, willow, 72
Oak, yellow, 73, 74
Oak, Valparaiso, 76
Objects of kiln-drying, 168
Odor and color of wood, 89
Odor, weight, and figure in wood, grain, color, 86
Ohio buckeye, 45
Old field birch, 42
Old field pine, 25, 26
Operation of the blower kiln, 186
Operation of the moist-air kiln, 192
Orange, osage, 76
Oregon ash, 38
Oregon cedar, 18
Oregon maple, 69
Oregon pine, 29
Orford cedar, Port, 18
Osage orange, 76
Out-of-door seasoning, 154
Over-cup oak, 72, 73
Papaw, 76
Paper birch, 43
Peach oak, 72
Pecan, 64
Pecky cypress, 19
Pencil cedar, 18
Pepperidge, 60
Perch willow, 84
Persimmon, 77
Peruche, 21
Physical conditions governing the drying of wood, 156
Physical properties that influence drying, 125
Pignut hickory, 64
Piling gum, methods of, 180
Pine, American red, 25
Pine, bastard, 26
Pine, black, 25, 27
Pine, bull, 25
Pine, California white, 25
Pine, Canadian, 25
Pine, Carolina, 26
Pine, Cuban, 26
Pine, Georgia, 24
Pine, ginger, 18
Pine, gray, 27
Pine, hard, 26
Pine, hazel, 54, 60
Pine, jack, 27
Pine, Jersey, 27
Pine, loblolly, 25
Pine, lodge-pole, 27
Pine, long-leaf, 24
Pine, long-straw, 24
Pine, meadow, 26
Pine, Norway, 25
Pine, old field, 25, 26
Pine, Oregon, 29
Pine, pitch, 26
Pine, Puget Sound, 29
Pine, pumpkin, 23, 24
Pine, red, 29
Pine, rosemary, 25
Pine, sap, 25
Pine, scrub, 27
Pines, hard, 24
Pine, short-leaf, 26
Pine, short-straw, 25
Pine, slash, 25, 26
Pine, soft, 23, 24
Pine, southern, 24
Pine, southern hard, 24
Pine, spruce, 26
Pine, sugar, 24
Pine, swamp, 26
Pine, torch, 26
Pine, Weymouth, 23
Pine, western, 25
Pine, western white, 25
Pine, western yellow, 25
Pine, white, 23, 24
Pine, yellow, 24, 25, 26
Pin oak, 73
Pipe or moist-air kiln, 188
Pitch pine, 26
Pith and bark, 8
Plane tree, 80
Pocket dry kiln, the, 200
Point in wood, the fibre saturation, 118
Pole pine, lodge, 27
Poplar, 67, 77, 79, 81
Poplar, bay, 60
Poplar, blue, 81
Poplar, Carolina, 77
Poplar, downy, 78
Poplar, hickory, 81
Poplar, Lombardy, 79
Poplar, swamp, 60
Poplar, white, 79, 81
Poplar, yellow, 81
Port Orford cedar, 18
Possum oak, 73
Post borers, powder, 105
Post oak, 74
Post oak, swamp, 73
Pounds of water lost in drying 100 lb. green wood in the kiln, 179
Powder post borers, 105
Preliminary steaming of gum, 182
Preliminary treatments, 151
Pressure and vacuum, drying under, 146
Pressure, drying at atmospheric, 146
Prevent injury from insects, how to, 107
Prevention of checking and splitting, 129
Principles of kiln-drying, underlying, 166
Problems in kiln-drying, unsolved, 143
Products, crude, 106
Products in the rough, seasoned, 112
Products in the rough, unseasoned, 109
Progressive dry kiln, the, 196
Properties, characteristics and, 1
Properties of wood, 4
Properties of wood that affect drying, 141
Properties that influence drying, physical, 125
Puget Sound pine, 29
Pumpkin pine, 23, 24
Punk oak, 73
Pussy willow, 84
Quaking Aspen, 79
Range of Red Gum, 55
Range of tupelo gum, 61
Rapidity of evaporation, 124
Recording hygrometer, the, 242
Recording steam gauge, the, 246
Recording thermometer, the, 245
Records of the moisture content, keep, 249
Red ash, 38
Red beech, 40
Red birch, 43
Red cedar, 18, 19
Red cedar of the West, 17
Red cherry, 47
Red cherry, wild, 47
Red cypress, 19
Red elm, 51
Red fir, 21, 29
Red gum, 54, 79
Red gum, demands upon soil and moisture of, 56
Red gum, form of the, 55
Red gum, kiln-drying of green, 183
Red gum, range of, 55
Red gum, reproduction of, 57
Red gum, second-growth, 59
Red gum, tolerance of, 56
Red juniper, 18
Red maple, 69
Red mulberry, 70
Red oak, 74, 75
Red pine, 29
Red pine, American, 25
Red spruce, 28
Redwood, 19, 27
Redwood, California, 19
Redwood, Coast, 19
Registering hygrometer, the, 244
Registering thermometer, the, 246
Rendering drying difficult, changes, 140
Reproduction of red gum, 57
Requirements in a satisfactory dry kiln, 160
Ring, the annual or yearly, 10
River birch, 43
Rock chestnut oak, 73
Rock elm, 50
Rock maple, 68
Rock oak, 73
Rosemary pine, 25
Rough, seasoned products in the, 112
Rough, unseasoned products in the, 109
Round-headed borers, 101
Round timber with bark on, 106
Rum cherry, 47
Samples for Scalometer Test, 248
Sand bar willow, 84
Sap and heartwood, 8
Sap, composition of, 116
Saplings, 108
Sap pine, 25
Sassafras, 80
Satin walnut, 54
Satisfactory dry kiln, requirements in a, 160
Saturation point in wood, fibre, 118
Sawmills, scalometer in, 249
Savin juniper, 18
Scalometer in factories, 249
Scalometer in sawmills, 249
Scalometer, test samples for, 248
Scalometer, the troemroid, 247
Scalometer, weighing with, 248
Scalybark hickory, 64
Scarlet oak, 75
Scrub chestnut oak, 74
Scrub oak, 74
Scrub pine, 27
Seasonal distribution of water in wood, 115
Seasoned and unseasoned wood, difference between, 121
Seasoned, how wood is, 145
Seasoned products in the rough, 112
Seasoning, advantages in, 128
Seasoning is, what, 119
Seasoning, out-of-door, 154
Second-growth red gum, 59
Sequoia, 19
Service kiln, theory and description of forest, 161
Shagbark hickory, 64
Shellbark hickory, 64
Shingle, heading and stave bolts, 109
Shingle oak, 75
Shining willow, 84
Short-leaf pine, 26
Short-straw pine, 25
Shrinkage of wood, 130
Shucks, honey, 66
Sitka spruce, 28
Silver birch, 42
Silver-leaved maple, 69
Silver maple, 69
Slash pine, 25, 26
Slippery elm, 51
Small-leaved basswood, 39
Small magnolia, 67
Soft maple, 69
Soft pine, 23, 24
Soil and moisture, demands upon, 56
Sorrel-tree, 80
Sound pine, Puget, 29
Sour gum, 62, 80
Sourwood, 80
Southern hard pine, 24
Southern pine, 24
Spanish oak, 75
Spanish oak, swamp, 73
Specialties, dry-kiln, 206
Species, different kiln-drying according to, 170
Species, temperature depends upon condition and, 171
Species, weight of kiln-dried wood of different, 95
Spindle tree, 82
Splitting, prevention of checking and, 129
Spring and summer-wood, 12
Spruce, 27
Spruce, bastard, 29
Spruce, black, 27
Spruce, Douglas, 29
Spruce, hemlock, 21
Spruce pine, 26
Spruce, red, 28
Spruce, Sitka, 28
Spruce, tide-land, 28
Spruce, white, 28
Stain and mildew, elimination of, 136
Stave, heading and shingle bolts, 109
Staves and heads of barrels containing alcoholic liquids, 112
Steam, drying by superheated, 150
Steam gauge, the recording, 246
Steaming of gum, preliminary, 182
Steaming of gum, final, 182
Stock and wooden truss hoops, dry cooperage, 112
Straw pine, long, 24
Straw pine, short, 25
Striped maple, 70
Structure, anatomical, 14
Structure, minute, 34
Structure of wood, 4
Stump tree, 49
Success in kiln-drying, conditions of, 169
Sugar berry, 62
Sugar maple, 68
Sugar pine, 24
Summerwood, spring and, 12
Superheated steam, drying by, 150
Swamp cottonwood, 78
Swamp hickory, 64
Swamp magnolia, 67
Swamp maple, 69
Swamp pine, 26
Swamp poplar, 60
Swamp post oak, 73
Swamp Spanish oak, 73
Swamp white oak, 72, 73
Sweet bay, 67
Sweet buckeye, 45
Sweet birch, 41
Sweet gum, 54, 80
Sweet locust, 66
Switchbud hickory, 64
Sycamore, 80, 81
Tacmahac, 79
Tamarack, 22, 27, 29
Temperature depends upon conditions and species, 171
Test samples for scalometer, 248
Theory and description of the forest service kiln, 161
Theory of kiln-drying, 157
Thermometer, the recording, 245
Thermometer, the registering, 246
Thorned acacia, three, 66
Three-thorned acacia, 66
Tide-land spruce, 28
Timber, 1
Timber beetles, ambrosia or, 99
Timber with bark on, round, 106
Timber worms, 103
Tolerance of red gum, 56
Toothed aspen, large-, 79
Torch pine, 26
Tower dry kiln, the, 202
Treatments, preliminary, 151
Tree, abele, 79
Tree, bee, 39
Tree, button ball, 80
Tree, coffee, 49
Tree, cucumber, 49, 67
Tree, fir, 20
Tree, lime, 39
Tree, nettle, 62
Tree of life, 17
Tree, plane, 80
Trees, broad-leaved, 31
Trees, classes of, 5
Trees, coniferous, 8
Trees, list of important coniferous, 17
Trees, list of most important broad-leaved, 37
Tree, sorrel, 80
Tree, spindle, 82
Tree, stump, 49
Trees, wood of broad-leaved, 31
Trees, wood of the coniferous, 8
Tree, tulip, 81
Tree, umbrella, 67
Troemroid Scalometer, the, 247
Truss hoops, dry cooperage stock and, 112
Tulip tree, 81
Tulip wood, 67, 81
Tupelo, 82
Tupelo gum, 60
Tupelo gum, range of, 61
Tupelo gum, uses of, 61
Types of dry kilns, different, 185
Types of kiln doors, different, 231
Types, kilns of different, 196
Umbrella Tree, 67
Underlying principles of kiln-drying, 166
Unseasoned products in the rough, 109
Unseasoned wood, difference between seasoned and, 121
Unsolved problems in kiln-drying, 143
Uses of the humidity diagram, 237
Uses of tupelo gum, 61
Vacuum, Drying under Pressure and, 146
Valparaiso oak, 76
Virgilia, 85
Wahoo, 51, 82
Walnut, 45, 82
Walnut, black, 44, 82
Walnut, circassian, 60
Walnut, satin, 54
Walnut, white, 45, 83
Water beech, 44, 80
Water by dry wood, absorption of, 124
Water elm, 50
Water in wood, 114
Water in wood, distribution of, 114
Water in wood, local distribution of, 114
Water in wood, seasonal distribution of, 115
Water lost in drying 100 lb. of green wood in the kiln, pounds of, 179
Water, manner of evaporation of, 123
Water maple, 69
Water oak, 73
Weeping willow, 84
Weighing with scalometer, 248
Weight, and figure in wood, grain, color, odor, 86
Weight of kiln-dried wood of different species, 95
Weight of wood, 91
Western larch, 22
Western pine, 25
Western white oak, 71
Western white pine, 25
Western yellow pine, 25
West, red cedar of the, 17
Weymouth pine, 23
What seasoning is, 119
White ash, 37
White basswood, 39
White beech, 40
White birch, 42, 43
White cedar, 17, 18
White cypress, 19
White elm, 50
White fir, 20, 21
White heart hickory, 64
White mahogany, 45
White maple, 69
White oak, 71, 72
White oak, swamp, 72, 73
White oak, western, 71
White pine, 23, 24
White pine, California, 25
White pine, western, 25
White poplar, 79, 81
White spruce, 28
White walnut, 45, 83
White willow, 83
Whitewood, 39, 81, 83
Wild apple, 49
Wild cherry, 47
Wild red cherry, 47
Willow, 83
Willow, almond-leaf, 84
Willow, bebb, 84
Willow, black, 83
Willow, blue, 83
Willow, crack, 84
Willow, glaucous, 84
Willow, long-leaf, 84
Willow, oak, 72
Willow, perch, 84
Willow, pussy, 84
Willow, sand bar, 84
Willow, shining, 84
Willow, weeping, 84
Willow, white, 83
Willow, yellow, 83
Winged elm, 51
Wintergreen birch, 41
Wood, absorption of water by dry, 124
Wood, beaver, 67
Wood, canary, 81
Wood, characteristics and properties of, 1
Wood, color and odor of, 89
Wood, different grains of, 86
Wood, difference between seasoned and unseasoned, 121
Wood, difficulties of drying, 138
Wood, distribution of water in, 114
Wood, effects of moisture on, 117
Wood, enemies of, 98
Wood, expansion of, 135
Wood, figure in, 96
Wood, grain, color, odor, weight, and figure in, 86
Wood, how seasoned, 145
Wood in the kiln, pounds of water lost in drying 100 lb. of green, 179
Wood, iron, 65
Wood, kiln-drying of, 156
Wood, lever, 65
Wood, local distribution of water in, 114
Wood, moose, 70
Wood, of broad-leaves trees, 31
Wood of different species, weight of kiln-dried, 95
Wood of coniferous trees, 8
Wood, physical conditions governing the drying of, 156
Wood, properties of, 4
Wood, seasonal distribution of water in, 115
Wood, shrinkage of, 130
Woods, list of important coniferous, 17
Wood, spring and summer, 12
Wood, structure of, 4
Wood that effect drying, properties of, 141
Wood, the fibre saturation point in, 118
Wood, tulip, 67, 81
Wood, water in, 114
Wood, weight of, 89
Wood, white, 81, 83
Wood, yellow, 85
Wooden truss hoops, dry cooperage, stock and, 112
Worms, timber, 103
Yearly Ring, the Annual of, 10
Yellow birch, 42
Yellow cedar, 18
Yellow deal, 23
Yellow fir, 29
Yellow locust, 66
Yellow oak, 73, 74
Yellow pine, 24, 25, 26
Yellow pine, western, 25
Yellow poplar, 81
Yellow willow, 83
Yellow wood, 85
Yew, 29, 30
D. VAN NOSTRAND COMPANY
25 PARK PLACE
NEW YORK
SHORT-TITLE CATALOG
OF
Publications and Importations
OF
SCIENTIFIC AND ENGINEERING
BOOKS
[Illustration]
This list includes
the technical publications of the following English publishers:
SCOTT, GREENWOOD & CO. JAMES MUNRO & CO., Ltd.
CONSTABLE & COMPANY, Ltd. TECHNICAL PUBLISHING CO.
ELECTRICIAN PRINTING & PUBLISHING CO.
for whom D. Van Nostrand Company are American agents.
JULY, 1917
SHORT-TITLE CATALOG
OF THE
Publications and Importations
OF
D. VAN NOSTRAND COMPANY
25 PARK PLACE, N. Y.
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Abbott, A. V. The Electrical Transmission of Energy 8vo, *$5 00
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Transcriber's Note
Obvious typographical errors have been corrected. See the detailed
list below.
page 018--typo fixed: changed 'Oregan' to 'Oregon'
page 027--fixed: changed 'Michigian' to 'Michigan'
page 046--typo fixed: changed 'resistence' to 'resistance'
page 058--typo fixed: changed 'homus' to 'humus'
page 069--typo fixed: changed 'resistence' to 'resistance'
page 074--typo fixed: changed 'ilicijolia' to 'ilicifolia'
page 084--typo fixed: changed 'Novia Scota' to 'Nova Scotia'
page 086--typo fixed: changed 'visable' to 'visible'
page 103--typo fixed: changed 'energed' to 'emerged'
page 106--typo fixed: changed 'absolutley' to 'absolutely'
page 110--typo fixed: changed 'has' to 'had'
page 131--typo fixed: changed 'accomodate' to 'accommodate'
page 163--typo fixed: changed 'hydrodeik' to 'hygrodeik'
page 181--typo fixed: changed 'longitutudinal' to 'longitudinal'
page 198--typo fixed: changed 'accomodate' to 'accommodate'
page 202--typo fixed: changed 'ecomony' to 'economy'
page 204--typo fixed: changed 'minumim' to 'minimum'
page 239--typo fixed: changed 'horizonal' to 'horizontal'
page 257--typo fixed: changed 'arrangment' to 'arrangement'
page 266--typo fixed: changed 'applicances' to 'appliances'
page 267--typo fixed: changed 'specialities' to 'specialties'
page 267--typo fixed: changed 'theary' to 'theory'
page 274--typo fixed: changed 'Annual of' to 'Annual or'
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