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Title: Description of the Process of Manufacturing Coal Gas, for the Lighting of Streets Houses, and Public Buildings etc.
Author: Accum, Friedrich Christian
Language: English
As this book started as an ASCII text book there are no pictures available.

*** Start of this LibraryBlog Digital Book "Description of the Process of Manufacturing Coal Gas, for the Lighting of Streets Houses, and Public Buildings etc." ***

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  Transcriber’s Notes

  Text printed in italics has been transcribed _between underscores_,
  bold face text =between equal signs=. ~Text between tildes~ represents
  blackletter text, ^{text} represents superscript text. Small capitals
  have been replaced with ALL CAPITALS.

  More Transcriber’s Notes may be found at the end of this text.

[Illustration: _Pl. II._

_Accums’, Description of Gas Works._

_to Face Title._

_Mulholland Del^{t}._

_W. Read, Sculp^{t}. Maiden Lane, Covent Garden._


_Erected by Order of Government at =THE ROYAL MINT=, by Fredc^{k}.

  ~Gas Works in London,~
  _Accompanied with comparative Estimates, exhibiting the most
  Economical Mode of procuring this species of Light_.

  [Illustration: _Plate I._]



  Lecturer on Practical Chemistry, on Mineralogy, and on Chemistry
  applied to the Arts and Manufactures; Member o£ the Royal Irish
  Academy, Fellow of the Limnæan Society, Member of the Royal Academy of
  Sciences of Berlin, &c. &c.





  _Compton Street, Soho._

The extraordinarily rapid progress which the recent invention of
lighting with coal gas has made in this country, is perhaps without a
parallel in the history of the useful arts.

It was an invention not exempted from the misfortune common to all
innovations on established practises, of encountering opposition, but it
had the fortune common to few, of obtaining an almost instantaneous

A single exhibition of the gas lights in actual use was sufficient to
determine the public judgment in favour of the new mode of illumination;
to see was in this case, indeed to believe.

The legislature responsive to the popular voice, and fortified in its
responsibility, by the results of special enquiries which were ordered
to be made into the merits of the invention, and in which I had the good
fortune to be professionally engaged, gave the most liberal and decided
encouragement to its adoption.

Capital, often wanting even in this opulent country for undertakings of
magnitude, came to the promotion of the new art of procuring and
distributing light in overflowing abundance; and already ere many years
are elapsed, such has been the rapidity with which the gas light
illumination has advanced, that there is not a city and scarcely a town
of any note in Great Britain, in which the art of lighting by means of
gas, has not been carried into effect, or in which active measures are
not in progress, to participate in the benefit of this important

When the art was yet in its infancy, I published a Treatise, containing
a description of the apparatus and machinery best calculated for
illuminating streets, houses, and public buildings, by means of coal
gas, with remarks on the utility, safety, and general nature of this new
branch of domestic economy, as far as then understood, and practised in
the metropolis.

The universal avidity for information on the subject, more perhaps than
any particular merit in the work itself, produced a demand in this
country for four large impressions of this work, in the course of a few
years, and I have also had the satisfaction of finding that the Treatise
has been translated into the French, German, and Italian languages.

Since this work was written, however, the art of manufacturing and
applying coal gas, has undergone so many material improvements, all
combining to bring it to a degree of simplicity, precision, and economy,
far surpassing every thing which the original mode of practice
exhibited, that I have felt I should be guilty of an injustice to the
constant demand which still exists for my former Treatise, had I not
made it my duty to publish the work I now present to the reader;
superseding altogether the former publication, but superseding it from
circumstances of necessity, and with a view to good, which I trust will
be found not illusory.

The present treatise, as its title expresses, is intended to exhibit the
superior process of manufacturing coal gas now employed in the
metropolis and the provincial towns of Great Britain, and to lay before
the reader the elevations, sections, and plans of the improved Gas Light
machinery, which has stood the test of practice, and is now in action at
the most celebrated Gas Light Establishments.

In the first and second part of the Treatise, I have, as introductory
to the rest, given a sketch of the chemical theory and production of Gas
Light. I have pointed out the leading objects of public and private
utility, to which the art of lighting with gas has been, or remains to
be applied: and added such other facts and observations as may serve to
remove all doubt in the minds of the reader as to the important benefit
which this country in particular, and the world at large, have gained by
this discovery.

In the third part I have stated the maximum quantities of gas obtainable
in the large way, from different kinds of coal.

In the fourth part, I have given a description of all the various forms
and dimensions which the distillatory vessels or retorts have
successively assumed, as well as of the improvements that have been made
in the mode of setting the retorts, with a view to saving them from
undue deterioration, and preventing any improvident waste of fuel. I
have here given a particular account of the distillatory apparatus now
used at the most celebrated gas works in the metropolis.

The fifth and sixth parts, lead the reader considerably further into a
knowledge of the economy and practice of this art. They contain an
account of a great variety of experiments which have been pursued on a
large scale, in order to ascertain the most profitable mode of
employing the retorts, the differences of opinion which have existed
among practical men with respect to the degree of temperature fittest to
be applied, and the number of hours at a time during which the retorts
may most advantageously be kept in action, with the particular results
which the experiments instituted into these points have afforded; and
such other data, as will enable the reader to adopt that mode of
operation, which under every circumstance of locality will be found most

The changes which have taken place with respect to the retorts, have
been before detailed in part fourth; but in order to give the
manufacturer a nearer insight into the superior advantages attending
retorts of the construction lately brought into use, I have given in
part seventh, a detailed description of the horizontal rotary retorts,
the application of which has led to a more economical, expeditious, and
easy method of manufacturing coal gas than heretofore practised. I have
distinctly pointed out the advantages which these retorts present, the
particular results they afford, and the method of applying them.

The purification of coal gas forms the subject of part eighth. I have
compared here, the apparatus for purifying coal gas, as it was
originally constructed, with the improved machinery lately adopted,
showing the inefficacy and defects of the former, and the decided
superiority which belongs to the latter.

The ninth part gives an account of the various improved gas holders
which have been invented, and now are in action at the most recent
establishments, for the purpose of storing large quantities of gas. The
improvements that have been made in this department of the Gas Light
machinery, are particularly valuable and have contributed more perhaps
than any other, to lessen the expence of manufacturing gas for
commercial purposes.

In the tenth part, I have given a description of an entirely new
machine, called the gas-metre, or self-acting guage, lately adopted at
the Birmingham, Chester, and other gas works, which measures and
registers the quantity of gas manufactured in any given time, from any
given quantity of coal, or consumed during any period, by any number of
burners or lamps. The great services which such a machine must render
both to the manufacturer and consumer of gas, are particularly pointed
out, and illustrated to the manufacturer, by serving as a complete check
on his workmen as to the quantity of work that ought to be performed,
and to the consumer, as an exact measure of the quantity of gas he
receives, and ought to pay for.

The eleventh part is appropriated to the description of another
apparatus, called the governor, also of recent invention, and now in use
at numerous establishments. The design of this machine is, to regulate
the pressure of the gas, before it enters into the mains, the importance
of which must be sufficiently manifest. I have also pointed out the
application of this apparatus for regulating the magnitude of the flames
of gas burners and lamps.

The twelfth part treats on gas mains and branch pipes, I have here
stated the rules and practical proceedings necessary to be observed, for
applying and distributing gas pipes to the greatest advantage.

The most efficient method of introducing the gas to the interior of
houses, forms the subject of part thirteen. All the necessary
instructions are here given to workmen, for adapting the gas pipes, and
insuring success at the least cost, under every variety of

The fourteenth part gives an account of the illuminating power of coal
gas--the quantity of gas consumed in a given time, by different kinds of
gas burners and lamps, the relative cost of gas, tallow, and oil lights
of different intensities, and the most improved method employed for
ventilating apartments lighted by gas.

In the fifteenth and sixteenth parts, I have added an account of the
manufacture of carburetted hydrogen gas, from coal tar, vegetable tar,
and oil, with such other observations as may enable the reader to form a
proper estimate of the comparative advantage of manufacturing gas from
oil, or tar, under certain circumstances. I have here also given an
account of the manufacture of carbonate of ammonia, as now practised,
from the ammoniacal liquor obtained in the Gas Light process, and of the
manufacture of other saleable products obtainable from coal, namely;
pitch, coal tar, and oil.

In conclusion I have to observe that my object throughout has been to
make the work a compendium of all the best information which the
practice of the art down to the present moment has been able to afford,
embodying a great number of data, with which I have been obligingly
favoured by gentlemen, the most practically versant in the art, and for
which I beg they will individually accept this public expression of my
thanks, and obligations, as well as the results which my own labours in
this department, neither few, nor inconsiderable have furnished.

To supply the reader with a work of practical utility in a most
valuable, and growing branch of national economy has been my object; and
I need scarcely add, that the suffrages of the public to the zeal and
industry at least with which I have endeavoured to obtain that object,
will be a source of infinite satisfaction.


  _LONDON, 1819._




  MEANS OF CARBURETTED HYDROGEN, OR COAL GAS                           1


  AND THEORY OF THE PRODUCTION OF GAS LIGHTS                          33


  OBTAINABLE FROM DIFFERENT KINDS OF COAL                             41


  MANUFACTURING COAL GAS                                              51


  116, AND OF 64 RETORTS, WORKED ON THE FLUE PLAN                     61

  OVEN PLAN LATELY ADOPTED                                            67

  DESCRIPTION OF THE RETORT OVEN                                      69



  OF COAL                                                             80

  CONTAINING TWO BUSHELS OF COAL                                      81





  SPECIES OF COAL IS EFFECTED                                        106


  MANUFACTURING COAL GAS                                             110



  HORIZONTAL ROTARY RETORTS                                          124

  ROTARY RETORTS                                                     134


  PURIFYING APPARATUS, OR LIME MACHINE                               140


  LIME MACHINE LATELY ADOPTED                                        149

  PROPER MANNER OF WORKING THE LIME MACHINE                          157

  GAS                                                                161


  GAS HOLDER                                                         164

  GAS HOLDER AS ORIGINALLY EMPLOYED                                  165

  INTO USE                                                           169

  WORKS                                                              175

  GAS WORKS                                                          177


  DIMENSIONS                                                         185

  COLLAPSING GAS HOLDER                                              185

  DIMENSIONS                                                         195

  RECIPROCATING SAFETY VALVE                                         196





  GAS HOLDER VALVE                                                   221

  SIPHON, OR WATER RESERVOIR                                         221


  GOVERNOR OR REGULATING GUAGE                                       225



  GAS MAINS AND BRANCH PIPES                                         239



  GAS LAMPS AND BURNERS                                              253

  HOUSES                                                             258




  GAS FROM COAL TAR                                                  282

  GAS FROM OIL                                                       289



  COAL TAR                                                           298

  COAL OIL                                                           300

  PITCH                                                              302

  AMMONIACAL LIQUOR                                                  303



  DESCRIPTION OF THE PLATES                                          315

  INDEX TO THE WORK                                                  321

  MANUFACTURE AND APPLICATION OF COAL GAS                            331


  The author of this work respectfully informs the public, that they may
  be furnished with estimates, and plans for the building of Gas Works,
  particularly adapted to the circumstances of the places where they are
  to be established, and that he proposes to superintend the erection of
  the works.

  Mr. Accum also engages to supply the whole of the Gas Apparatus ready
  for immediate use, and to guaranty its efficient performance.

  Or he will contract with any committee, directory, or public company,
  for Lighting with Gas, any Town, Manufactory, or Building, upon
  whatever scale of magnitude, for an annual specific sum.

  Of the qualifications for the services which he thus proffers, he
  would speak with diffidence. Such proofs as he is able to offer of
  them, are to be found in the work here laid before the reader, beyond
  which he would add no more than the flattering testimony of
  approbation, with which his labours have been honoured, in having been
  selected by HIS MAJESTY’S GOVERNMENT to plan and erect the GAS WORKS
  at the ROYAL MINT, and since entrusted with the active management and
  superintendance of that establishment.

  _Compton Street, Soho,

  May 28, 1819._

  The following particulars are required to be stated by those who are
  desirous of receiving estimates, concerning the comparative economy of
  applying coal gas as a substitute for oil, wax, or tallow light.

  1. A plan of the place to be lighted with Gas, drawn to a scale not
  less than one tenth of an inch, to ten feet. The design must exhibit
  the particular spot, where the Machinery is to be erected.

  2. The kind of gas lights required, namely; whether the lights shall
  be equal in illuminating power to one, or more tallow candles of a
  given weight, or equal to an argand lamp.

  3. The number of lights.

  4. The average time the lights are to burn, throughout the year.

  5. The average price of coal, and rate of workmen’s wages, at the
  place where the light is wanted.

  ~Coal Gas~.


_General Nature and Advantages of the art of procuring Light, by means
of Carburetted Hydrogen, or Coal Gas._

The new art of lighting houses, streets and manufactories, with
carburetted hydrogen, or coal gas, is one of those modern discoveries on
which the admirers of science and the inhabitants of this country in
particular, have greater reason to congratulate themselves, than any
other invention or discovery of the present age.

This art is so wonderful and important, it speaks so forcibly by the
effects it has already produced, that it cannot fail to increase the
wealth of the nation by adding to the number of internal resources, as
long as coal continues to be dug in this island from the bowels of the

For if we distribute the catalogue of human wants which a civilized
state of society has introduced, the production and supply of artificial
light, holds next to food, clothing and fuel, the most important place.
We might indeed exist without it, but how large a portion of our lives
would in that state be condemned to a state little superior in efficacy
to that of the animals around us.

If we could for a moment suppose the privation of artificial light,
during the absence of the Sun, it would follow as an immediate
consequence that the greatest part of the globe on which we dwell, would
cease to be the habitation of man. Whether he could ensnare or overtake
those animals upon whose unprepared remains he would then be compelled
to feed; whether he might store the fruits of the earth for his winter
supply--what might be the physical and moral consequences of a state of
such desolation, may perhaps be conjectured, but no estimate can show
its dreadful magnitude.

How much do our comforts, and how greatly does the extent of our power
depend upon the production and supply of artificial light. The flame of
a single candle animates a family, every one follows his occupation, and
no dread is felt of the darkness of night. It might be a curious
speculation to enquire how far, and in what respect, the morals of men
would become degraded by the want of this contrivance. But it is
sufficient on the present occasion, that, previous to entering upon a
dissertation respecting a new art of procuring light, a train of ideas
has slightly been hinted at, which cannot fail to show its magnitude and

The progress of the new art of lighting houses, streets and public
buildings, by means of the inflammable gas obtainable from coal, has
been within these few years uncommonly rapid. The number of gas-lights
already in use in the metropolis alone, amounts to upwards of fifty-one
thousand. The total lengths of mains in the streets through which the
gas is conveyed from the gas-light manufactories into the houses, now
measures two hundred and eighty-eight miles.

The gas-light illumination has also spread far and wide through the
country. Establishments for the supply of the new lights are carried on
at Edinburgh, Glasgow, Liverpool, Bristol, Bath, Cheltenham, Birmingham,
Leeds, Manchester, Exeter, Chester, Macclesfield, Preston,
Kidderminster, and in many other towns and places of Great Britain.

Every body is now convinced that pitcoal is capable of furnishing light
superior to that obtained from oil, wax, or tallow. The public attention
is awakened to the new value of coal, and will not rest till the art of
lighting with gas is pushed to the utmost of its extent.

In order to arrive at a full and accurate knowledge of the many
advantages attending the application of carburetted hydrogen or coal
gas, as a substitute for candles or lamps, it may be necessary,
especially for the information of those readers who have never
personally witnessed this mode of illumination, to take a brief
preliminary view of some of the leading objects of public and private
utility, to which this mode of procuring and distributing light may be
applied, and of the extent to which it is entitled to national

The chief advantages attending the use of gas, are superiority and
uniformity of light, saving of labour, cleanliness, safety and

It must be difficult for a person wholly unacquainted with this art, to
imagine with what facility and neatness gas-lights are managed. The gas
being collected in a reservoir, is conveyed by means of tubes, which
branch out into smaller ramifications, until they terminate at the
places where the lights are wanted. The extremities of the branching
tubes are furnished with burners, having small apertures out of which
the gas issues with a certain velocity corresponding to its degree of
pressure. Near the termination of each tube, there is a stopcock, or
valve, upon turning which when light is required, the gas instantly
flows out in an equable stream. There is no noise at the opening of the
valve, no disturbance in the transparency of the atmosphere; the gas
instantly bursts on the approach of a lighted taper into a peculiarly
brilliant, soft and beautiful flame; it requires no trimming or
snuffing to keep the flame of an equal brightness. Like the light of the
Sun itself, it only makes itself known by the benefit and pleasure it

The gas flame is entirely free from smell. The gas itself has a
disagreeable odour before it is burnt, and so has the vapour of wax,
tallow and oil, as it comes from a candle or lamp newly blown out. This
concession proves nothing against the flame of gas, which is perfectly

The gas-light flame is perfectly steady; a benefit which persons
accustomed to read or write by candle-light, are particularly capable of
appreciating. With the other modes of illumination we have never the
light of the same intensity for two minutes together, independent of
that unpleasant dancing unsteady flame which is so harassing to the

The size, form and intensity of the gas flame, are regulated by simply
turning the stop-cock which admits the gas to the burner or lamp. The
flame may at command be made to burn with an intensity sufficient to
illuminate every corner of a room, or so low and dim, as barely to be
perceived. It is unnecessary to point out how valuable lights of this
description are in nurseries, stables, warehouses, and chambers of the
sick. From the facility with which the gas flame can be conveyed in
almost any direction, from the diversified size and shape which it can
be made to assume, there is no kind of light so well adapted for
ornamental illumination.

The flame of coal gas is of a pure white colour, and of a body full and
compact. In large masses, it becomes of the same flickering character
which is common to all flames of large dimensions, and is owing to the
agitation of the surrounding heated atmosphere.

The saving of labour connected with the employment of gas-light, may
seem on a small scale to be trifling; but when it is considered that in
large manufactories, it is not unusual to find several persons employed
for no other purpose than trimming the lamps or setting and snuffing the
candles of the establishment, the advantage gained on this head by the
use of a species of light which require no sort of attention whatever,
cannot but appear very considerable.

The cleanliness of the gas-lights is also a consideration of no small
importance, they are attended with none of that spilling of oil, and
dropping of grease, which makes the employment of oil-lamps and candles
so injurious in many warehouses, shops and private dwellings.

The flame of a gas-light compared in point of brilliancy to that of a
candle, is as the flame of a common oil lamp, compared to the flame of a
lamp of Argand. The difference between a street, on the night of a
general illumination, and any other night when the street is under the
dull glimmering light of the ordinary oil lamps, is scarcely more
remarkable, than the difference between a street lighted by gas, and one
lighted by oil. While the ordinary oil lamps may be said merely to serve
the purpose of making “_darkness visible_,” the gas-lights really dispel
the dominion of night, and diffuse a body of light so wide-spreading and
intense, as almost to rival the clearest moonshine.

The same brilliancy which makes the gas-lights of such utility out of
doors, in lighting the streets, has been found of equal advantage in
illuminating the interior of private dwellings, and large public
buildings, such as churches, and theatres, &c. From a cluster of
gas-lights, fewer by one-half than the number of oil lamps and candles
required for lighting up a public edifice of this description in the
most ordinary manner, a body of light is furnished which diffuses
through the whole, a degree of mellow clearness which is not to be
attained by the greatest number of oil lamps, or candles, which a due
regard to respiration will admit of being employed. As examples of this,
we have only to name the public theatres of the metropolis, all of which
are lighted with gas, and in a manner which excites universal

It may perhaps be imagined that with a substance so inflammable, and
amidst the blaze of resplendent flame which produces such beautiful
effects, there is a peculiar risk of accidents by fire, but so far is
this from being the case, that gas-lights are the safest of all lights.
No danger can arise from these lights in any way, but what is common to
candle lights and lamps of all kinds, and is the fault of none of them.
The gas-lights are in fact a great deal less hazardous. There is no risk
of those accidents which often happen from the guttering of candles,
from sparks being detached, or from carelessly snuffing them. The
gas-light lamps and burners, must necessarily be fixed to one place, and
therefore cannot fall or otherwise become deranged, without being
immediately extinguished. And further, at any time by shutting the main
tube which conveys the gas to the burners and lamps, all the lights in
the house can be immediately extinguished. In short, where gas is used,
the master of the house, when he has turned the main stop-cock which
conveys the gas into the collateral branch pipes, may retire to rest
free from any of those apprehensions, which before harassed him, lest a
candle might have been left burning, of lest the accidental dropping of
a spark might become the cause of enveloping himself and family in

But the best proof of the great safety of the new lights is, that
notwithstanding upwards of fifty-one thousand gas-lamps burn nightly in
London, we have not heard of a single accident occasioned by them,
though the lamps and burners are generally carelessly managed, while we
have too often occasion to lament the effects arising from sparks of
candles, or carelessness in snuffing them.

Hence the fire-insurance-offices engage to insure manufactories and
public works, at a less premium, where gas is used, than when lighted by
other means.

The excessive expence of insurance, arising from the numerous candles
employed in most of the first-rate manufacturing establishments, and the
combustible nature of the structure of the buildings; the great
difficulty of retrieving the injury resulting to a well-organised
business, from the accidental destruction of the machinery, are
considerations alone sufficient to furnish the strongest economical, as
well as political recommendations, for the adoption of the new lights in
all manufactories where work is done by candle-light.

We have as yet only adverted to the application of gas in the more
ordinary cases where light is wanted, but among other special purposes
to which gas-lights may be applied, it would be improper to overlook the
peculiarly advantageous use which may be made of them in the supplying
of light-houses. From the splendour and distinguishing forms which the
gas-light flame is capable of assuming, nothing can possibly be better
calculated for such a purpose; and in point of economy, the employment
of it would be attended with a saving of at least one half of the
ordinary expence of oil lights. By means of a single furnace, as much
gas may be produced in three hours, as will furnish during the longest
winter night, a flame of greater brilliancy than is now furnished by any
lighthouse in Britain, or indeed in the world. The body of flame may be
increased to any size, merely by increasing the number of burners; and
whatever may be the magnitude of the flame, it will continue to burn,
without becoming in the least clouded by smoke, or the reflectors being
in the least obscured. Should these considerations lead, as it is to be
hoped they will, to the actual employment of gas in the lighthouses
around the British islands, it will readily occur, that in proportion as
the gas would be found attended with less expense than the present mode
of lighting by oil, it would enable the commissioners for light-houses,
out of the surplus means which would be thus placed at their disposal,
to multiply the number of lighthouses, and thus to add most essentially
to the security of British navigation. Nor is it in the case of maritime
signal-lights alone, that the use of gas is applicable, by its superior
efficacy and cheapness. The saving of expences to the country which
would be effected by the substitution of coal gas, for oil and tallow in
these and other public establishments, is a consideration which cannot
be too much pressed on public attention. The annual expenditure for
lighting the barracks of Great Britain alone, is said to fall little
short of fifty thousand pounds; for less than one half of which sum,
they might be lighted by means of gas much better, and a great deal more
safely. Some idea may be formed from the practical saving in this
department--how great might be the total saving, were this new mode of
lighting adopted in all our national establishments.

In the case of the public arsenals, however, the saving from the
employment of coal gas is a consideration of far inferior importance to
the _superior security_ attending it. On the preservation of the stores
which they contain may depend in a time of war the whole chance of
success against the enemy nor can any body who has lived in this
country at such a time have forgot the feverish alarm with which the
people have frequently seen this security endangered by accidents
arising from the use of moveable lights. Were coal gas exclusively
employed in such establishments, the fixed position which can be given
to the burners, and the absence of all danger from sparks must give a
degree of security to those places from fire, far beyond what they at
present possess, even when superintended with the greatest possible
caution and fidelity.

The same remark is equally applicable to the government offices, public
libraries, museums, in short, to all public establishments where the
national value of the articles preserved is such that no _possible_
means of increasing their security from destruction should be neglected.

We have now to turn our attention to another general point of view in
which the introduction of lighting by gas is not less an object of
interest to the public; we allude to the application of gas as a means
of _heating_ as well as lighting. Mr. Maiben[1] was the first who
directed the attention of the public to this subject; he ascertained
that gas from coal gives nearly the same heat when put into combustion,
which is yielded by a third part of the coal from which it is extracted.
In other words, it has been found that a quantity of fuel giving a
particular degree of heat, may be employed so as to produce at the same
time another substance yielding nearly an equal degree of heat in a
different and more manageable form; a form in which it can be preserved
for any length of time, divided into any portions, distributed in any
direction, consumed in an open fire-place, or in a stove concealed in
any shape; a form in which the flame may issue equally well from iron or
from stone-ware, be instantly lighted up and instantly extinguished, be
made to burn as long or as short a time as may suit us, and in any
degree of intensity between the most animating and brilliant blaze and
its total extinction; be extinguished in one room, and the next moment
lighted up in any other; in short such a form, that by one proper
arrangement from the beginning, with the same portion of fuel, we may at
any time have the command of a chearful fire, an adequate and
comfortable warmth in any part of our dwelling to which we may have
occasion to move, as manageable, and in this way as portable, as the
taper by the touch of which it is kindled. To those who have been
accustomed to see before them a solid mass of burning fuel, this gas
flame may at first have the less satisfactory appearance of a fugitive
blaze which we perceive nothing to support. But its uniformity and
permanence will soon banish this impression, while it is attended with
other advantages not inconsiderable with respect either to comfort or
convenience. There are no coals to be carried in, no ashes to be carried
out; there is no blowing, no sweeping of cinders, no dust, no
interruption of servants; there is no excessive heat in one stage, no
sudden damping at another: we have the choice of any temperature, and
which we can regulate with the utmost ease. The fire itself is lively
and pleasant to the eye: inclosed in transparencies it receives a degree
of splendour not easily imagined. Numerous applications of gas, as a
source of heat for airing rooms, and other purposes, have already been
adopted. It is used in kitchens for keeping meat warm, and for boiling
water; in store rooms, in picture galleries, in libraries, for
maintaining them at an equal temperature. By copper-plate printers, it
is used for warming their plates; and by jewellers and other artists,
for soldering.

  [1] _A Statement of the advantages to be derived from coal gas._--p.

It remains further to be observed that the coal, by yielding gas and
other products, namely, tar, pitch, and ammoniacal liquor, is not
entirely lost. It produces, besides light, an excellent fuel, namely,
coke; and as a manufactory, or workshop, generally requires heating as
well as lighting, there is a gain both ways. The manufacturer, by
distilling his coal instead of burning it as it comes from the pit,
saves his candles and improves his fuel. One effort at the outset in
erecting a gas apparatus, will reduce his annual disbursement for those
two articles of prime necessity, much in the same manner, though in a
greater degree, as the farmer gains by building a thrashing machine and
laying aside the use of the flail.

The coal is so far from being reduced in consequence of the gas-light
process, to an useless mass, that in many places immense quantities are
reduced to the state of coke for the purpose of rendering the coal a
better fuel than it was in its natural state; for coke gives a strong
and lasting heat. It is equally valuable for kitchen and parlour fires,
and still more as a necessary requisite in some important branches of
manufacture, so that in whatever quantity coke may be produced, it can
never want a good market. The demand for coke in this capital, since the
establishment of the gas-light works, has prodigiously increased.
Numerous taverns, offices, and public establishments, which heretofore
burnt coal, now use coke to the total exclusion of coal; and in almost
every manufactory, which requires both extensive lighting and heating,
gas and coke are now the means jointly employed. A coke fire emits a
very uniform and intense heat; it produces no sparks, and burns free
from soot and smoke; it requires no trouble in managing, and to those
who have the misfortune of being plagued with a smoaky chimney, affords
the only certain cure.

Another valuable product is the tar which is deposited during the
production of the gas, this tar when rectified by a slight evaporation,
has become an article of commerce. Large establishments, both of coal
tar, coal oil, and pitch, are in full action, and the commodities which
they furnish have become in great demand. The ammoniacal liquor which
the gas-light process affords, has of late given rise to very important
branches of chemical manufacture, carried on upon a large scale. But as
the gas is at present supposed to be the only object in view, for the
sake of the light which it yields, the other products being only
accidentally connected with its extraction, let us leave the idea of
profit on them out of the question, and with the utmost latitude of
concession, require them only to stand as in part for a portion of the
coal employed in the process, we have still the gas, an article which
performs the functions of the oil, the tallow, or the wax for which it
is substituted; and to the price of which we have no need to call the
attention of those who make use of them. There remains only to be
opposed on the other side, the expence of the apparatus by which the gas
is to be prepared, and the lights maintained. From the materials and the
workmanship, with the interest of the capital sunk, the expence in the
first instance, must be very considerable. But where the quantity of
light must be great, even from cheap substances, or where, with a less
quantity of light, the substances from which it is derived must be of
the costliest kind; such is in either case the enormous expence of these
materials, that by superseding them and making every reasonable
allowance to the engineer who erects the gas apparatus, the sum it
costs, both principal and interest, is soon liquidated, leaving at last
a total saving, excepting the expence of accidental repairs, which, from
the durability of the materials employed, seldom exceeds a trifling sum.

The principal expence in the pursuit of this new branch of civil and
domestic economy, is therefore, the dead capital employed in erecting
the machinery for obtaining and conveying the gas. The floating capital,
after the first cost incurred in erecting the apparatus, is
comparatively small; even if usurious interest is allowed for the first
cost of the apparatus, and its deterioration, the saving must always be
considerable, especially if the number of lights furnished are
comparatively in a small place.

At the same time were we to offer advice to the public on this subject,
it would be, that no private individual resident in London, should
attempt to light his premises, for the sake of economy, with coal gas by
means of his own apparatus, whose annual expence for light does not
exceed forty pounds. But when a street, or small neighbourhood is
required to be lighted the operation may be commenced with safety; the
sum required for erecting the apparatus, and the labour attending the
process, together with the interest of money sunk, will then soon be
liquidated by the light and other products.

Individuals have accordingly engaged successfully in the distillation of
coal, and trade with advantage in the articles produced by the process.

In like manner may the lighting of cities be accomplished without the
aid of incorporated bodies; and parishes may be lighted by almost as
many individuals as there are streets in a parish.

The supplying of light to the street or parish lamps alone, of any
district of street lamps only, can never be undertaken with economy in
this capital, nor indeed in any other; for the money sunk in furnishing
the mains or pipes only, must always greatly exceed what any revenue
from the lighting of the streets alone can compensate.

The most beneficial application of gas-lights unquestionably is in all
those situations where a great quantity of light is wanted in a small
place; and where light is required to be most diffused, the profit of
this mode of illumination is the least. Hence, the lighting of the
parish, or street-lamps alone, without lighting shops or houses, can
never be done with economy.

It may be objected to the universality of our conclusion that the price
of coal differing very much in different places will occasion a
variation in the expence of the new mode of lighting.

The price of coals can however have but little effect upon the cost of
the gas-lights; because the very refuse, or small coal, which pass
through the screen at the pit’s mouth, and which cannot be brought into
the market, nay, even the sweepings of the pit, which are thrown away,
may be employed for the production of coal-gas. It makes no difference
in what form the coal is used. This circumstance may contribute to
enable coal-merchants to furnish coals in larger masses, and as they
come from the mine, instead of increasing the bulk by breaking them into
a smaller size, which is a practice commonly followed.

The demand which the gas-light occasions for inferior sorts of coal may
hereafter contribute to lower the price of the superior kinds, and keep
a level which cannot be shaken under any circumstances. It may
contribute to prevent combinations which do certainly operate to the
prejudice of the public, and sometimes put this great town at the mercy
of a few proprietors in the north, who deal out this commodity in any
way they please. The competition thus produced, it is impossible not to
consider as an advantage, which would tend to prevent such combinations,
and put the inhabitants of London out of the reach of them.

The advantages which the coal trade must reap from the introduction of
the gas-light must be very considerable. There is already less waste,
but a greater consumption of coal than formerly. The lower classes of
the community are scantily supplied with firing; and nothing but a
reduction of price is necessary to increase to a very large amount the
average quantity of fuel consumed in the country. The lightness of the
coke produced by the gas-light manufacture diminishing the expence of
land carriage, facilitates its general diffusion--the comforts of the
poor are becoming materially augmented, and a number of useful
operations in agriculture and the arts are beginning to be carried on,
which have been hitherto checked by the extravagant price of fuel. If
any additional vent were wanted for the coke, it would readily be found
in the continental market; coke being better suited than coal to the
habits of most European nations.

Many, and unquestionable as are the advantages of this new mode of
procuring and distributing light, it was not to be expected that an
invention which went to impair a branch of trade, in which a large
portion of skill and capital had hitherto been successfully employed
should escape encountering very considerable opposition. On the first
introduction of the gas-lights, great but happily unsuccessful
endeavours were made to alarm the public mind by dismal forebodings of
the destruction which would ensue to the Greenland trade, and the
consequent loss of a valuable nursery of British Seamen. When
impartially considered it will be found that there was nothing more in
this objection than the common clamour that is always set up against
every new means of abridging labour, to which had the public listened,
an interdict would have been laid upon the spinning and threshing
machines, the steam engine, and a thousand other improvements in

Such clamour scarcely ever fails to be made when the extension of
machinery, the application of inanimate power, and the abridgment of
labour consequent on either, is a matter proposed. We are then sure to
be told that the scheme of mechanical or chemical improvement is pointed
against the human species, that it tends to drive them out of the system
of beneficial employment and that, on the whole, the sum of the
improvement is not only a less proportion of good to society, but a
positive accession of misery to the unemployed poor.

The misfortune of this argument is that to be good for any thing, it
would prove a great deal too much. It is not confined in its scope to
any particular species or defined extent of improvement, but is equally
proscriptive of all improvements whatever. It is a principle for savage
life, not for a state of civilization. It takes for its basis that it is
an advantage to perpetuate that necessity for hard and incessant labour
under which man finds himself originally placed by nature, with all the
wants, privations, ignorance and ferocity, which are attendant on that
condition, and that every discovery, invention, or improvement which
tends to abridge the quantity required of human labour, and to augment
the resources for living and enjoyment is a serious injury to society.
The advocates of this narrow theory do not go the whole length of
maintaining that diminishing labour, and increase of substance, are in
themselves positive evils, a position too absurd perhaps for any one to
uphold; but they maintain what ends in a consequence nearly as untrue,
namely, that neither the one nor the other is of any advantage to
society at large. The palpable error of this theory is, that it supposes
that all improvements which tend to supersede human labour, are
necessarily made for the benefit of a few, and not for the common
benefit of the many; that instead of lessening to each individual the
share of labour requisite to obtain the means of his subsistence, their
only tendency is to lessen the value of each personas labour, and to
oblige him to work more in order to live equally well.

Now, however the existing state of things may be in this country, or in
other countries, arising out of a variety of arbitrary circumstances,
foreign to the natural, and in all cases the ultimately inevitable
course of industry, it is a matter of justice, clear and undeniable,
that every improvement in society ought to be the property of the many,
and not of a few; and that it ought either to lessen the quantity of
labour necessary for acquiring the means of living, or to increase the
profit to be gained by continuing the same quantity of labour. Nor does
there seem any reason for believing that, in point of fact, the actual
distribution of things is so far from according with this principle of
justice as some superficial and prejudiced observers are fond of
representing. The labourer, or artizan, may now work a greater number of
hours daily than he did years ago; but how seldom do we find this to be
the case without his comforts being more than proportionally multiplied,
and his ultimate independence from labour essentially promoted. In
general, however, the fact is, if we may give credit to well informed
economists, that the working classes do not labour more than formerly,
and yet live, or at least have the means of living better; and that by
working even less than formerly, they can obtain the means of living
quite as well.

Let the real state of matters in this respect, however, be as it may,
the question comes to be one merely as to the distribution of the
produce of nature and of art, and instead of opposing improvements
because they tend to encrease that produce, the object of those who have
really the good of their fellow-creatures at heart, ought to be, to
encourage such improvements as much as possible, but at the same time to
obtain a correction of any partiality or injustice which may have crept
into the distribution of their beneficial consequences. It is not to be
denied that all new improvements which interfere with and change the
occupations and habits of the working classes of people, must at first
expose them to inconvenience and distress, against which it is in
fairness the duty of society to protect them; but let not that temporary
inconvenience and distress which can and ought to be provided against,
be held as an insuperable obstacle to the adoption of an improvement the
ultimate tendency of which it is to better the condition of mankind.

It is likewise true that the manufacturing classes often suffer great
want by the occasional suspension of employment, and sometimes actual
oppression, by the demand for labour; but that involves a question more
immediately connected with political economy than the present subject.

It is not the machinery that is in fault in such cases, but those
speculators who occasion an inordinate excess of employment, or those
statesmen who, with their folly, derange the great machine of human
interests and intercourse.

Every invention which tends to diminish the labour of men must be a
benefit to the species; and it is wicked to argue against the use of any
thing from its occasional abuse.

If the application of mechanical inventions thus tends to improve the
humanity of the public, if it reduces the necessity of hard labour, and
diminishes the danger of many occupations which we contend it does, they
who contribute to this object deserve our respect and gratitude.

It may be true that we have now no such minds as those of Homer, or
Bacon, or others of their stamp; but we should reflect that the
circumstances which produced such characters are gone by, and great
faculties have found other objects and other materials to work with.

The use of mechanical industry not only improves and augments the
comforts of domestic life, but it also, perhaps, does as much to soften
the feelings of mankind towards one another as the precepts of
philosophy. It tends to engender a detestation of hard labour, and to
make the world consider not what the labourer may be able to do in
tasking him, but what he ought to do without detriment to himself. It
effects this by withdrawing, to a great degree, from observation, the
distressing spectacle of men and animals toiling beyond their strength.

It ought never to be forgotten, that it is to manufactories carried on
by machinery, and abridgment of labour, that this country is indebted
for her riches, independence, and prominent station among the nations of
the world.

Authentic estimates have shewn, that the use of machinery in Great
Britain, is equivalent to an addition to the population of upwards of
_one hundred millions of adult persons_.

This immense accession of power, has enabled this country to withstand
assaults, and to achieve objects of political ambition, that appear
almost miraculous when compared with the geographical extent and
numerical population of the kingdom.

With respect to what has been advanced as to the probable injury that
would result from the general adoption of the gas-lights all over the
country, to the Greenland trade, it may be observed that the traffic
might with more propriety be called a drain than a nursery of the naval
force. The nature of the Greenland service requires that the crew should
consist of able bodied sailors; and being protected men, not subject to
the impress law, they are rendered useless for national defence. The
nursery of British seamen is the coasting trade; and as the gas-light
illumination becomes extended it will increase that trade as much as it
diminishes the Greenland fishery.

Even on the extreme supposition that it would annihilate the Greenland
fisheries altogether, we should have no reason to regret the event. The
soundest principles of political economy must condemn the practice of
fitting out vessels to navigate the polar seas for oil, if we can
extract a superior material for procuring light at a cheaper rate from
the produce of our own soil. The consequence of lighting our dwellings
and manufactories with gas can in fact prove injurious only to our
continental friends, one of whose staple commodities, tallow, we shall
then have less occasion to purchase, although the new lights can never
supersede entirely the use of candles and moveable lights.


_Outline of the new art of procuring light by means of coal gas, and
Theory of the production of Gas Lights._

All substances, whether animal, vegetable, or mineral, consisting of
carbon, hydrogen, and oxigen, when exposed to a red heat, produce
various inflammable elastic fluids, capable of furnishing artificial

The gases thus obtained are called carburetted hydrogen; they produce,
from their combustion, water and carbonic acid. The species of
carburetted hydrogen, procured from pit-coal, has of late been called
_coal gas_.

We perceive the evolution of this elastic fluid, during the combustion
of coal, in a common fire. The coal, when heated to a certain degree,
swells and kindles, and frequently emits remarkably bright streams of
flame. And after a certain period these appearances cease, and the coal
glows with a red light.

The flame produced from coal, wood, turf, oil, wax, tallow, or other
bodies, which are composed of carbon, hydrogen and oxigen, proceeds from
the production of carburetted hydrogen gas, evolved from the combustible
body when in an ignited state.

It must have been noticed at the same time, that in the common mode of
burning coal in a fire-place, or stove, nearly the whole of this
inflammable gaseous matter is lost. We often see a flame suddenly burst
from the densest smoke, and as suddenly disappear; and if a light be
applied to the little jets that issue from the bituminous part of the
coal, they will catch fire and burn with a bright flame. The fact is,
that the greater part of the carburetted hydrogen gas, capable of
affording light and heat, continually escapes up the chimney, during the
decomposition of the coal, whilst only a small part is occasionally
ignited, and exhibits the phenomena of the flame.

If coal instead of being burnt in the way now stated, is submitted at a
temperature of ignition in close vessels, all its immediate constituent
parts may be collected. The bituminous part is melted out in the form of
coal tar, there is disengaged at the same time a large quantity of an
aqueous fluid, contaminated with a portion of oil, and various
ammoniacal salts. A large quantity of carburetted hydrogen, carbonic
oxide, carbonic acid, and sulphuretted hydrogen also makes their
appearance, and the fixed base of the coal, alone remains behind in the
distillatory apparatus, in the form of a carbonaceous substance called
_coke_. An analysis of the coal is thus effected by the process of
destructive distillation. The products which the coal furnishes may be
separately collected in different vessels. The carburetted hydrogen, or
coal gas, when freed from the foreign gases may be propelled in streams
out of small apertures, which when lighted may serve as a flame of a
candle and then form what we now call GAS LIGHTS.

It is in this manner that from pitcoal a production of our own soil, we
procure a pure, lasting and brilliant light, which in other cases must
be derived from materials in part imported from abroad.

In order to apply this mode of procuring light on a large scale as now
practised with unparalleled success in this country, the coal is put
into vessels called retorts and furnished with pipes connected with
reservoirs to receive the distillatory products. The retorts are fixed
into a furnace, and heated to redness. The heat developes from the coal
the gaseous and liquid products, the latter are deposited into
receivers, and the former are conducted through water in which quick
lime is diffused by which the carburetted hydrogen gas is purified. The
sulphuretted hydrogen and carbonic acid which were mixed with it, become
absorbed by the quick-lime, and the pure carburetted hydrogen is stored
up in a vessel called the gas-holder, and is then ready for use.

From the reservoir in which the gas has been collected, proceed pipes,
which branch out into smaller ramifications until they terminate at the
place where the lights are wanted and the extremities of the branch
pipes are furnished with stop-cocks to regulate the flow of the gas into
the burners or lamps.

The production of gas-lights, is therefore analogous to that of flame
produced from tallow, wax, or oil. All these substances possess, in
common with coal, the elements of certain peculiar matters, which are
capable of being converted into inflammable elastic fluids by the
application of heat.

The capillary tubes, formed by the wick of a candle, or lamp, serve the
office of the retorts, placed in the heated furnace in the gas-light
process and in which the inflammable gaseous fluid is developed. The wax
tallow or oil, is drawn up into these ignited tubes, and is decomposed
into carburetted hydrogen gas, and from the combustion of this substance
the illumination proceeds. In the lamp as well as in the candle, the
oil, or tallow, must therefore be decomposed before they can produce a
light, but for this purpose the decomposition of a minute quantity of
the materials successively, is sufficient to give a good light. Thus
originates the flame of a candle or lamp.

Nothing more therefore is aimed at in the gas-light process, than to
separate the immediate products which coal affords, when submitted to a
temperature of ignition in a close vessel; to collect these products in
separate reservoirs, and to convey one of the products, the inflammable
gas, by means of pipes and branching tubes, to any required distance, in
order to exhibit it there at the orifice of the conducting tube, so that
it may be used as a candle or lamp.

The whole difference between the gigantic process of the gas light
operation, and the miniature operation of a candle or lamp, consists in
having the distillatory apparatus at the gas-light manufactory, instead
of being in the wick of a candle or lamp. In having the crude
inflammable matter decomposed previous to the elastic fluid being
wanted, and stored up for use, instead of being prepared and consumed as
fast as it proceeds from the decomposed oil, wax or tallow; and lastly,
in transmitting the gas to any required distance, and igniting it at
the burner or lamp of the conducting tube, instead of burning it at the
apex of the wick. The principle of the gas-light manufacture is
therefore rational, and justifiable by the general mode in which all
light is produced.

It only remains to be observed that while the new and important use to
which pitcoal may thus be applied, affords a strong confirmation of what
has been well observed, that of all subterraneous combustible
substances, coal is in this country by far the most important natural
production.[2] “It is connected not only with the necessities, comforts
and enjoyments of life, but also with the extension of our most
important arts, our manufactures, commerce and national riches.

  [2] Davy on the Safety Lamp.

“Essential in affording warmth and preparing food, it yields a sort of
artificial sunshine and in some measure compensates for the
disadvantages of our climate.

“By means of it metallurgical processes are carried on, and the most
important materials of civilized life furnished, the agriculturist is
supplied with a useful manure and the architect with a necessary
cement. Not only manufactories and private houses, but even whole
streets and towns are lighted by its application, and in furnishing the
elements of activity in the steam-engine, it has given a wonderful
impulse to mechanical and chemical ingenuity, diminished to a great
extent human labour, and increased in a high degree the strength and
wealth of the country.”


_Classification of Pit-coal, and maximum quantity of gas, obtainable
from different kinds of Coal._

We have stated already that pitcoal is in this country the cheapest
crude natural production from which carburetted hydrogen gas can be
obtained in the large way. It is that which yields it in abundance, and
which can with the least trouble and expence be subjected to the
operation it has to undergo for the production of the gas.[3] Nature has
dealt this mineral out to us, with an unsparing hand, and has provided
mines of coal which seem to defy the power of man to exhaust.

  [3] Other Substances from which carburetted hydrogen gas, may be
  economically obtained, are animal and vegetable oil, tar, both
  vegetable and coal tar; pitch, resin, the essential oils obtainable
  from vegetable and from coal tar, and the compact species of turf. On
  this subject we shall speak hereafter.

The principal coal mines in England are those near Newcastle and
Whitehaven. The town of Newcastle stands on beds of coal which extend to
a considerable distance round the place, and which as far as concerns
many hundred generations after us, may be pronounced inexhaustible.

Pitcoal like all other bituminous substances is composed of a fixed
carbonaceous base in the state of bitumen, united to a small portion of
earthy and saline matter, which constitute the ashes left behind when
the coal is burnt. The proportions of these parts differ considerably in
different kinds of coal; and according to the prevalence of one or other
of them, so the coal is more or less combustible, passing by various
shades from the most inflammable coal into blind coal, Kilkenny coal, or
stone coal, and lastly into a variety of earthy, or stony substances,
which although they are inflammable do not merit the appellation of

All the varieties of coal used in this country for fuel may be divided
into the following classes.

The first class comprehends those varieties which are chiefly composed
of bitumen only, which take fire easily, and burn briskly with a strong
and yellowish white blaze, which do not swell or cake on the fire, and
require no stirring, which produce no slag, and by a single combustion
are reduced to light white ashes. Some of this species of coal when
suddenly heated crackle and split into pieces, especially if laid on the
fire in the direction of the cross fracture of their laminæ.

Cannel coal, deserves to be placed at the head of this class; next to
this, we may rank all those descriptions of coal known in the London
market by the names of Hartley, Cowper’s Main, Tanfield Moor, Eighton
Main, Blythe, and Pont Tops. It also includes the sort of coals found in
several parts of Scotland, called Splent coal, and some of those raised
on the Western Coast of England.

Most of the coals raised in Staffordshire ought likewise to be classed
among this species of coal, but the line of distinction between these,
and the classes subsequently named, cannot be accurately drawn.

The following table exhibits the maximum quantity of gas obtainable from
the first class of coal.[4]

  [4] Own Experiments, made at the Royal Mint Gas-Works.

  One Chaldron of Coal, produces             Cubic feet of Gas.

  Scotch Cannel coal                              19,890
  Lancashire Wiggan coal                          19,608
  Yorkshire Cannel coal,
    (Wakefield)                                   18,860
  Staffordshire coal,[5]
    First variety,[6]                              9,748
    Second variety,                               10,223
    Third variety,                                10,866
    Fourth variety,                                9,796
  Gloucestershire coal,[7]
    First variety, (Forest of Dean, High Delph)   16,584
    Second variety, (Low Delph)                   12,852
    Third variety, (Middle Delph)                 12,096
  Newcastle coal,
    First variety, (Hartley)                      16,120
    Second variety, (Cowper’s High Main)          15,876
    Third variety, (Tanfield Moor)                16,920
    Fourth variety, (Pontops)                     15,112

  [5] They require a much higher temperature, than is necessary for the
  decomposition of Newcastle coal.

  [6] For the maximum quantity of gas produced from this and the three
  succeeding varieties of coal, I am indebted to J. Gostling, Esq.
  Proprietor of the Birmingham Gas Works.

  [7] Most varieties afford a porous, and very friable coke.

The second class of coal, comprehends all those varieties which contain
a less quantity of bitumen, and a larger quantity of carbon than the
first class. They burn with a flame less bright and of a more yellowish
colour, and the last portion of flame they are capable of yielding is
always of a lambent blue colour, they become soft after having laid on
the fire for some time, swell in bubbles and pass into a state of
semi-fusion, they then cohere and coke, puff up and throw out tubercular
scoriæ, with a hissing noise, accompanied with small jets of flame.

In consequence of the agglutination and tumefaction, the passage of air,
if this sort of coal be burnt in an open grate, is interrupted, the fire
burns as it is called hollow, and would become extinguished if the top
of the coal were not from time to time broken into with the poker.

The coke formed from this species of coal is more compact than that
produced from the first sort of coal, and is well calculated for
standing the blast of bellows in metallurgical operations. In respect to
weight the second class of coal is considerably heavier than those of
the first class, the difference amounts to not less than from
twenty-eight pounds to thirty-three pounds in the sack of coal. A
chaldron of some varieties of this class of coal, if the coals are in
large lumps, weighs upwards of twenty-eight hundred weight.

The usual denomination by which the second class of coal is known in the
London market, is that of _strong burning coal_. The following varieties
are sufficiently known, Russel’s Walls-End; Bewick’s and Craister’s
Walls-End; Brown Walls-End, Wellington Main, Temple Main, Heaton Main,
Killingsworth Main, Percy Main, Benton Main, and some varieties of the
Swansea coal.

The smaller kinds of coal of this class are preferred by smiths, because
they stand the blast well. They make a caking fire so as to form a kind
of hollow, space or oven, as the workmen call it. Some varieties abound
in pyrites, and others are intersected with thin layers of slate and
lime-stone. They require more heat for being carbonized than the first
class, and the fluid obtained from it by distillation, contains a
considerable portion of carbonate, sulphate, and hydrosulphuret of
ammonia. They are well calculated for the production of coal gas; the
coke which they produce is not very brittle, and will bear moving from
place to place, without crumbling into dust.

The following table exhibits the maximum quantity of gas obtainable from
the second class of coal.[8]

  [8] Own Experiments, made at the Royal Mint Gas-Works.

  One Chaldron of Coal, produces                   Cubic feet of Gas.

  Newcastle coal,
    First variety, (Russel’s Wall’s End)                 16,876
    Second variety, (Bewick and Craister’s Wall’s End)   16,897
    Third variety, (Heaton Main)                         15,876
    Fourth variety, (Killingsworth Main)                 15,312
    Fifth variety, (Benton Main)                         14,812
    Sixth variety, (Brown’s Wall’s End)                  13,600
    Seventh variety, (Mannor Main)                       12,548
    Eighth variety, (Bleyth)                             12,096
    Ninth variety, (Burdon Main)                         13,608
    Tenth variety, (Wears Wall’s End)                    14,112
    Eleventh variety, (Eden Main)                         9,600
    Twelfth variety, (Primrose Main)                      8,348

The third and last class of coals includes those which are destitute of
bitumen, being chiefly composed of carbon in a peculiar state of
aggregation, evidently combined chemically with much earthy matter.
Coals of this class require a still higher temperature to become ignited
than any of the former classes, they emit little or no smoke. When laid
on a fire they burn away with a feeble lambent flame, indeed some
varieties give no flame at all, but burn merely with a red glow,
somewhat like charcoal, and at length become consumed without caking.
They leave a small portion of heavy ashes.

When submitted to distillation they afford little or no tar; of a
consistence almost resembling pitch, and a gaseous fluid chiefly
composed of gaseous oxide carbon and hydrogen gas. It is scarcely
necessary to add that they are altogether unfit to be employed for the
manufacture of coal gas. The Kilkenny, Welch, and stone or hard coal
belong to this class. They require a strong draught when burnt in an
open fire-grate, and the large quantity of gaseous oxide of carbon which
they furnish during their combustion is extremely offensive. This is
particularly the case with Kilkenny coal. The Welch stone or hard coal
is better adapted for culinary purposes, and there is reason to believe
that this species of coal might be rendered useful in the smelting of
iron ore, by a slight modification in the metallurgic process employed
for extracting the metal from its ore, but to eradicate prejudice, and
to alter established practices is a work which nothing but time can
effect. This species of coal is sent all over the kingdom; it is well
calculated for the operations of drying malt and hops, and its small
coal or culm has been found a more economical fuel, than Newcastle and
Sunderland coals, for the burning of lime and bricks, and for all other
processes where no blazing fuel is required.

The following table exhibits the maximum quantity of gas obtainable from
this class of coals.

  One Chaldron of Coal, produces                      Cubic feet of Gas.

  Welch coal. First variety, from
    Tramsaren, near Kidwelly,[9]                            2,116
    Second variety, from the yard vein at the same place    1,656
    Third variety, from Blenew, near Llandillo              1,416
    Fourth variety, from Rhos, near Ponty Barren            1,272
    Fifth variety, from the Vale of Gwendrath               1,292
    Sixth variety, from ditto                               1,486

  [9] The coal for these Experiments was supplied gratuitously, to the
  Gas Works of the Royal Mint, by Sir W. Paxton of Middleton Hall.

When we consider the before mentioned varieties of coal in an economical
point of view, as fuel to be used in the gas-light process, for heating
the retorts, it appears from a series of experiments that have been made
under my direction, that the second class of coal comprehending those
varieties which contain a larger quantity of carbon than bitumen (p.
45,) afford the most economical fuel, they act less on the grate bars,
and fire bricks of the furnace than those varieties which take fire
easily and burn briskly with a strong blaze. A mixture of Welch Stone
coal, and Newcastle coal forms an excellent economical fuel, where an
intense glowing fire is required.


_Form and dimensions of the Retorts originally employed for
manufacturing Coal Gas._

The proper mode of constructing the retorts in which the coal is
distilled, and the art of applying them form an object of primary
importance in every gas-light establishment. According as the
manufacture is conducted in these respects with a due regard to physical
principles, depends the quantity of gas which can be obtained in any
given time, from any given quantity of coal, the consumption of fuel
requisite for the production of that quantity of gas, the degree of
deterioration to which the distillatory vessel is subjected, the quality
in some measure, of the gas itself; and, as the ultimate result of all
these circumstances, the cheapness at which the gas light can be
furnished to the consumer.

The essential influence of these various particulars on the value of the
art of lighting with coal gas, has led to much assiduous enquiry to
ascertain that sort of construction and mode of operation in respect to
each of them which may be most advantageous. And in no branch of the new
art of procuring light, has a greater variety of plans of improvement
been submitted to the several directing boards of gas works, or more
labour and expence been incurred in experiments conducted on a large
scale, to ascertain the relative merits of these plans. Nor is there any
part of the gas-light process in which a greater number of material
alterations have been put in practice.

In the earlier periods of lighting with coal gas the retorts employed at
some of the gas-light establishments in the metropolis, were hollow
cast-iron cones from six to seven feet in length. The greatest diameter
of the cone which formed the mouth of the retort, measured from twelve
to fifteen inches, and its smallest diameter at the vertex from nine to
ten inches.

At other gas works the form of the retort was a parallelopiped from six
to seven feet long, the horizontal, and vertical sides were
respectively to each other, as 20 to 15 inches. The angles of these
retorts were slightly rounded. Fig. 16, plate V. exhibits a vertical
section of this retort.

Again at other establishments semi-cylindrical retorts, placed
horizontally upon their flat surfaces were employed; fig. 18. pl. V. The
length of these retorts was from five to six feet, and their vertical
and horizontal diameters were to each other as 6 inches, to 18 inches.
And at a few establishments, ellipsoidal retorts, fig. 17, plate V. were
used; these measured from five feet and a half, to six feet in length,
their major and minor axes bore different proportions to each other at
different establishments. At the first adoption of these retorts, the
proportions varied but little from the cylinder, but subsequently the
difference between the major and minor axes became gradually increased
till at last the major axis has become to the minor axis, as 20 to 10
inches, and at some gas works the proportions are as 25 to 10 inches.

With vessels of these forms the distillatory process was carried on for
some years, and the quantity of fuel employed to decompose a given
quantity of coal by means of them, amounted to from thirty to
thirty-six per cent.

When the dimensions of the retorts were increased, both the quantity of
fuel and time required for the decomposition of a given quantity of coal
was in a far greater ratio; and the operations of charging and
discharging the retorts, very troublesome.

Retorts of smaller dimensions have likewise been tried, but the more
frequent charging and discharging, which they require, occasioned such a
waste of time and labour, and such intermissions, in the temperature
necessary for the process of distillation, (besides being attended with
other disadvantages which will be afterwards explained), that they were
speedily discontinued at the gas works where they had been adopted.

The use of conical retorts, as well as of those of a semi-cylindrical
and parallelopipedal form, has of late been discontinued in most
establishments. The conical shape not only diminishes the capacity of
the vessel, but also renders it incapable of being heated economically.

From two comparative series of operations made on a large scale, and
continued for upwards of six months with conical and cylindrical
retorts, with a view to determine the comparative power of these
vessels, it has been proved that the same quantity of gas which can be
obtained by means of forty conical retorts, may be procured in the same
time and with the same quantity of coal and fuel, by means of
thirty-four cylindrical retorts.[10]

  [10] These Experiments were made at the commencement of the new art of
  lighting with gas, at the Westminster Chartered Gas Works, by Messrs.
  Grant and Hargraves.

Similar experiments have been undertaken, to determine the comparative
action of semi-cylindrical and parallelopipedal retorts.[11] The latter,
when kept in action day and night, do not long retain their shape; their
sides collapse, their capacity becomes diminished, their angular form
causes the heat to act upon them unequally, in whatever manner it may be
applied, in consequence of which they suffer more deterioration in some
parts than in others. Besides, they require a much larger proportion of
fuel for decomposing a certain quantity of coal than the cylindrical

  [11] At the Birmingham Gas Works.

Semi-cylindrical retorts, with the base of the retort bent inwards, so
as to give the vessel a kidney-shaped form, have likewise been tried.
But this shape is still less advantageous; they could not be made to
work uniform, they required more heat, and their deterioration was more
rapid than cylindrical retorts. They could not be kept fit for use when
worked day and night, more than about five months. And with regard to
ellipsoidal retorts, it must be confessed, that the experiments that
have as yet been made upon a large scale to ascertain their powers, are
not of a nature to enable us to decide on their merits. No experiments
have been carried on with retorts of this description in the metropolis
for a sufficient length of time, with that care and attention which the
subject demands, to ascertain their comparative power. From what however
has been done, there is reason to believe that ellipsoidal retorts,
might be found more advantageous, than those of a cylindrical form now
in use. An ellipsoidal retort, 20 inches by 10 in diameter, and six feet
long, weighs 14 Cwt.

The reader will thus observe, that of all the forms of retorts which
have been hitherto fairly tried, upon a large scale, it has been
satisfactorily ascertained, (excepting only as to the ellipsoidal
retorts), that the cylinder is the best form for decomposing coal in
masses, from five to eight or ten inches in thickness.

It is perhaps needless to state that in making experiments on the
comparative value of the best form of cast-iron retorts, it is obvious
that the operations should be continued for some months uninterruptedly;
no conclusion can be drawn that may become practically useful in the
large way, from processes carried on for a few weeks only. It is
absolutely essential that the comparative trials be continued for months
together, and that the inferences be taken from the total quantity of
coal used during that period, compared with the total quantity of gas
obtained, the deterioration of the retorts, and the time and labour

Proceeding on erroneous data, many have persuaded themselves of having
noticed that parallelopipedal and semi-cylindrical retorts last longer
fit for use than those of a cylindrical shape, an assertion of which
subsequent trials, conducted in the manner just stated, has clearly
shown the fallacy. Enough has been done at the different gas works in
the capital to settle this point, and there is now but one opinion
amongst those who are best qualified to judge of the subject. Every body
who has made the trial on a large scale, is convinced as already stated,
that the best form of the retort for manufacturing coal gas where the
process is conducted on the plan of decomposing coal in masses or layers
of from four to eight inches in thickness, is a cylinder six and a half
feet long, and one foot in diameter, and accordingly retorts of this
shape and dimensions are now used in all the best regulated gas
establishments in the metropolis.

A cylindrical retort of the description before named, weighs about nine
and a half to ten hundred weight. These and all other shaped retorts are
furnished with a moveable lid or cover having a conical edge to fit the
mouth-piece; the cover is rendered air-tight, not as formerly by
grinding, a mode which was costly, but by the interposition of a thin
coat of loom, between the lid and the mouth of the retort.

The mouth-piece forms a separate part of the retort. It is bolted and
screwed to a flanch which terminates the mouth of the retort, so that
when the retort is worn out, the mouth-piece may be detached and applied
to new retorts.

There are now in action 620 cylindrical retorts, at the two chartered
Gas Works[12] in the metropolis; and the total number of retorts at all
the London gas establishments amounts to 960.


                          { Westminster Station   250 Retorts.
  Westminster Gas Works,  { Brick Lane ditto      190 ditto
                          { Norton Falgate ditto   50 ditto
  City of London Gas Works, Dorset Street,        130 ditto

_Application of heat.--Flue Plan originally adopted._

It must be obvious that the durability of the distillatory apparatus,
greatly depends on the manner in which the heat is applied, to effect
the decomposition of the coal contained within the retort. If the heat
be very intense the whole vessel is rapidly destroyed. If it be too
languid, the distillatory process is protracted, and much fuel, time,
and labour wasted to no purpose; and the retort is speedily
deteriorated, if the heat acts upon one part of it more than upon

The different kind of retorts of which a description has been given in
the preceding pages, were originally heated by means of flues passing
under and over them. The retorts were placed horizontally and fixed in
brick-work. One fire-place at the extremity of the mouth of the retort
where the coals are introduced, and whence the coke is withdrawn, was
allotted to every two retorts in the series.

At the commencement of the new art of procuring light the quantity of
fuel as before stated, necessary to decompose a given quantity of coal,
amounted to from thirty to thirty-six per cent of the coal decomposed;
that is to say, it required from thirty to thirty-six parts of fuel to
decompose one hundred parts of coal. This quantity has been much
lessened by a better mode of setting the retorts, and it is now the
general opinion that the operation of decomposing coal, by means of
cylindrical, parallelopipedal, or semi-cylindrical retorts, must be
considered as well conducted when one hundred parts of coal are
decomposed by twenty or twenty-five parts of fuel. This appears to be
the minimum quantity of fuel, that can be employed for the complete
decomposition of coal by means of these retorts, and with the least
deterioration of the distillatory vessel.

The following statement will exhibit what has been done in this branch
of art.

_Report on a course of Operations, made with sets of 66, of 30, of 116,
and of 64 retorts, worked on the Flue Plan._

In order to determine the relative value of the best method of setting
cast-iron retorts, it was deemed necessary to ascertain whether three
retorts might not be heated, instead of two, as before stated, by one
fire-place and branching flues. To determine this the following
processes were carried into effect.

_Process I._

Sixty-six cast-iron cylindrical retorts, of the usual size, namely, six
and a half feet long, (exclusive of the mouth-piece) and one foot in
diameter, internal dimensions, where set on the plan of three retorts to
one fire-place, at the Westminster gas-work station, and a series of 30
similar retorts were erected at another station belonging to the same
company, at the East end of London.

The experiments were pursued with every degree of justice in the detail,
the retorts were kept in action day and night for upwards of four
months, and the results noted down with exactness. The final reports
from the two establishments were found to concur in showing that nothing
was to be gained by this method over that previously in use.

The time occupied for the distillatory process was not abridged. The
consumption of fuel was greater--no larger quantity of gas was obtained
from the quantity of coal carbonized. The produce with regard to coke
was in the usual ratio, and the retorts were destroyed in about one
third less time than when only two were heated by one fire-place.

_Process II._

The apparently conclusive results of these experiments did not, however,
prevent another set of experiments from being made on the same
principle, extended even a degree farther. The problem now proposed to
be solved, was, whether four retorts might not be heated with economy,
in a manner which had been found already wasteful with respect to three,
that is, whether four instead of two retorts might not be heated
economically by means of one fire-place.

On this plan one hundred and sixteen cylindrical retorts of the usual
dimensions were again erected at the Westminster gas establishment, and
sixty-four at another station belonging to the same chartered company.
These retorts were kept in action in the best possible manner night and
day, and the results, as might have been anticipated, only served to
confirm the facts already established by experiment with three retorts.

Nothing was found to be gained; and so far from their being any saving
in respect of fuel and wear and tear of the retorts, the waste beyond
that which takes place on the plan of two retorts to one fire-place,
was increased to nearly twenty-five per cent., accompanied by a
corresponding acceleration of injury to the retorts.

It was still imagined, however, that the great waste of fuel and the
ultimate unfavourable result of these proceedings, which were repeated
with as little success at several other gas-works in the metropolis with
parallelopipedal retorts, and at other works with retorts of a
semi-cylindrical form, set in a way different from that pursued at the
Westminster station, might probably have been owing to the unavoidable
circumstance, that the heat was not made to act upon all the retorts
employed uniformly in each series of four retorts, but in a manner so
variable that one, or even two of the series would become destroyed and
rendered useless, while the others continued uninjured in a sound and
working state.

The excessive waste of fuel was occasioned, we are told, by the number
of injured retorts, which became useless, and were nevertheless required
to be kept red hot to no purpose; for it was actually found that when
one retort of a series of four became injured, the same fire which had
heated the whole four, still required to be kept up to maintain in
action the remaining three of the series, and so on with respect to the
whole range, till ultimately when there might remain only eighty retorts
actually in use, as many fire-places were required to be in full action
as would have been sufficient to serve for one hundred retorts.

Attempts accordingly were now made to get over this supposed cause of
the losing results, already obtained from the plan of four retorts to
one fire-place, by a new series of similar operations, in which the
retorts were fixed in such a manner, that those which happened to become
injured during the process, might easily and immediately be withdrawn
without materially disturbing the rest, and replaced by new ones. The
waste of fuel was, it is clear, greatly lessened by the expedient; yet
still upon the whole there was no such variation from the general
results obtained by the preceding experiments, as to justify the
adoption of this plan of increasing the number of retorts worked by one
fire-place, on any principle of sound economy.

The great obstacle, as the reader will at once perceive, to working more
than two retorts, no matter whether cylindrical, or of any of the other
forms before named, with economy, by means of one fire-place, evidently
arose from the difficulty of conducting the heat by means of flues
around the series of retorts, in such a manner that the heat shall act
with equal force on all the retorts.

It is almost needless to state, that the construction of the
fire-places, and the direction of the flues for applying the heat to the
retorts, were varied by different workmen, who prided themselves on
being able to aid the object in view, but the result always showed even
that when the draft of the fire-place was well obtained, the action of
the heat upon the series of retorts could not be distributed equally and
kept up uniformly, except at a great expence of fuel and vast
deterioration of the distillatory vessels. The retorts always became
injured more in some parts than in others. The concentration and
rapidity of the draught of the fire, beyond a certain velocity was
always found highly injurious to the retort, and this observation has
been since amply confirmed.

In a well constructed furnace, the deterioration of all the retorts in
the series is uniform over the whole vessel; no part of the retort is
_burnt out_, as the workmen call it, sooner than another part; and
whenever the contrary happens, we may pronounce the fire to be badly
applied. When there is such misapplication of the heat, the manufacturer
cannot depend upon the duration of the distillatory vessel; he is always
in a state of uncertainty with regard to their wear and tear, and it not
unfrequently has happened, under such circumstances, that a whole series
of retorts have become suddenly deteriorated.

_Oven plan lately adopted._

The results before detailed, with regard to the mode of setting
cylindrical retorts suggested the propriety of an entire change in the
mode of applying the heat, and this was at length fully carried into
effect by the adoption of ovens, or air furnaces, in which the retorts
are equally exposed to the action of heat on all sides. Mr. Rackhouse
has the merit of having first carried into effect this method, since
generally known by the name of the _oven plan_.

The first experiments with these ovens were made on only one retort,
exposed in an oven to air intensely heated; but they were afterwards
repeated on two, three, four, and five retorts, successively. The
retorts suffered the action of heat thus applied, exceedingly well;
their deterioration was uniform, and the quantity of fuel required to
work them, was found always to be in a direct ratio to the number of
retorts employed. These experiments were carried on for upwards of nine
months, and it was found, that with five retorts in one oven, so that
the heated air could act upon all of them equally, without the flame
being directed forcibly upon them, this plan had a decided advantage, in
point of economy, over every other method previously adopted. Each oven,
containing five retorts, is heated by means of three fire-places, and
although it is true that the number of retorts is less by one, than what
could have been heated by three fire-places, on the original plan of two
retorts to one fire, yet still this method has been found to be far more
productive. The front wall of the oven may be readily taken down so that
a retort, when damaged, may be withdrawn, and replaced without
materially disturbing the rest.

The oven plan of applying heat has been found equally advantageous for
parallelopipedal and semi-cylindrical retorts.[13]

  [13] The only gas-light establishment of great extent in the
  metropolis, at which parallelopipedal retorts are still in use, is the
  _South London Gas Works_. But it is solely owing to the very peculiar
  care and economy with which all the details of this establishment are
  conducted, under the immediate superintendence of a few active,
  skilful and scientific proprietors, that they are able to compensate
  for the loss, which in all ordinary cases is inseparable from the
  employment of vessels of that description.

_Description of the Retort Oven._

Fig. 1, plate IV., represents a transverse section of one of the retort
ovens now in action at the Westminster Chartered Gas-Light Company’s
Works; similar ovens are likewise in use at the City of London Chartered
Gas-Light Works, and in many other provincial gas establishments.

Fig. 2, plate IV., exhibits a longitudinal section, and fig. 1, plate V.
shows the front elevation of the oven, built about ten feet above the
ground, upon piers or arches, which saves brick-work and allows a stage
or platform to be erected in front of the fire-places of the ovens. See
fig. 2, plate IV.

Between the back part of the ovens and the wall of the building in which
they are erected, is left an empty space of a few inches to prevent the
heat of the oven being communicated to the wall, as is seen at Y in fig.
2, plate IV.

The whole interior of the oven, as well as the horizontal flue which
pass underneath the crown of it, near the upper tier of retorts, is
lined with fire bricks. The uppermost part or crown of the arch is
constructed of large fire bricks of such a shape as will allow to
flatten the upper part of the arch as much as possible, in order to
contract the space between the two upper retorts and the crown of the
arch of the oven.

R. R. fig. 1, and 2, plate IV. and fig. 1, plate V. are cylindrical
retorts, placed horizontally in the oven, the lower series are either
supported by a large fire-brick, placed edgeways underneath the retort,
or by means of a stout wrought-iron pillar, as shown in the design. The
two upper retorts are supported by wrought iron straps, T, T, T, fig.
1, and T, fig. 2, plate IV. The straps pass through the brick-work of
the upper part of the oven, as shown in the designs, and they are
secured with screws and nuts to an iron bearing bar, the extremities of
which are supported by the outer walls of the oven. Each retort is
furnished at the extremity opposite to the mouth-piece, with a short
projecting piece or tail let into the brick-work of the oven, as seen in
the design, fig. 2, plate IV.

M. Fig. 2, plate IV. shows the mouth-piece of the retort with its cross
bar and hand-screw; and fig. 6, plate V. shows the mouth-piece drawn to
a larger scale. E. is the hand-screw, with its cross or bearing bar D,
which passes through the projecting arms C. C. The lid of the
mouth-piece has a conical edge, so that it fits close when pushed into
its place by means of the hand-screw E. Fig. 7, plate V. is the lid
which closes the mouth-piece; the handscrew E, fig. 6, presses the lid
close, to render it air-tight, a thin stratum of loom luting being first
applied to the orifice of the mouth-piece.

F. fig. 2, plate IV., is the fire-place, with the ash-pit E of the
oven. The door of the ash-pit is provided with three slits covered
within by a register slide, to regulate the admission of air as occasion
may require.

The fire passes freely and uniformly round all the retorts, and the
whole cavity of the oven acquires an equable temperature, which it
retains, if the workman takes care to admit as little air as possible,
through the register door of the ash pit, when the upper part of the
arch, or crown of the oven has acquired a bright cherry red heat.

We have stated already that in front of the oven, is a platform, as
represented in the sketch, fig. 2, plate IV. In the floor of this
platform, and directly underneath the mouth-piece of the retorts, all of
which project beyond the brick-work of the oven, is an opening covered
with an iron trap door; through this door the red hot coke, discharged
from the retorts, is suffered to fall below the stage or platform into a
cellar, or other fire-proof place, that it may not annoy the workmen. O,
O, fig. 1, plate V. denotes this opening through which the coke falls.

P, fig. 2, plate IV., and P. P. fig. 1, plate V. is a pipe proceeding
perpendicularly from the upper part of the mouth-piece of each retort,
the other extremity of which descends into the horizontal hydraulic main
H, which is shown in fig. 2, plate IV. and plate V., supported upon iron
columns. This pipe serves to convey away the liquid and gaseous products
which become disengaged from the coal in the retort during the
distillatory process.

The liquid substances, namely the tar and ammoniacal fluid, collect in
the hydraulic main H, plate IV. and V., which is furnished with a
perpendicular diaphragm or partition plate to cause a certain quantity
of the liquid deposited in it to accumulate to a certain height, and
thus to seal the perpendicular pipe P. The liquid cannot flow out of the
horizontal pipe H, till it rises to the level of the diaphragm. This
arrangement is distinctly shewn at H. fig. 2, plate IV., where the
diaphragm or partition plate is seen in the section of the hydraulic
main, together with the extremity of the perpendicular pipe P.,
descending into the fluid contained in the hydraulic main.

K, Fig. 1, plate V. is the discharging pipe, connected with the upper
part of the horizontal main H: it serves to convey away the gaseous and
liquid products from the hydraulic main H. By means of this pipe the tar
and ammoniacal fluids are conveyed into any convenient reservoir, called
the tar cistern, which is perfectly air-tight, and from this vessel the
liquid may be drawn of by means of a pipe or stop-cock. The extremity of
the pipe which communicates with the liquid, is bent downwards, so that
no air can enter the vessel: this arrangement is shown at fig. 3, plate

It is essential that the condensation of the vaporous fluids should be
fully completed before they reach the tar cistern. To effect this, there
is usually allowed a considerable distance to intervene between the
discharging pipe K, fig. 1, plate V., and the reservoir destined to
receive the condensible products; or the pipe is made to pass through a
vessel containing water, called the condenser, which acts in a similar
manner as the refrigeratory of a common still. It is obvious that it is
immaterial how the condensation of the vaporous fluid is effected; it is
essential, however, that the condensation should be complete before the
liquid tar and ammoniacal fluid reach the reservoir destined to receive
these products.

The gaseous fluid which accompanies the condensible products, are then
made to pass into the lime machine, of which we shall speak hereafter,
in order to be deprived by means of quick-lime and water, from the
portion of sulphuretted hydrogen and carbonic acid gas which was
combined with the gas. And when this has been accomplished, the purified
gas is conveyed into the gas-holder, where it is stored up for use. This
part of the operation will be rendered more obvious hereafter. In some
establishments, the hydraulic main is furnished with two discharging
pipes, the one carries away the condensible fluid, into which the
perpendicular pipes P, fig. 2, plate IV. dip, whilst the other serves to
convey away the gaseous fluids to a condensor, in order to deposit the
vaporous portion of condensible liquid it may contain, and from thence
the gas passes into the purifying apparatus, or lime machine. X, fig. 2,
plate IV., is a small screw plug, which, when opened, restores the
equilibrium of the air within and without the retort previous to the lid
being taken off, to prevent the loud report, which otherwise happens
when the lid or cover of the retort is suddenly removed. To avoid these
explosive reports which had become a nuisance to the neighbourhood of
gas works, the practice of gradually withdrawing the lid of the retort,
and at the same time presenting a lighted torch has been adopted at some
works, which fully remedies the evil.

The number of retort ovens at the Westminster Chartered Gas Works’
Stations, amounts to four hundred and ninety.


_Difference in the quantity of Gas evolved during different periods of
the distillatory process, and economical considerations resulting
therefrom in the manufacture of Coal Gas._

In conducting the decomposition of coal, the evolution of the gas is far
from being, with regard to quantity, uniform during different periods of
the distillatory process. The formation of the gas is more rapid in the
beginning of the process, and gradually slackens as the operation
proceeds. The gas also differs in its chemical constitution, at
different periods of the process; although in the case of large
supplies, this difference is of little consequence after the gas is
purified in the usual manner. The former consideration, however, has
given rise to various modes of operating, of which it will be proper to
take some notice.

It must be obvious, that in proportion as the mass of coal in the retort
becomes carbonized or converted into coke, the exterior surface becomes
a gradually increasing obstacle to the action of the heat upon the
interior or central part of the coal remaining to be decomposed. The
heat required on that account must be more intense, and kept up to no
purpose, and the extrication of gas becomes slower and slower, as the
operation proceeds.

The loss occasioned by this rapid diminution of the means employed, is
serious in every point of view, in regard as well to the quantity of
fuel used and time wasted, but it is unavoidable in the operation of
decomposing coal in masses or layers from 5 to 10 inches in thickness,
and must be a great drawback on the value of the gas-light discovery.

The loss of fuel, it is obvious, must be just in proportion to the
quantity of carbonised matter, or coke, which is kept hot to no purpose,
awaiting the decomposition of that portion of coal, which it is the
very means of protecting from becoming decomposed.

A striking exemplification of this statement will be seen in the
following table, exhibiting the result of the progressive produce of
coal gas, obtainable, in a given time, by means of cylindrical and
parallelopipedal retorts.

_Experiment with one cylindrical Retort, containing two bushels of

  Hours of the            Quantity of Gas
  distillatory process       produced.

  First hour               115 cubic feet
  Second ditto              81 ditto
  Third ditto               78 ditto
  Fourth ditto              70 ditto
  Fifth ditto               66 ditto
  Sixth ditto               55 ditto
  Seventh ditto             49 ditto
  Eighth ditto              42 ditto
                           555 cubic feet.

The quantity of gas is at the rate of ten thousand cubic feet to the
chaldron (27 cwt.) of coal.

_Experiment[14] with eighteen cylindrical Retorts, containing one
chaldron of coal._

  Hours of the            Quantity of gas
  distillatory process       produced.

  First hour              2000 cubic feet
  Second hour             1488
  Third hour              1400
  Fourth hour             1301
  Fifth hour              1208
  Sixth hour              1000
  Seventh hour             897
  Eighth hour              691

This experiment was made with retorts set on the flue plan.

The coal employed was (Bewick and Craister’s Wall’s End), Newcastle

  [14] Communicated by Mr. T. S. Peckston, of the Westminster Gas Works.

_Experiment with thirty-six parallelopipedal retorts, each containing
two bushels of coal._[15]

  Hours of the            Quantity of Gas
  Distillatory Process       produced.

  In the first hour           4,058
  Second hour                 3,028
  Third hour                  2,871
  Fourth hour                 2,526
  Fifth hour                  2,380
  Sixth hour                  1,971
  Seventh hour                1,754
  Eighth hour                 1,450

  [15] Own Experiments.

The same heat as we have seen from the preceding table, p. 79, which is
necessary during the first hour of the operation, for the evolution of
one hundred and fifteen cubic feet of gas, is required in the eighth
hour for the production of no more than forty-two cubic feet, being a
decrease in effect of nearly two-thirds.

When larger retorts are employed for decomposing coal in masses, from
five to ten inches in thickness, the loss of heat is in a much greater

In the hope of remedying in some measure the evils thus distinctly
ascertained to arise from the undue thickness of the masses of coal
subjected to the distillatory process, there have not been wanting
manufacturers who have had recourse to experiments on a large scale, to
ascertain with certainty whether they might not be gainers by suffering
the distillatory process, when the retorts are charged with two bushels
of coal, to proceed only for the space of six hours, instead of eight.
But the result of these experiments, as will be presently explained, has
shown satisfactorily that it is more profitable to keep up the
distillatory process for a period of eight hours, with the retorts fully
charged, than to abridge the operation by terminating it at the end of
six hours.

Others again, have imagined, that it would be more economical to
decompose a less quantity of coal at once, or to decrease the thickness
of the stratum of coal in the cylindrical, or in any of the before named
retorts; but then again, serious difficulties occur in the practice.
The more frequent charging of the retorts and luting on the covers,[16]
which such a mode of operating require, occasions a prodigious waste of
fuel, time and labour. A greater number of retorts and more workmen must
likewise be employed, in order to produce the requisite quantity of gas
daily, which the manufacturer is called upon to supply; more space of
ground is required, and more dead capital must be sunk in the
establishment. The more frequent and sudden alterations of temperature
which the retorts necessarily suffer, by the more frequent introduction
of cold coal, renders them extremely liable to become injured; and it is
almost impossible to maintain a number of retorts thus worked, at an
uniform temperature.

  [16] When the cover is ground on, air-tight, the cost of the retort is
  much increased.

From various statements, which I have been favoured with, in
confirmation of my own observations on the best method of working
cylindrical retorts, it may suffice to lay before the reader the result
of a series of operations instituted by one of the largest and best
conducted establishments in this country; the public-spirited and
indefatigable directors of which have done more in the way of extensive,
costly, varied and long continued experiments, to improve the new art of
lighting with gas, than any other similar body in the kingdom; and
without whose exertions the gas light illumination would never have
reached the state of perfection it has attained.

_Report on a course of Experiments made to ascertain the comparative
Economy[17] of manufacturing every week, 857,667 cubic feet of gas, by
means of Cylindrical Retorts variously worked._

  [17] The cost of materials and price of labour in this estimate, as
  well as in all subsequent statements, is given such as they actually
  were, at the time, when the experiments to which they refer were made.

  _Gas Light and Coke Company’s Works,
  Westminster Station._

  _February 8th, 1819._


_Enclosed are the result of a series of experiments made under my
direction with a view of ascertaining the relative value of the
different modes of working cast-iron cylindrical retorts, from which
you will perceive that it is more economical to work eight hours
charges, as the workmen call it, that is to say, to suffer the
distillatory process to go on for eight hours, when nearly two bushels
of coal are contained in each retort, than to discontinue the operation
at the end of six hours._

  _I am with respect,
  Sir, Yours, &c.

  _To Mr. F. Accum,
  Compton Street, Soho._

_Process A._

  Number of|Number |                |                |Quantity|Quantity
  Days the |  of   |Quantity of Coal|  Quantity of   |   of   | of Gas
   Retorts |Retorts| decomposed for |   Coal used    |   Gas  |from one
    were   |  in   | obtaining Gas. |   for Fuel.    |  pro-  |Chaldron
   worked. |action.|                |                | duced. |of Coal.
           |       |_Chal- _Bushel._|_Chal- _Bushel._| _Cubic | _Cubic
           |       |dron._          |dron._          |  Feet._| Feet._
  Monday   |  87   |  10       30   |   4       24   |  94,987|  8,768
  Tuesday  |  88   |  14       24   |   6        8   | 128,597|  8,784
  Wednesday|  88   |  14       24   |   6        8   | 122,188|  8,331
  Thursday |  94   |  15       24   |   6       26   | 131,176|  8,373
  Friday   |  96   |  16        0   |   6       32   | 127,696|  7,981
  Saturday |  96   |  16        0   |   6       20   | 127,536|  7,971
  Sunday   |  96   |  15       18   |   6        4   | 125,487|  8,092
           |       +----------------+----------------+--------+---------
           |       | 103       12   |  43       14   | 857,667|8,300[18]

  [18] Average proportion of gas from a chaldron of coal.

_Expenditure of Process A._

  Coals, decomposed, 103 chaldron 12 bushel, at £ 2. 11_s._
  6_d._ the chaldron, (27 Cwt.)                               £ 266  2 0

  Small Coal, 43 chaldron, 14 bushels, used for fuel, at £ 2.
  2_s._ the chaldron                                             91  2 4

  Wages of two additional workmen (not required had the
  retorts been worked at eight hours charges,) at £ 1. 16_s._
  each man, the week                                              3 12 0
                                          Total expenditure, £. 360 17 0

_Products of Process A._

  Coke, 103 chaldron, 12 bushel, at £ 1. 7_s._ the chaldron   £ 139 10 0

  Breeze, or small coke, 6 chaldron, 9 bushels, at 18_s._ the
  chaldron                                                        5 12 6

  Tar, 7³⁄₄ tons, at £ 6. the ton                                46 10 0

  Ammoniacal liquor, 1864 gallons, at 1¹⁄₂_d._ the gallon        11 13 0

  Gas, 857,667 cubic feet, at 15_s._ the thousand cubic feet     643 5 0
  Total for products,                                         £ 846 10 6

Hence the amount of expenditure for procuring 857,667 cubic feet of gas,
is £ 360. 17_s._

The value of the saleable products £ 846. 10_s._ 6_d._

And the average proportion of gas obtained from one chaldron of
Newcastle coal, 8,300 cubic feet.

_Process B._

  Number of| Number|                |                |Quantity|  Propor-
  Days the |   of  |Quantity of Coal|   Quantity of  |   of   | tion of
   Retorts |Retorts| decomposed for |    Coal used   |  Gas   | Gas to a
    were   |   in  | obtaining Gas. |    for Fuel.   |  pro-  | Chaldron
   worked. |action.|                |                | duced. |of Coals.
           |       |_Chal- _Bushel._|_Chal- _Bushel._|  _Cubic| _Cubic
           |       |dron._          |dron._          |  Feet._| Feet._
  Monday   |  57   |   9       18   |   2      13    |  94,987| 10,000
  Tuesday  |  77   |  12       31   |   3       8    | 128,597| 10,000
  Wednesday|  73   |  12        8   |   3       2    | 122,188| 10,000
  Thursday |  79   |  13        4   |   3      10    | 131,176| 10,000
  Friday   |  76   |  12       27   |   3       7    | 127,696| 10,000
  Saturday |  77   |  12       27   |   3       6    | 127,536| 10,000
  Sunday   |  76   |  12       20   |   3       6    | 125,487| 10,000
           |       +----------------+----------------+--------+---------
           |       | 103       12   |  21      16    | 857,667| 10,000
           |       |                |                |        |  [19]

  [19] Average proportion of gas from a chaldron of coal.

_Expenditure of Process B._

  Coal, decomposed, 85 chaldron, 27 bushels, at £ 2.
  11_s._ 6_d._ the chaldron                               £ 220 16 10¹⁄₂

  Small Coal, 21 chaldron, 16 bushels, used for fuel, at
  £ 2. 2_s._ the chaldron                                    45  0  8
  Total expenditure,                                     £. 265 17  6¹⁄₂

_Products of Process B._

  Coke, 100 chaldron, at £ 1. 7_s._ the chaldron             £ 135  0  0

  Breeze, or small coke, 3 chaldron, at 18_s._ the chaldron      2 14  0

  Coal tar, 6 Tons, 8 Cwt. at £ 6. the ton                      38  8  0

  Ammoniacal liquor, 1536 gallons, at 1¹⁄₂_d._ the gallon        9 12  0

  Gas, 857,667 cubic feet of, at 15_s._ the thousand cubic
  feet                                                         643  5  0
  Total for products,                                       £. 828 19  0

From the result of this process it appears, that at the expence of
265_l._ 17_s._ 6¹⁄₂; the value of the products obtained is £ 828. 19_s._

By comparing the two preceding processes, A and B, it will be observed
that the same quantity of gas was generated each day, notwithstanding
there were fewer retorts in use, and less coal decomposed by process B,
than by Report A, and that the expence of fuel, when the distillatory
process was continued for a term of eight hours, was considerably less.
Also, that the proportion of gas obtained from a chaldron of coals, was
greater than when the process was continued for only six hours.

Hence, if from the products of

                          process A, £. 846 10 6
  we take the products of process B, £. 828 19 0
                   The difference is, £. 17 11 6

which, being subtracted from the difference between the expenditure, as
specified in the process alluded to, namely

  Process A,             £. 360 17  0

  Process B,                265 17  6¹⁄₂
  The difference is       £. 94 19  5¹⁄₂

                     Less    17 11  6
  And leaves a balance of £. 77 17 11¹⁄₂

in favour of _working eight hours charges_, for one week, and producing
a like quantity of gas, as had been obtained by working _six hours

Thus, having compared the quantity of coals actually used when working
six hours charges, with what was used to produce a like quantity of gas
from eight hours charges, I shall next point out, in process C, the
quantity of gas obtained when working the same number of retorts for a
period of eight hours which had been worked at the process of six

_Process C._

  Number of| Number|                |                | Quantity|Propor-
  Days the | of Re-|Quantity of Coal|   Quantity of  |  of Gas |tion of
   Retorts | torts | decomposed for |    Coal used   |   pro-  |Gas to
    were   |  [20] | obtaining Gas. |      Fuel.     |  duced. |a Chal-
   worked. |   in  |                |                |         |dron of
           |action.|                |                |         |Coals.
           |       |_Chal- _Bushel._|_Chal- _Bushel._|  _Cubic |_Cubic
           |       |dron._          |dron._          |  Feet._ |Feet._
  Monday   |   87  |  16      18    |     3    22    |  165,000| 10,000
  Tuesday  |   88  |  14      24    |     3    24    |  146,667| 10,000
  Wednesday|   88  |  14      24    |     3    24    |  146,667| 10,000
  Thursday |   94  |  15      24    |     3    33    |  156,666| 10,000
  Friday   |   96  |  16       0    |     4     0    |  160,000| 10,000
  Saturday |   96  |  16       0    |     4     0    |  160,000| 10,000
  Sunday   |   96  |  15      18    |     3    32    |  155,000| 10,000
           |       +----------------+----------------+---------+--------
           |       | 107       0    |    26    27    |1,070,000| 10,000
           |       |                |                |         |  [21]

  [20] Worked at six hours charges in process A, page 85, but here
  worked at eight hours charges.

  [21] Average proportion of gas from a chaldron of coal.

_Expenditure of process C._

  Coal decomposed, 107 chaldron, at £ 2 11_s._ 6_d._ the
  chaldron                                                    £ 275 10 6

  Small coal, 26 chaldron, 27 bushels, used for fuel, at £ 2
  2_s._ the chaldron                                             56  3 6
  Total expenditure                                           £ 331 14 0

_Products of process C._

  Coke, 124 chaldrons, at £ 1 7_s._ the chaldron           £ 167  8 0

  Breeze, or small coke, 4 chaldrons, at 18_s._ the
  chaldron                                                     3 12 0

  Tar, 8 tons, at £. 6 the ton                                48  0 0

  Ammoniacal liquor, 1945 gallons, at 1¹⁄₂_d._ the gallon     12  3 1¹⁄₂

  Gas, 1,070,000 cubic feet, at 15_s._ for a thousand cubic
  feet                                                       802 10 0
  Total for products                                      £ 1033 13 1¹⁄₂


  Products by process C.        £ 1033 13 1¹⁄₂

  Products by process A.           846 10 6
  Difference                     £ 187 2 7¹⁄₂

  Expenditure by process A.      £ 360 17 0

  Expenditure by process C.        331 14 0
  Difference                     £. 29  3 0

From the above recapitulation it will appear, that by working equal
numbers of retorts, at six and at eight hours charges, the balance is
considerably in favour of the latter method; for, from the foregoing
statement, there appears to be on the practice of the latter method an
increase of saleable products amounting to

                           £ 187  2 7¹⁄₂
              obtained at     29  3 0    less expence;
  consequently there is a  -------------
  balance of                £ 216 5 7¹⁄₂ in favour of

working the retorts, as stated in process C, over that method shewn in
process A; and in such proportion, _let the number of retorts worked be
what it may, an advantage will always be gained in this mode of
manufacturing coal gas, by working the retorts at eight hours charges,
as the workmen call it, in preference to adopting the shorter process_.

From a series of operations made[22] with twenty parallelopipedal and
with twenty cylindrical retorts, worked for one month, it has been
ascertained that the decomposition of coal is most economically
conducted when each retort is charged with 100 pounds of coal, and the
distillatory process be continued for eight hours. Two men, one by day
and one by night, can attend nine or ten retorts.

  [22] By H. Morrison, Esq. and Self; the coal used, was Newcastle
  (Bewick and Craister’s Walls End) coal.


_Temperature best adapted for working Cylindrical Retorts._

There is perhaps no subject in the art of manufacturing coal gas, on
which practical men are less agreed, than they are on the temperature
most economically to be employed for the production of coal gas in the
large way. It must be sufficiently evident, that cast-iron retorts, when
worked at a low temperature, will last longer, than when exposed to
higher degrees of heat.[23] Hence, according to some operators, the
economy of the process consists in saving the retorts, at the expense of
a diminution, even though considerable, in the quantity of gas
obtained; whilst, according to others, it is more economical to obtain
the largest possible quantity of gas at the expence of any consequent
injury to the distillatory vessel.

  [23] It is essential that the retorts should be kept in constant
  action night and day, or at least never allowed to go below a red
  heat. The first portion of oxide which forms upon the surface, when
  allowed to cool, cracks and falls off, leaving a new surface to be
  acted upon the next time it is heated. By thus being every day heated
  and cooled, a retort will be speedily destroyed.

The truth appears to be wholly with neither of these extremes, nor
indeed in any absolute general rule which can be ventured on the

The degree of temperature proper to be adopted in gas works, where the
method of decomposing coal in masses, or layers from four to eight
inches in thickness, and upwards, is practised by means of the cast-iron
retorts, of which a description has been given, p. 53, chiefly depends
on circumstances of a local nature, with regard to the price of coal and
labour, so that where in one place it may be more profitable to employ a
very high temperature for the production of the gas, it may be in others
quite the reverse.

The utmost therefore that can be done on this head, is to state what
these circumstances are, and to shew the value which belongs to them
under every supposable situation.

In this metropolis, and in all other places where coal and labour bear a
higher price than probably elsewhere in this country, and where saving
of time is also an object of primary importance, it is clearly
established, that the manufacturer who pursues the method of decomposing
coal in masses from five to eight inches and upwards in thickness, by
means of cast-iron retorts,[24] will consult his interest best, by
employing such a high temperature for the decomposition of the coal, as
will produce in the shortest time the greatest possible quantity of gas,
from a given quantity of coal, without regarding the unavoidable
deterioration of the retorts. But in places where coal and labour is
cheap, it will be his interest to save the retorts at the expence of the
coal. But that this fact may not rest on mere general assertion, I shall
subjoin for the satisfaction of the reader a few statements of
experiments made upon a large scale for the purpose of ascertaining
these facts.

  [24] The Retorts should be manufactured of what is called in commerce,
  _iron of the second process_. The best cast-iron of this kind, is of a
  light grey colour, its fracture is granulated and dull, it receives a
  dent from the blow of a hammer. The cast-iron which exhibits a dark
  grey or black colour inclining to blue, and presents granular
  concretions, readily friable, and therefore unfit for vessels intended
  to stand a long continued heat.

_Annual Creditor and Debtor Account of manufacturing daily from 50,000
to 102,000 cubic feet of gas at the price which coal bears in the
metropolis.--The operation being commenced with new Retorts, and the
retorts being left in a fit working state._

The first of the following processes was conducted on the principle that
coal and labour, being of an high price, as in London, it is most
economical to obtain the greatest possible quantity of gas from a given
quantity of coal in the least possible time, without any regard to the
injury done to the distillatory vessel.

The second process is intended to illustrate the correctness of that
principle, by shewing that where coal and labour are at the high prices
stated in the first process, it is a losing system to work the retorts
at a lower temperature, in order to make them last longer.

In some respects a similarity will be observed between these
experiments, and those already given in page 85, but besides their
having reference to the separate and distinct circumstance of the high
prices of coal and labour in London, it will be found that they also
differ from the former statements, in exhibiting, not merely the expence
of working, but the original cost of erecting the retorts, as well as
the expence of replacing them.

_Process I._

The quantity of gas to be supplied each night, was 50,000 cubic feet.

In order to produce this quantity, thirty cylindrical retorts, each
containing two bushels of Newcastle coal, were put in action. The
temperature at which the retorts were worked, was a bright cherry
redness, at which they produced at the rate of ten thousand cubic feet
of gas, from a chaldron of Newcastle coal.

To work the retorts, three workmen by day and three by night, were

The retorts were charged three times every twenty-four hours. The first
total expence of erecting the retorts, was £. 23 each, and it was found,
that when worked night and day, they could not, with the utmost care,
be made to continue fit for use for more than from five to six months;
hence, a double set of the original number of retorts was requisite each

The whole annual operation pursued on this plan stood as follows:

  Cost of sixty retorts, thirty at work and thirty to
  spare, with brick-work foundation, iron coke hearth,
  perpendicular pipe connected with hydraulic main, see P,
  fig. 2, plate IV., at £ 23. each.                         £. 1380  0 0

  Six workmen, three during day-time, and three at night,
  at £ 1. 6_s._ each the week                                   405 12 0

  Coals, 1825 chaldron, requisite for producing the gas,
  at £ 2. 8_s._ the chaldron                                   4380  0 0

  Wear and tear of grate bars, fire-shovels, tongs and
  rackers                                                        42  0 0

  456¹⁄₄ chaldron of Coal for fuel, £. 2 1_s._ the chaldron  £. 935  6 3
  Total expence,                                            £. 7142 18 3

  Subtract the market price of saleable
  Coke[25] produced by the process, viz. 1825
  chaldron, at £ 1. 3_s._ the chaldron        £. 2098 15 0

  456¹⁄₄ chaldron of small Coke or Breeze, at
  ten shillings the chaldron                      228  2 6
                                              ------------     2326 17 6
  There remains                                             £. 4816  0 9

for the annual expence of maintaining the apparatus on this

  [25] The tar and ammoniacal liquor afforded by the process, not being
  always saleable articles, are omitted to be charged in the estimates.

_Process II._

The next experiment made was, to ascertain the contrary practice of
operating, namely the mode of working the retorts, on the principle
which holds out, that it is more economical to be satisfied with a less
quantity of gas than what the coal is capable of furnishing, because by
so doing the retorts become less deteriorated and remain for a longer
time in a state fit for use.

The quantity of gas to be supplied each night, was, as in the preceding
process, fifty thousand cubic feet.

The number of retorts required to produce that quantity, was forty-two,
and to make them last twelve months instead of six months, as in the
preceding process, it was necessary to work them at a temperature, at
which a chaldron of coal produces from seven thousand, to eight thousand
cubic feet of gas.

The result of this operation was as follows:

  Cost of forty-two retorts, with brick-work foundation,
  cast-iron coke hearth, perpendicular dip pipe, connected
  with the hydraulic main, at £. 23 each                     £. 966  0 0

  Eight workmen, four by day and four by night, at £ 1.
  6_s._ each the week                                        £. 540 16 0

  2555 chaldron of Coal, requisite for producing the gas,
  at £. 2 8_s._ the chaldron                                £. 6123  0 0

  Wear and tear of grate bars, fire shovels, tongs and
  rackers                                                        42  0 0

  638 chaldron of Coal for fuel, at £ 2. 1_s._ the
  chaldron                                                     1307 18 0
                                                            £. 8979 14 0

  Deduct the market price of 2555 chaldron
  of coke, produced by the process, at £ 1.
  3_s._ the chaldron.                         £. 2938  5 0

  638³⁄₄ chaldron of small coke, or breeze,
  at 10s. the chaldron                            319  7 6
                                              ------------  £. 3257 12 6

  There remains for the annual expence of maintaining the
  apparatus                                                 £. 5722  1 6

  Subtract the annual expence of Process I.                    4816  0 9
  The balance in favour of Process I. is                     £. 906  0 9

_Process A._

In the following additional processes, the retorts when begun to be
worked, were also new, and were left in a fit working state. The
quantity of gas required to be produced daily, was 102,000 cubic

  [26] These Experiments were made at the Westminster Gas Works, under
  the superintendance of Mr. Clegg, to whom I am indebted for this

The retorts were worked at a temperature at which they produced 10,000
cubic feet of gas from the chaldron, (27 Cwt.) of Newcastle coal.

  To sixty-eight retorts, twice replaced, at £ 15. each     £. 2040  0 0

  Deterioration of grate bars, fire shovels, tongs, and
  rackers                                                        91 16 0

  3723 chaldron of coal for obtaining the gas, at £ 2.
  8_s._ the chaldron                                           8935  4 0

  930 chaldron, 27 bushels of Coal, for fuel, at £ 2.
  1_s._ the chaldron                                           1908  0 9

  14 Men at £ 1. 6_s._ each, the week, being 7 for the
  day, and 7 for the night                                      946  8 0
                                                           £. 13,921 8 9

  Deduct the market price of 3723 chaldron
  of saleable coke, at £ 1. 3_s._ the
  chaldron                                    £. 4281  9 0

  930³⁄₄ chaldron of small coke, or breeze,
  at 10_s._ the chaldron                          465  7 6
                                              ------------  £. 4746 16 6
  Cost of obtaining, 37,230,000 cubic feet of gas           £. 9174 12 3

_Process B._

Producing 8000 cubic feet of gas, from the chaldron of Newcastle coal.

  Eighty-five retorts, once replaced at £. 15 each          £. 1275  0 0

  Deterioration of grate bars, fire shovels, tongs and
  rackers                                                       117 16 0

  4653 chaldron of coals for obtaining the gas, at £ 2.
  8_s._ the chaldron                                         11,167  4 0

  1163³⁄₄ chaldron of coal for fuel, at £ 2. 1_s._ the
  chaldron                                                     2385 13 9

  Eighteen men at £ 1. 6_s._ each man the week, being nine
  for the day, and nine for the night                          1216 16 0
                                                          £. 16,162  9 9
  From which deduct 4653 chaldron of
  saleable Coke, at £. 1 3_s._ the chaldron  £. 5350 19 0

  1163³⁄₄ chaldron of small coke, or breeze,
  at 10_s._ the chaldron                         581 17 6
                                             ------------   £. 5932 16 6
  Cost of obtaining 37,230,000 cubic feet of gas,
  according to process B,                                 £. 10,229 13 3

  Deduct the cost of Process A,                                9174 12 3
  Balance in favour of Process A.                           £. 1055  1 0

The reader will have no difficulty in calculating from the preceding
experiments, every variation which can possibly take place, as to the
degree of temperature most economically to be employed in consequence
of a variation in the prices of coal, coke and labour.[27]

  [27] The average cost at which coal gas can be manufactured on a large
  scale in London, is seven shillings the thousand cubic feet, deducting
  not only the interest of the capital sunk in erecting the
  establishment, rent and taxes, the cost of the coal, labour, wear and
  tear of the machinery, and superintendence, but all other necessary
  and incidental expences that may occur.

_Comparative facility with which the decomposition of different species
of Coal is effected._

The temperature necessary for the decomposition of different kinds of
coal, varies. Some species of coal are more readily decomposed, and
require a less portion of fuel than others; they yield up their maximum
quantity of gas, in an almost equal stream from beginning to end, and no
extraordinary increase of temperature is required to terminate the
distillatory process. Other kinds of coal require a different treatment;
the temperature necessary to complete their decomposition requires that
the heat should be considerably increased as the process advances; and
without this condition the evolution of the gas would cease altogether.

A striking proof of this statement may be seen when Newcastle or
Sunderland coal are attempted to be decomposed at a temperature which is
sufficient for the decomposition of Scotch Splent coal, or Lancashire
Wiggan coal.

The decomposition of the latter, will be fully effected when the
distillatory vessel exhibits to the eye a dull cherry redness, and the
evolution of the gas at such a temperature will take place in torrents
from beginning to end. In order, on the other hand, to complete the
decomposition of Newcastle and Sunderland coal, the heat must be
increased as the process proceeds, and the production of the gas will be
extended far beyond the time required for decomposing a like quantity of
Scotch, or Lancashire Wiggan coal, when exposed to the same degree of

It must be allowed, however, that few experiments have been yet made on
this subject. I have reason to believe that all those varieties of coal
which afford an incoherent friable coke, are decomposed at a much lower
degree of heat, than such as produce, when treated under like
circumstances, a ponderous compact coke. And if we give credit to the
assertion of those workmen, whose business it is to manufacture a given
quantity of gas by means of a certain quantity of coal delivered to
them, it would appear that coal which affords gas abounding in
sulphuretted hydrogen, is the kind of coal most easily to be decomposed.
This, as far as it regards the decomposition of Scotch Splent or cannel
coal, is certainly true. No species of coal affords gas at a lower
temperature, and of none is the gaseous product more loaded with
sulphuretted hydrogen gas. The subject is important and deserves to be
pursued; particularly in places where coke is not, as it is in the
metropolis, and all places where coal bears a high price, next to gas,
the primary article to which the attention of the manufacturer of coal
gas ought to be directed.

The following are the result of a series of experiments on the subject
made at the Westminster Gas Works,[28] the same temperature being
employed throughout the process.

  [28] Communicated by Mr. T. S. Peckston.

             Varieties of Coal.                    Ratio of time
                                                    in Decimals.
  Scotch Splent or Cannel coal                          1,00
  Newcastle coal, (Nesham)                              1,04
  Gloucestershire coal
      Forest of Dean first variety (Low Delph)          1,08
  Newcastle coal,
      Second variety, (Middle Delph)                    1,09
      Third variety, (Heaton Main)                      1,15
      Fourth variety, (Brown’s Wall’s End)              1,18
      Fifth variety, (Hutton’s Low main)                1,30
      Sixth variety, (Tyne Main)                        1,54
  Warwickshire coal,
      First variety,                                    1,60
      Second variety,                                   1,65
      Third variety,                                    1,68


_Horizontal Rotary Retorts, lately brought into use for manufacturing
coal gas._

The many disadvantages attendant on the plan of decomposing coal in
masses from five to ten inches in thickness, as already sufficiently
exposed in the preceding parts, had naturally the effect of developing a
principle of manufacturing coal gas, which practice has now fully
established, namely: that to decompose coal, in thin layers from two to
four inches in thickness, is to obtain the greatest quantity of gas from
a given quantity of coal at the least expence.

Mr. Clegg was the first person who pointed out to the public the
advantages that must accrue from this mode of operating, and to him we
are indebted for the construction of an apparatus, the great ingenuity
and superiority of which, entitles what is called the horizontal rotary
retort, to all the merit and praise that belongs to the character of an
original invention.

The numerous and great advantages of this distillatory apparatus, the
rapidly increasing adoption of it,[29] and the almost certain prospect
which exists of their ultimately superseding all former methods of
decomposing coal, make it proper that I should lay before the reader, as
full an account as my limits will permit, of the construction and
operation of this retort, and the mode of applying it; and this becomes
the more necessary on account of the many important improvements which
the apparatus has undergone since its first adoption,[30] and of which
no description has yet been laid before the public.

  [29] Retorts of this description have been lately adopted, in the Gas
  Works at Bristol, Birmingham, Chester, Kidderminster, and at many
  other provincial Gas Establishments.

  [30] An account of the original construction of the rotary retort may
  be seen in the Repository of Arts, No. CLXXVI, 1816, page I. and also
  in the Journal of Science, Vol. II. page 133.

The following account will render the construction of this retort
sufficiently obvious:

_Description of the Horizontal Rotary Retorts at the Royal Mint._[31]

  [31] The retorts lately erected at the Gas Works, at Birmingham,
  Chester, Bristol, &c. are similar to those at the mint.

The horizontal rotary Retorts at the Royal Mint, are hollow cylinders,
eight feet six inches in diameter and 15 inches high, arched a little at
the top. They are made of wrought-iron plates, half an inch thick,
rivetted together in the manner of a steam-engine boiler; A, A, A, fig.
2, plate III. exhibits a perpendicular section of the rotary retort. In
fig. 1, plate II. the retort is seen fixed in the brick-work; _a_, fig.
1, plate II. shews the mouth of the retort, through which the coals are
introduced, and from whence the coke is withdrawn. It is also shown in
perspective at B, B, B. fig. 2. plate VII. The mouth is closed with a
cast-iron door fitted on air-tight by grinding.

The door is connected at its upper and lower extremities, with a frame
and adjusting rod, see B, B, fig. 1, plate II., and also plate VII., by
means of which it may readily be slided down below the mouth of the
retort, when the coals are to be introduced, or coke is to be withdrawn.
To the upper extremity of the rod B, fig. 1, plate II., is fixed a
lever, loaded with a counterpoise weight C, to balance the door, and to
render the opening and closing of it easy and expeditious.

The mouth-piece and its door is three feet long, and nine inches wide;
it projects nine inches beyond the brick-work or furnace in which the
retort is fixed, as may be seen at fig. 1, plate II.

The fire-place, which is on the opposite side to that of the mouth of
the retort, heats only one-third part of the whole capacity of the
retort to that degree which is proper for the complete and rapid
decomposition of the coal, while the remaining parts, which are not over
the fire-place, and to which the fire flues do not extend, are kept at a
lower temperature.

The flues are directed under about one-third of the area of the bottom
of the retort, and after having passed over one-third part of the area
of the top of the retort, they pass into the chimney. Fig. 1, plate VI.,
exhibits the direction of the flues; A, A, the flues, and the
fire-place. The whole retort is guarded from the contact of the fire,
which would soon destroy it, by fire-bricks; it notwithstanding speedily
receives the full effect of the heat, and retains its temperature when
once heated for a long time. Fig. 1, plate II., exhibits one of the
retorts fixed in its furnace. A perspective view of three retorts may be
seen in fig. 2, plate VII.

Through the centre of the retort, passes perpendicularly, an iron shaft
D, as shown in the section of the retort, fig. 2, plate III., and also
in fig. 1, plate II. The lower extremity of the shaft revolves upon the
bottom of the retort, in a cup-shaped cavity, while its upper extremity
passes through the roof of the retort, where the latter is made
air-tight by means of a pipe E, fig. 1, plate II., and E, fig. 2, plate
III., closed at the top and surrounding the shaft, and hence the shaft
must always preserve its centre.

To the lower extremity of the shaft is keyed a box or centre piece,
(technically called a rose centre,) F, fig. 2, plate III. It is also
seen in the perpendicular section of the retort, fig. 1, plate II. From
this shaft radiate twelve wrought-iron arms, G, G, fig. 2, plate
III.,[32] fixed in sockets made in the box. These arms are elevated
three inches above the bottom of the retort, and extend to nearly within
its whole inner circumference. They are wedge-shaped, and their greatest
diameter is at right angles to the base of the retort, so that the
weight of the arms rests on the axis. They are intersected by two
concentric rings, as will be seen on inspecting fig. 5, plate III.,
which exhibits the plan of the retort, together with the iron arms, G,
G, and concentric rings. The centre of figure 5, shows also the plan of
the rose centre F, fig. 2, plate III., into which the arms are keyed.

  [32] In the horizontal rotary Retorts at the Chester, Birmingham and
  Bristol Gas Works, which are twelve feet six inches in diameter, there
  are fifteen arms. At some Gas Works the arms are made of cast-iron.

Between the arms are placed twelve shallow iron trays or boxes, destined
to contain the coal from which the gas is to be obtained. They are
formed to the segment of a circle, hence the whole series of them when
arranged in the retort, exhibits a shallow circular tray, which, when
motion is given to the shaft, may be made to revolve within the retort.

Fig. 12, plate III. exhibits one of the shallow trays, or coal boxes in

It will be obvious, that by the motion of the shaft, any number of the
trays or coal-boxes can readily be brought from the coldest, into the
hottest, and from the hottest into the coldest part of the retort.

H, fig. 1, plate II., and _a_, plate III., or H, plate VII., is a
perpendicular pipe situated at the margin of the retort, close behind
the mouth-piece, and consequently in the coldest part of the retort. It
serves to carry off the distillatory products evolved from the coal, and
causes part of the vaporous tar, which becomes condensed in it, to
trickle back again upon the coal in the retort, in order to become
converted into gas, when the coal on which it falls becomes situated
over the fire-place.

This pipe is furnished at its upper extremity with a _hydraulic valve_,
J, fig. 1, plate II. It consists simply of an inverted cup X, applied
over the upper open extremity of the perpendicular pipe H, and submersed
into a cup formed of a portion of larger pipe, surrounding the pipe H,
containing tar. The smaller, or inner cup X, is represented in the
design raised out of the liquid contained in the outer cup J, to show an
aperture Y, made in the smaller or inner cup; the use of which will be
mentioned hereafter. The inverted cup X, is furnished with a chain, one
extremity of which is fastened to the upper extremity of the cup, the
other passes over a small wheel, and descends through the roof of the
building, as shown in the design.

K, fig. 1, plate II., or K K, fig. 2, plate VII., is a branch pipe
proceeding laterally from the perpendicular pipe H; it communicates with
the hydraulic box L, fig. 1, plate II. N, is a pipe which proceeds from
the hydraulic box L; it serves to carry away the gaseous and liquid
products to their places of destination. The liquid products, namely,
the tar and ammoniacal fluid, become deposited in the tar cistern, fig.
3, plate II., into which the pipe N terminates. The tar cistern is
furnished with two floats Y Y; the one serves to indicate the quantity
of tar, and the other the quantity of aqueous ammoniacal fluid contained
in the vessel. These fluids may be drawn off without admitting air into
the vessel by the stop-cock and bent tube, exhibited in the figure.

The shorter pipe N, which proceeds from the tar cistern, fig. 3, plate
II., and communicates with the purifying apparatus or lime machine, fig.
2, plate II., serves to convey the gaseous fluid, which accompanied the
condensible liquids deposited in the tar cistern, back again into the
lime machine, or purifying apparatus, fig. 2, plate II., the
construction of which, together with the conveyance of the gas from this
vessel to its place of destination will be stated hereafter.

L, fig. 1, plate II., or fig. 2, plate VII., is an iron flap table,
placed level with the bottom of the mouth of the retort. It is
convenient to hold several coal trays ready charged with coal in a state
fit to be introduced into the retort.

The fire-place, flues, and ash-pit of the furnace, in which the retort
is fixed, are sufficiently obvious by mere inspection of fig. 1, plate
II. The front elevation of the retort is seen in fig. 2, plate VII.,
which exhibits three horizontal retorts; two of which have the door of
the mouth-piece slided down, and one with the door in its place, or
shut. The circular ring seen in this design, at the top of each retort,
which rests on iron-bearing bars, the extremities of which are let into
the end walls of the furnace, serves to support the roof of the retort
by means of bolts, proceeding from the inner side of the roof. This
arrangement is likewise shown in the section, fig. 1, plate II.[33] At
the bended part of the perpendicular pipe H, fig. 1, plate II., is seen
a bonnet, or cover, which closes an opening made into the pipe H,
through which, by means of an iron rod, the lower extremity of the pipe
H, may, from time to time, be examined, to guard against an incrustation
of decomposed tar or carbonaceous matter that might happen to accumulate
in that part of the pipe. The upper part of the pipe H, above the bonnet
at the bended part, requires no examination.

  [33] A more economical method of supporting the roof of the retort has
  lately been adopted by Mr. Clegg. It consists in giving the roof the
  form of an inverted arch, supported on the Catenaria plan, by two
  bolts only, placed at the most elevated extremity of the arch and
  secured to an horizontal beam.

_b_, fig. 2, and _b_, fig. 5, plate III., is the flanch of the retort;
_c_, fig. 2, plate III., the flanch of the mouth-piece; _d_, the cutter,
or wedge, which draws the mouth-piece close; _e_, the cross bar, against
which the cutter _d_, bears, to render the mouth-piece air tight; _f_,
fig. 2, one of the eye-bolts or arms which support the cross bar _e_; it
is also seen at _e_, in the plan of the retort, fig. 5, plate II. In
this figure _b_ is the flanch of the retort, and _c_ the door.

These few particulars will be sufficient to enable the reader to
understand the construction of the retort; its action is as follows.

_Action and Management of the Horizontal Rotary Retort._

When the retort is heated to the proper temperature for the
decomposition of the coal, the door is slided down, and the coal boxes
charged with small coal are slided into the retort from the table, L,
fig. 1, plate II., one by one, so that each box rests firmly upon the
concentric rings placed between the arms of the retort; the door is then
slided up again into its place and rendered air-tight by means of

When the whole circle fig. 5, plate III. is thus filled with
coal-boxes, (the coal should be spread in the boxes, in layers two or
three inches in depth,) it is obvious that of all the twelve boxes, four
only can be situated directly over the fire-place, while the remaining
eight are placed right and left towards the door of the retort. The coal
in the former boxes receives the full effect of the heat, (see the plan
of the fire flues of the retort, fig. 1, plate VI.,) while the remaining
eight boxes to which the fire does not extend, are less heated. The coal
in the four boxes which are in the hottest part of the retort becomes
rapidly decomposed, whilst the coal in all the other boxes is gradually
heated, and consequently deprived only of moisture, previous to being
subjected to the greatest heat. The box which is situated under the
condensing pipe H, plate II., near the entry door, receives the
condensed tar which trickles down the pipe H.

Now let us suppose that the coal in the four boxes over the fire place
is fully decomposed, which will be the case if 32¹⁄₂ pounds of coal are
in each box, in two hours, the workman then turns the shaft E, fig. 1,
plate II., one-third part of the circumference of a circle, by pulling
towards him by means of an iron hook the nearest iron arm that may
happen to be opposite to the door; this moves those boxes which at the
commencement of the operation were over the fire-place, towards the
coldest part of the retort, namely, towards the door which is opposite
to the fire-place, and a second series, or four of the adjacent boxes,
are brought in turn into the hottest part of the retort, or over the
fire-place, from whence the preceding boxes were removed.

When the coal in the second series of boxes has been two hours in the
hottest part of the retort, its decomposition will be completed; the
workman therefore turns the shaft again one-third part of a circle, and
a third series advances in their place, while at the same time the first
series becomes situated opposite the entry door of the retort, from
whence they may be withdrawn and exchanged for an extra set of trays,
ready charged with coal and placed on the iron table for that purpose.

In this manner the operation proceeds. One-third part of the whole
charge of coal within the retort is always in the act of becoming
decomposed; another third part is gradually heated, and totally deprived
of moisture, previous to its being exposed to the temperature necessary
for its decomposition; and the remaining third part placed in the
coldest part of the retort, receives that portion of tar, which escapes
decomposition, and trickles down the perpendicular pipe, in order to be
decomposed when the coal upon which it falls becomes situated over the
fire-place. Hence the quantity of tar obtained from one chaldron of
Newcastle coal, when decomposed by means of an horizontal rotary retort,
seldom amounts to more than sixty or seventy pounds, whereas the same
quantity of coal when decomposed by means of cylindrical or
parallelopipedal retorts, yields never less than from one hundred and
fifty, to one hundred and eighty pounds. An horizontal rotary retort,
twelve feet six inches in diameter, and fifteen inches high, furnishes
in the ordinary way of working every twenty-four hours, fifteen thousand
cubic feet of gas, when five trays of the retort are charged with three
bushels of Newcastle coal. The weight of the retort is three tons; its
capacity, one hundred and fifty cubic feet.

The hydraulic valve described page 116, serves merely to restore the
equilibrium, between the gas within the retort, and the atmospheric air
without, previous to the opening of the door of the mouth of the retort.
To effect this the workman raises the cup X, by means of the chain, so
that the small hole Y, in the cup X, becomes raised out of the tar in
the cup L, and he closes it again when the retort is charged: this
operation requires two minutes. We have stated already, that the door of
the retort is ground air-tight, and hence it requires no luting.

_Advantages of the method of manufacturing Coal Gas by means of
Horizontal Rotary Retorts._

The advantages of the mode of manufacturing coal gas by means of
horizontal rotary retorts, consist in a saving of fuel, time, labour,
and machinery, a gain in the quantity of gas, and increase in the
quantity of coke.

_Saving of fuel._--The mass of coal subjected to decomposition being
reduced from the dimension required in the old plan (by means of
cylindrical retorts) to the narrowest available limits, there being no
outward crust of coke to be kept red hot for hours to no purpose, while
the decomposition of the interior mass of coal is going on;--the coke
itself being as soon as formed removed from the source of heat, and
applied while cooling, to warm up a fresh supply of coal next in order
of becoming decomposed, instead of being discharged in a red hot state,
into the open air, as requires to be done in the practice before
detailed--the whole fuel in short being necessarily and beneficially
expended--the saving of coal employed as fuel in this respect, is
exactly the gaining of all that is lost on the plan of employing
cylindrical or any of the retorts before described. Hence one chaldron
of coal is decomposed at the gas establishments where horizontal rotary
retorts are in action by means of twenty per cent of fuel, and at some
establishments an expert stoker will work the retorts with fifteen per
cent of fuel.

_Saving of time._--The saving of time does not merely amount to what is
consequent on the speedier decomposition of the coal, and the saving of
that heat which formerly required to be kept up a length of time to no
adequate purpose; it also includes all that is gained in consequence of
the revolving motion to which the coal is submitted, superseding, as has
been already mentioned, the necessity of discharging the coke in an
ignited state from the retort.

When the coke is removed, as previously explained, page 72, red hot from
the cylindrical, parallelopipedal, semi-cylindrical or ellipsoidal
retorts, the charging of the distillatory vessel with fresh coal
produces such a sudden reduction of temperature, that from three to four
hours inevitably elapse before the retort is again in a full working
state, and to this circumstance the workmen (perhaps very justly)
attribute the frequent sudden injury which the distillatory cast-iron
vessel sustains.

Another striking advantage of the new mode of decomposing coal is, that
besides saving the time which is wasted in keeping up an intense
temperature unnecessarily the revolving apparatus prevents entirely the
loss occasioned by these three or four hours of unnecessary cooling of
the distillatory vessel. For each series of trays, or coal boxes,
containing the ignited coke, of the horizontal rotary retort, being
suffered to cool within the retort before the coke is discharged, and
being placed in contact with a fresh supply of coal, the temperature of
the retort is kept up uniformly the same from beginning to end.

_Saving of Labour._--In consequence of the superior facility with which
the mode of decomposing coal in thin layers and removing the coke as
fast as it is formed is effected, the saving in point of labour is very
great. The charging and discharging of the retort is performed in two
minutes. Hence one chaldron of coal may be decomposed by means of three
horizontal rotary retorts, each twelve feet six inches in diameter, and
with the attendance of two men, in eight hours, and produces from
fifteen thousand, to eighteen thousand cubic feet of gas, whilst ten
thousand cubic feet of gas can only be obtained from the same quantity
of coal in eight hours, by means of twenty cylindrical retorts, attended
by the same number of workmen.

_Saving of machinery._--When we compare the original cost and wear and
tear of the horizontal rotary retorts, with the cost and deterioration
of a set of cylindrical, parallelopipedal, ellipsoidal, or
semi-cylindrical retorts of an equal power, (that is to say to produce a
like quantity of gas, in a given time,) a difference not less striking
presents itself in favour of the horizontal retort.

We have stated already, that cylindrical, ellipsoidal, parallelopipedal,
or semi-cylindrical retorts, when constantly kept in action, and worked
to the greatest advantage, cannot be made to last longer than six

  [34] They are frequently rendered unfit for use in three months, and
  at some works in two months, owing not less to the irregularity of the
  temperature at which they are worked, than to the carelessness of the

Only one-third part of the top and bottom plates of the rotary retort
being exposed to the action of heat, are alone liable to deterioration.
It is only necessary therefore that these parts of the vessel be
renewed, while the other parts remain uninjured for years. The new top
and bottom plates being rivetted to the old and undecayed part, without
deranging the rest, the retort is rendered as good as new.

_Gain in the quantity of gas._--A large increase in the quantity of gas
obtained, is a natural consequence of the mode in which the
decomposition of coal is effected by means of the horizontal rotary

Every body knows that coal, when decomposed slowly, affords a larger
quantity of tar and ammoniacal liquor, but a less quantity of gas than
when decomposed rapidly.

In the former case, the formation of the proximate products which coal
is capable of furnishing is effected properly; the bituminous part of
the coal is developed under the most favourable circumstances.

But when coal, after being previously deprived of moisture, is very
suddenly heated to a high temperature, in thin strata, and small
portions at a time, so that the vaporous products instead of becoming
condensed, are made to come into contact with a substance (which in this
case is the roof of the retort,) kept constantly at a temperature rather
higher than that at which gold, silver, and copper melts, (32°,
Wedgwood, or 5237°, Fahrenheit,) a very different arrangement of
principles takes place.

The greatest portion of tar which the coal is capable of furnishing,
instead of being produced in a liquid form, becomes then decomposed into
carburetted hydrogen, and olifiant gas. That portion of tar which
escapes decomposition, is condensed in the perpendicular pipe _H_, fig.
2, plate II., or _H_, fig. 2, plate VII., and falls back again into the
retort, where it is also decomposed when the coal upon which it falls
comes under the process of decomposition.

Hence the quantity of tar obtained by means of horizontal rotary
retorts, is very small; it seldom exceeds the proportion mentioned page
123, when the retort is worked to the greatest advantage. This quantity
is considerably diminished, when Newcastle coal, broken into pieces of
the size of split pease is decomposed in strata, not exceeding two
inches in thickness. The quantity of tar afforded by a chaldron of coal
then amounts to thirty pounds, whilst at the same time the quality of
the gas is improved; because coal tar furnishes olifiant gas, which the
coal alone, when distilled by means of cylindrical or other shaped
cast-iron retorts of the usual form, cannot produce, or at least but in
a small quantity. One gallon of coal tar yields 15 cubic feet of
olifiant gas, which greatly increases the illuminating power of the
carburetted hydrogen.

From what has been so far stated, it will be understood why one chaldron
of Newcastle coal, when decomposed by the new process, may readily be
made to produce from 15,000 to 18,000 cubic feet of gas and upwards,
whereas the same quantity of coal, if decomposed by the old method,
yields only upon an average 10,000 cubic feet of gas.[35]

  [35] The experiments exhibiting the maximum quantity of gas obtainable
  from coal, see page 44, were made with the horizontal rotary retorts
  at the Royal Mint. Similar results have also been obtained at the
  Westminster Gas-Works.

In the former case, the greater part of the essential oil and tar which
the coal would have afforded is decomposed, as stated already by virtue
of the high temperature to which the vapourous tar is suddenly exposed
in the horizontal rotary retort, which is not the case when coal is
decomposed in the retorts of the old construction.

_Gain in the quantity of coke._--With the cylindrical or cast-iron
retorts of the old shapes, the quantity of coke obtained from a given
quantity of coal is upon an average 25 per cent. increase by measure
from the best kind of Newcastle and Sunderland coal, but taking into
account the waste incurred in breaking out and removing the red hot coke
from the retort, which requires the application of rakers and crow bars,
a considerable portion of it becomes reduced to dust or breeze, and
hence no more than bulk for bulk of the coal decomposed can seldom be
depended upon as the ultimate saleable quantity of coke.[36]

  [36] There is a vast difference with regard to the quality as well as
  quantity of coke obtained from different kinds of coal. Some kinds of
  coal produce a species of coke which is so friable that it will hardly
  bear being moved from place to place without crumbling into dust,
  others produce coke in pieces of the size of small pebbles, while a
  third sort affords coke of a stony hardness.

In the new mode of carbonizing coal by means of the horizontal rotary
retorts, the increase of coke is 150 per cent. by measure, so that one
chaldron of Newcastle coal produces two and a half chaldron of
coke--this is the quantity produced upon an average. But when the retort
is worked at a temperature to produce at the rate of 18,000 cubic feet
of gas from the chaldron of coal, the increase of coke by measure is 175
per cent.; in that case, the layers of coal in the coal boxes must not
exceed two inches in thickness, so that the volume of coke is in the
ratio of the quantity of gas produced and the rapidity and elevation of
temperature at which the decomposition of the coal is effected.

The coke being withdrawn from the place where it is formed by merely
turning the boxes containing it, upside down, all waste is avoided.

With respect, again, to the quality of the coke, it will be observed
that when the coal is rapidly carbonized in thin layers, and has full
liberty to expand freely, as in the case of the horizontal rotary
retort, it affords a light and porous coke, whereas in the cylindrical,
paralellopipedal, semi-cylindrical, or ellipsoidal retorts, the coke
being compressed, the intense heat to which it is so long and
superfluously exposed, renders it extremely dense, and of a stony

The latter sort of coke is unquestionably preferable for the smelter,
and all furnace operations, standing the blast of the bellows well. But
the coke produced in the new mode of operating, is better suited for
the great majority of domestic purposes, kindling more readily, and
making a more cheerful fire. The combustion of the dense, or as it is
now called, cylinder coke, can be only kept up when used in a common
grate, by a strong draft of air, and it is therefore not so well suited
for fuel for domestic purposes, to make a small fire; but the coke
obtained by the horizontal rotary retort, readily maintains its own
combustion, even when in small masses; hence it may be used without any
trouble, either in the fire-place of the cottager, or of the prince, and
accordingly it bears a higher price in the market.

_Directions to workmen, with regard to the management of Horizontal
Rotary Retorts._

The circumstance most essential to the economical application of the
horizontal rotary retort, is, as has been repeatedly stated, that the
coal shall be spread in thin layers in the boxes of the retort, not
exceeding from two to four inches in thickness; and it may be laid down
as a general rule, that the thinner the layers, and the higher the
temperature, the greater will be the proportion of gas, the greater the
bulk of coke, and the smaller the quantity of tar.

The coal before it is submitted to the distillatory process, should be
as dry as possible, and the more it is comminuted the better. The very
refuse of the coal called _slack_, provided it is perfectly free from
foreign matter, answers best. It should also be spread in the trays, in
even layers.

When the retort is in a good working state, the temperature should be
kept up by the application of small quantities of fuel at a time. A
prodigious saving of fuel may be effected by attending the fire
properly, and it is this which distinguishes a careful stoker from a
bungler. For in the working of this retort particularly, it is a
wasteful process to clog up the fire-place with a large quantity of fuel
injudiciously applied. The difference in this respect, with regard to
the economy of fuel is so great, that an expert stoker will work the
retort with one-third less of fuel and half the labour that would be
employed by a negligent workman.

The quantity of gas produced from a chaldron of coal may be ascertained
by the gas metre, or by the gas holder, if the outlet valve of the
latter be shut during the distillatory process.

The heat at the same time employed for working the retort, will be best
defined for the stoker’s guide, by copying carefully on paper the red
tint of the retort, as seen through the sight hole, made for that
purpose in the brick-work directly over the fire-place.

The first six feet of the perpendicular pipe H, fig. 1, plate II., which
conveys the distillatory products from the retort, should be well
cleaned out once a month, the bonnet at the bended part of the pipe H,
fig. 1, is provided for that purpose, as already stated, page 119.

When the retort remains uncharged, the fire must be kept low in order to
prevent its getting beyond the usual temperature, and the arms and
moveable axis should be turned occasionally, and the door kept close.

The fire tiles which cover the flues under the retort should be examined
about once a fortnight, and if a tile is melted or broken, it must be
replaced by a new one, because the preservation of the retort greatly
depends upon this precaution.

All the parts of the arms composing the moveable disc within the retort,
may be taken out of the door of the retort, if they should require a
repair, first taking off the cap from the perpendicular pipe E, fig. 1,
plate II., surrounding the shaft of the retort, then the centre piece,
or rose centre, F, fig. 2, plate II., the shaft D, fig. 2, plate III.,
may be drawn up through the pipe which surrounds it.

When the retort requires cleaning, which should be done once every six
or eight months, a screw may be attached to the upper extremity of the
shaft D, which passes through the retort; by this means, the arms and
rose centre within the retort can easily be raised, to leave the bottom
of the retort quite clear, in order that the lumps of coke, that may be
scattered about, may be easily removed. And if an incrustation of coke
should happen to be attached to the bottom of the retort, it may be
readily detached by a crow bar, or other suitable instrument.

The trays or coal boxes, fig. 12, plate II., may be made by the stoker,
of sheet iron, (called in commerce No. 16,) framed upon a wooden mould
made for the purpose.

The temperature best suited for the decomposition of coal by means of
the horizontal rotary retort depends, as has been already stated in the
case of cylindrical cast-iron retorts, altogether on the price of coal,
and the price which can be obtained for the coke.

In all places where the average price of coal, equal in quality to
(Bewick and Craister’s Walls End) Newcastle coal, or any other species
of coal, capable of producing from fifteen to eighteen thousand feet of
gas from one chaldron, is not less than £ 2. 8s. the chaldron (27 Cwt.)
or upwards, and where coke can be sold at the average price of £. 1 the
chaldron, the horizontal rotary retort should be worked at such a
temperature, that when viewed through the sight hole, it shall appear of
a bright cherry redness, and at which it produces from 15,000 to 16,000
cubic feet of gas, from a chaldron of coal.

But in all other places where coal of the same quality to (Bewick and
Craister’s Walls End) Newcastle coal, may be purchased at £. 1 8s. the
chaldron, or at a less price, it will be more advantageous to the
manufacturer, to work the horizontal rotary retort, at a lower
temperature, so as to produce only at the rate of thirteen or fourteen
thousand cubic feet of gas from the chaldron of coal. In the latter case
the manufacturer expends coal in order to save his retort, whereas in
the former case he economizes the fuel, as productive of a gain more
than commensurate for the waste of the retort.

When the supply of gas required, happens at any time to be less than the
retort when in action is capable of furnishing, the fire must then be
kept low, but the retort should never be suffered to acquire a lower
temperature, than that of a dull red heat visible by day-light.


_Purifying Apparatus, or Lime Machine._

Coal gas, even as obtained from the best species of coal, must be
rendered pure before it is fit for the purpose of illumination. The gas
in its crude state always contains a portion of sulphuretted hydrogen
and carbonic acid; and when burnt, although its illuminating power is
greater in an impure than in a pure state, it produces an oppressive and
suffocating odour, which is speedily perceptible in confined places. The
gaseous product evolved during its combustion, blackens paint and
tarnishes metallic bodies; an impure gas besides strongly acts upon the
copper branch pipes through which it is conveyed.

To obviate these defects the sulphuretted hydrogen and carbonic acid
which are the cause of them must be removed, and to effect this, no
method more economical and efficacious, has as yet been discovered, than
to bring the gas confined under a pressure equal to a column of water,
not less than eight or ten inches in height, into contact with
quick-lime, diffused through water. Other means have been tried, but all
of them have failed to be sufficiently efficacious or economical on a
large scale.

_Lime Machine originally employed for the Purification of Coal Gas._

In the lime-machine, until lately in use, the gas was made to pass in
the apparatus, through passages which could not be guarded from being
stopped up in the course of time by the concretion of a quantity of
carbonate and hydro-sulphuret of lime, formed during the purification of
the gas, so that when the stoppage occurred, a prodigious pressure was
produced in the machine, in consequence of which, it was either found
impossible to keep the distillatory apparatus air-tight, or if this was
accomplished, a great part of the gas was forced through the purifying
apparatus, without coming in contact with the lime, by driving the
column of mixture of lime and water before it, and of course without
being rendered fit for use, previous to its passing into the gas
reservoir. This effect was unavoidable without the precaution of
employing a very dilute mixture of quick-lime and water.

Numerous instances have also occurred where from the increased pressure
which the gas exerted in the lime apparatus, the tar from the hydraulic
main was driven up with a prodigious force through the dip pipe, P, fig.
2, plate IV., into the retort when the retort was opened, where it took
fire to the imminent danger of the whole establishment.

The apparatus originally employed was composed of a large vessel closed
on all sides to receive the gas; within this was a smaller vessel or
lime trough open at top containing the quick-lime and water; and there
was also a third vessel, or inverted trough into which the gas was

This inverted trough was open at bottom, and the edge of the open part
was immersed beneath the surface of the mixture of lime and water
contained in the lime-trough, so that the gas which was introduced in
the last-mentioned inverted trough could not escape therefrom, except
rising up through the lime and water. To facilitate this, holes or
openings were made in the inverted trough near the bottom edge thereof,
and beneath the surface of the purifying mixture, so that the bubbles of
gas were obliged to rise up through these openings. From this
construction of the machine the apertures through which the gas had to
pass, were extremely liable to become stopped up, and dangerous
consequences ensued.

In order to remedy in some measure the evil, a plan was adopted by Mr.
Malam, for making the gas to pass in thin strata underneath a series of
shelves, placed horizontally in the machine so as to expose the gas in
as large a surface as possible to the contact of the lime and water, and
employing the purifying mixture at the same time in a more dilute
state:--this arrangement is as follows.

Fig. 4; plate V., represents a vertical section of the machine; it is
made of cast-iron plates, rendered air-tight by screws, bolts, and iron
cement. It consists of three separate chambers, _a_, _a_, _a_, destined
to contain the mixture of quick-lime and water. At the under side of
each chamber, is bolted a cylinder, _h_, _h_, _h_, the lower extremity
of which is furnished with a large flanch, extending nearly to within
the whole inner diameter of the machine.

From the bottom of each of the chambers, _a_, _a_, _a_, proceeds a pipe
curved upwards, and communicating with a circular vessel, C, C, C, which
serve for the purpose of charging the chambers, _a_, _a_, _a_, with the
mixture of quick-lime and water, and regulating the level of the fluid
within the chambers. The curved pipe likewise prevents the escape of the
gas when the contents of the chambers _a_, _a_, _a_, are discharged.

The vessels, C, C, C, are provided with a waste pipe and stop-cock, as
shown in the sketch, for discharging the contents of one chamber into
the chamber placed below it, and lastly into the reservoir _e_.

_b_ _b_, are pipes which convey the gas into the chambers, one extremity
of each pipe communicates with the cylinders _h_, _h_, _h_, and the
other with the chamber below it, and the lower pipe communicates with
the valve M, so that by this means a communication is formed from the
lower cylinder _h_, to the middle cylinder _h_, and from the middle to
the uppermost cylinder. K, is the exit pipe which conveys the purified
gas from the uppermost chamber into the reservoir destined to receive
it. Through the centre of the machine passes a wrought-iron shaft,
furnished with agitators or arms, to stir up the mixture of quick-lime
and water. The arms are not immediately connected with the shaft, but
proceed from cast-iron hydraulic cups, of the usual construction, by
this means the escape of the gas is prevented, nor can the fluid pass
from one chamber into another. The axis is put in motion, by wheel-work
as shown in the design _e_, the handle for turning the shaft.

_g_, is a receiver to collect the condensible products. The contents of
this vessel may be discharged by a hand pump being attached to the upper
extremity of the pipe _f_, after the cap with which it is closed is

The operation of this lime machine is obvious. The gas first passes into
the lowermost chamber of the cylinder _h_, where it comes in contact
with the purifying mixture and passes through the fluid to the top of
the same chamber, and thence through the pipe _b_, into the cylinder
above it which communicates with the lower chamber, where it is acted on
again by the lime and water, and bubbles up through the fluid to the top
of the chamber. From this compartment the gas passes into the third
cylinder, where it bubbles up and passes through the lime and water; and
lastly it makes its exit through the pipe K, into the gasholder or
vessel destined to receive it.

When the mixture of quick-lime and water in the compartments _a_, _a_,
_a_, of the machine, requires to be renewed, it is let off by the
stop-cock at the bottom of the lowermost vessel into the reservoir _e_.
The fluid contained in the upper chamber may be discharged into the
chamber below it, and so on with the chambers below it, care being taken
to close the stop-cock of the lower vessel. The machine may be recharged
at the uppermost chamber with the purifying mixture. Fig. 5, exhibits
the plan of the machine. _b_, _b_, _b_, the tubes connecting the
chambers. B, the flanch of the cylinder _h_.

This machine has in part remedied the inconveniences stated pages 141,
142, but the increase in the quantity of the purifying materials which
the apparatus requires, is of itself productive of most serious

The greater accumulation of waste lime which such a practice occasions,
renders it necessary that capacious reservoirs and sewers should be
constructed to receive and carry off the refuse materials, and where an
outlet by such means cannot be obtained, the carting away the increased
quantities of waste matter adds greatly to the cost of the gas.

If attempts are made to convey the waste substances into the common
sewers or drains of the neighbourhood, the proprietors of gas works are
exposed to indictments for a nuisance at the suit of the inhabitants,
and when the near proximity of any river or lake induces an attempt to
convey the waste materials thither, the most serious injury may be done
to the water, which becoming impregnated with hydrosulphuret of lime is
rendered unfit not only for domestic but for many manufacturing
purposes. The latter evil indeed is one which operates also in a greater
or lesser degree, even when the fœtid refuse or hydrosulphuret is
discharged into the common sewers, all of which ultimately empty
themselves into some water course, rivulet or lake. I would here beg to
suggest, that considering how rapidly the new mode of procuring light is
extending throughout Britain,[37] and how much the waters of the country
are liable to be contaminated, from discharging into them the noxious
refuse from the process of purifying coal gas, so as to be rendered
proportionably unfit for the various purposes of domestic and
manufacturing economy, it is well deserving the attention of the
legislature, whether such contamination ought not to be guarded against
by prohibiting enactments.

  [37] The Towns of Edinburgh, Glasgow, Liverpool, Bristol, Bath,
  Cheltenham, Birmingham, Leeds, Manchester, Exeter, Macclesfield,
  Kidderminster, Preston, Waterford, Rochester, Chatham and several
  others, have been lighted with gas within these few years.

It appears to me that it would be a wise exertion of authority, to
insert in every act of Parliament granted for incorporating Gas-light
Companies, a clause prohibiting the proprietors from ever conveying the
waste material, or any other produce from the manufacture of coal gas,
either directly or indirectly into the common sewers, drains or water
courses, or into rivers and lakes adjacent. The salubrity of the water
we use is of as much consequence to us, as any superior excellence or
saving of cost in our light can possibly be, and we ought to take care
that in profiting by an improvement which science and art have
discovered, we do not unnecessarily depreciate one of those primary
blessings we owe to the bounty of nature.

_Lime Machine lately adopted._

In the improved purifying apparatus[38] lately brought into use, of
which we shall now give an account, a shaft or axis furnished with teeth
or claws, is applied within the interior of the vessel, and made to act
in such a manner as to scrape out the openings or slits through which
the gas has to pass every time the axis is moved round, and by which
regular clearance all chance of stoppage is avoided without any
augmentation of the purifying mixture.

  [38] This machine has been adopted at the gas works at Chester,
  Birmingham, Kidderminster, Bristol, and in many other provincial Gas

The lime trough is also made moveable on a centre or axis, in such a
manner that it may readily be inverted by a lever from the outside, for
the purpose of emptying its contents into the bottom of an exterior
vessel, from which the waste materials may be discharged at pleasure.

With this machine we are farther enabled to employ the purifying mixture
in a semi-fluid state, and consequently in a much less bulk; and after
having suffered it to remain in the reservoir destined to receive it,
the waste substance speedily acquires such a degree of solidity that it
may be dug out with a spade and carted away in a small compass. The
safety of the apparatus is therefore insured and the construction of
expensive drains and sewers is rendered unnecessary. The following
description will render the construction of the improved apparatus

A, A, fig. 2, plate II., is a rectangular four-sided prism, made of
cast-iron plates, screwed together air-tight with bolts and cement. The
base of the prism terminates in a rectangular four-sided pyramid placed
with its apex downwards. It is surrounded by an iron stage, supported
upon pillars, as shown in the design.

Within this vessel, which in fact composes only the outer case of the
apparatus, is contained an oblong trough B, fig. 2, plate II., (it is
shown in the design as if broken down), moveable upon an horizontal
axis, fixed to one of its longest sides, so that by means of the wheel
C, or lever communicating with the axis, and applied on the outside of
the machine, the trough B, may be inverted, and its contents discharged
into the exterior case, or lower part A, A, of the machine. The part B,
of the machine is called the lime trough, because it is destined to
contain the quick-lime and water, by means of which the crude coal gas
is purified. Within this trough B, is inverted an oblong rectangular box
D, closed at top and open at bottom, called the air-box, because it
receives the gas to be purified.

In each of the longest sides of the box D, are perpendicular openings or
slits (as shown in the design) exactly opposite to each other. Through
the whole length of this box D, passes a horizontal axis furnished with
as many teeth or claws as there are upright openings, through each side
of the box. These claws extend a little way through the openings so that
when the axis, which passes through a stuffing box, is made to revolve
by means of the handle X, the ends of the claws pass through the
openings and scrape them out every time the axis is turned. The claws
operate first on the openings of one side of the box and then on those
on the opposite side. They pass quite through and therefore keep them
clear; those parts of the claws which enter into the openings are narrow
in the direction of their motion, and that part of each claw which is
nearest to the centre, is broad and flat, hence they act as paddles or
rowers whilst they are in motion, to stir up the quick-lime and water.

Fig. 10, plate III., represents a transverse section of this part of the
apparatus. B, B, is the lime trough; D, the air box inverted into the
lime trough; the dotted circle shows the sweep of the claws when the
shaft is put in motion. The darts show the course of the gas.

Fig. 10, plate VI., represents a plan of the machine. G, shows the
inverted air-trough with its axis, and the claws or teeth fixed upon the
axis. H, is the lime trough. A, the outer case of the machine; R, R,
the axis, to which is affixed the wheel or lever, for inverting the
trough H. L, the axis and handle to give motion to the shaft upon which
the claws are fixed, for stirring up the contents of the lime trough.

The inverted air-box D, fig. 2, plate II., is supported within the outer
case of the machine A, A, fig. 2, plate II., by cross bars, and the axis
is put in motion by the handle X, on the outside of the machine. It is
rendered air-tight by a stuffing box, and is provided with wheel-work,
as shewn in the design, fig. 2, plate II., to communicate the motion to
the axis.

The gas is brought into the air box by the pipe N, fig. 3, which
proceeds from the tar vessel, fig. 3, plate II. The gas cannot escape
out of the machine without displacing the column of fluid in the lime
trough, in order to make its way through the openings or upright slits
in the side of the air box D, and thus bubbling up through the mixture
of quick-lime and water, the depth of which is one foot. The
sulphuretted hydrogen and carbonic acid being thus made to combine with
the lime, the carburetted hydrogen is left more or less pure, it is
conveyed into the gas metre, by the pipe V, where it is to be measured,
and from thence by the pipe W, fig. 4, into the gas-holder.

When the purifying mixture is to be removed, the workman unbolts the
wheel C, fig. 2, and turns it half way round; (if the emptying of the
lime trough requires more power than can conveniently be applied by
means of the wheel, the axis of the trough may be worked with a tooth
and pinion, a small wheel being attached to the axis of the pinion as a
perpetual handle;) this motion inverts the lime trough B, and its
contents become discharged into the outer case forming the inverted
pyramid of the apparatus, whence the waste materials may be conveyed
into the reservoir or pit Q, by drawing open the sliding valve _o_, fig.
2, plate II., or _o_, fig. 3, plate VII., added for that purpose to the
discharging pipe P, fig. 2, plate II., or _p_, fig. 3, plate VII. To
prevent the air entering into the machine when the waste lime is
discharged, the lower extremity of the outlet pipe P, dips into the
basin Q, fig. 2, plate II., which always contains a portion of the waste
fluid and thus seals the extremity of the pipe P.

One side of the lime-machine is provided with two large lenses, to
admit light into the interior of the apparatus, so that by means of an
eye-glass fixed in a proper place, the workman is enabled to see into
the interior of the apparatus. And when the machine requires to be
cleaned out, the _manhole_ as it is called, is opened for the workmen to
enter into the apparatus to remove any solid incrustation of carbonate
of lime, or hydrosulphuret of lime that may happen to be formed in the
lime trough, or any other part of the apparatus.

The wheel C, is loaded with a counter-weight, to balance the weight of
the lime trough. To bring the lime trough again into a proper position,
to be re-charged with a fresh portion of the purifying mixture, the
workman turns the wheel C half round, the contrary way to that which
caused the trough to be turned topside-down, and the trough may then be
re-filled with a fresh portion of lime and water from the reservoir R,
fig. 2, plate II., (or R, fig. 3, plate VII.,) containing the mixture
ready prepared. Y, is a pipe to bring water from a cistern into the lime
reservoir R. The prepared lime which is to supply the machine is put
into the vessel R, and a sufficiency of water being mixed with it, the
mixture is stirred up to the consistence of a semi-fluid mass.

T, shows the pipe furnished with a sliding valve S, for conveying the
purifying mixture of quicklime and water into the lime trough from the
reservoir R, which is furnished with an agitator to stir up its

To give motion to the shaft for stirring up the contents of the lime
trough D, the inventor of this machine (Mr. Clegg,) has happily applied
the gas, to act as a power for that purpose. This operation will be
explained hereafter in describing the gas metre.

The pipe N, which conveys away the purified gas, proceeds from an
hydraulic valve, to cut off the communication between the gas holder and
the lime machine, if occasion should require it, and to prevent the gas
from passing back from the gas holder into the lime machine.

It consists of a box containing water into which dips a small pipe, by
means of which the gas passes out of the lime machine, and from thence
into the pipe V, communicating with the gas metre. The box is furnished
with a tube curved upwards to discharge the water when it accumulates
above the required height, and to prevent any quantity being thrown out
of the hydraulic valve, by the concussion of the fluid in the lime

One cubic foot capacity of the lime trough is sufficient to purify 1000
cubic feet of gas obtained from Newcastle coal in twenty-four hours.

_Test Apparatus, for certifying the purity of coal gas, and the proper
manner of working the Lime Machine._

The proper purification of the gas being a matter of essential
importance, as already illustrated page 140, it becomes of great
consequence to have some ready means of ascertaining whether the workman
does his duty in this respect, by keeping the lime trough D, fig. 2,
plate II., properly charged with the requisite quantity of lime and
water necessary for the purification of the gas.

For this purpose an apparatus has been adapted by Mr. Clegg to the lime
machine, which serves not only to indicate the quantity of fluid
contained in the machine when gas is manufactured, but which also
enables the workmen to appreciate the quantity of quick-lime necessary
for the purification of the gas, and to ascertain its purity. The
apparatus consists of a closed cup C, fig. 23, plate IV., partly filled
with any coloured liquid. Into this cup is cemented, air-tight, a
straight glass tube _a_, about 2¹⁄₂ feet long and a ¹⁄₄ of an inch in
the bore; the lower extremity of the tube nearly touches the bottom of
the cup, and is therefore sealed by the fluid. _d_, _d_, is a small
copper tube, which forms a communication between the air confined above
the surface of the fluid in the guage cup C, and the gas which is
proceeding into the lime-trough.

The communication may be established at any part of the pipe which
conveys the gas into the lime machine. When the connection is made, the
fluid in the guage cup C, will be driven up into the perpendicular
measuring tube _a_, by the pressure of the gas, to an altitude equal to
a column of liquid contained in the lime-trough. It is essential that
the tube _a_, be at least 2¹⁄₂ feet in height, if the depth of the
lime-trough is one foot, for without this precaution, the fluid will
rise out of the tube in consequence of the oscillation which it suffers.
By this means the overseer of the works will be enabled, by mere
inspection, to know whether the workmen have charged the lime trough
with the mixture of quick-lime and water to the requisite height, which
should never be less than from ten to fifteen inches. Because the
abstraction of the sulphuretted hydrogen and carbonic acid gas, from the
carburetted hydrogen with which it is combined, is greatly facilitated
by pressure, and there is no inconvenience whatever in operating under a
pressure of a column of fluid of even double the height that has been
stated, provided the apparatus is properly constructed. From experiments
made on this subject, I am justified in stating that one half of the
quantity of quick-lime that is required for the purification of coal gas
in the ordinary way, is sufficient, if the column of the liquid opposed
to the gas is raised to twenty inches high, nor is the evolution of the
gas in any degree retarded under such a pressure.

The curved tube _d d_, which is cemented air-tight into the gauge cup
_c_, has a free communication with the gas in the guage cup _c_. It
serves to enable the workmen to form some notion of the chemical
constitution of the crude gas, before it passes into the lime machine.
For if the stop cock _e_ of the tube be opened, and the descending leg
_a_ of the bended tube _d_ be immersed in a glass containing a solution
of super acetate of lead, some notion may be formed by a little practice
of the quantity of lime requisite for the purification of the gas, from
the quantity of (black precipitate) hydrosulphuret of lead produced. Two
per cent of quick-lime to the coal employed (if Newcastle coal) is
usually sufficient for the complete abstraction of all the sulphuretted
hydrogen and carbonic acid, contained in the crude gas, provided the
operation be carried on under a pressure of not less than a column of
water twelve inches in height.

The test tube _f_, properly so called, may be adapted to any part of the
pipe which conveys the purified gas to its place of destination. It
serves to ascertain the purity of the gas, after it has been acted on by
quick-lime, by suffering the gas to pass from the tube into a solution
of super acetate of lead, which speedily becomes discoloured, if the
gas contains sulphuretted hydrogen. The presence of carbonic acid is
rendered obvious, by a white precipitate being produced when the gas is
made to pass through barytic water. The precipitate, which is carbonate
of barytes, effervesces with acids.

It must be obvious that the apparatus which we have now been describing
does not require to be placed in the immediate vicinity of the gas light
machinery. It may be arranged in the counting-house of the overseer,
who, by mere inspection, can then at all times detect the slightest
irregularity or insufficiency in the process thus given to the gas light
manufacture, a degree of scientific controul of which few arts can

The following method has been found economical and convenient, for
preserving quick-lime in a ready state, fit for the purification of coal

Take the lime as soon as possible after it is burnt; put it into a pit
eight or ten feet long, five or six wide, and five or six deep,
constructed of brick-work and level with the ground. By this pit set a
wooden trough about six feet long, three feet broad, and two feet deep.
The trough should have at one end a hole about six inches square,
covered with an iron grating, the bars of which are a quarter of an
inch distant. Let this grating be provided with a slider, which can
occasionally be drawn up to uncover, or pushed down to cover, the
grating. Put three or four bushels of lime at a time into the trough;
throw water on it, and mix it up into a thick fluid mass with a hoe
perforated with holes. When there is a good quantity of liquid, draw up
the slider and let the slacked lime run into the pit. Throw more water
on the remaining unslacked lime, and lastly reject those pieces which
will not slack. The trough should have a small inclination and project
over the pit.

After the lime thus slacked has been five or six hours in the pit, it
will take the consistence of a stiff paste, which it retains for years.
It should then be kept covered to keep it clean and to exclude the free
contact of the air. For those who use larger quantities of lime, several
pits should be constructed in preference to one larger reservoir. When
the lime is wanted for use it may be dug out with a spade, and readily
diluted with a sufficient quantity of water.

The quick-lime thus prepared forms a perfect homogeneous mixture. The
practice of throwing lime simply slackened into the lime cistern is a
wasteful and slovenly process, as will becomes obvious on examining the
waste hydrosulphuret of lime discharged from the machine, which will be
found to abound with lime in a concrete form, unacted on by the
substances with which it was intended to combine.


_Gas Holder._

The name of gas holder, or, as it is improperly called, gasometer, is
given to the vessel employed for collecting the gas and storing it up
for use. In the principle and construction of this part of the gas light
machinery, peculiarly valuable improvements have of late been made. They
have contributed to lessen the expence of the apparatus so much, that a
reservoir for storing up any quantity of gas, may now be furnished for
nearly one half the sum which such a vessel cost as originally

In the infancy of the art of lighting with coal gas, the reservoir was
encumbered with a heavy appendage of chains, wheel-work and balance
weights, and from the construction of the machine, it was necessary to
guard it from the impulse of the wind, the action of which on the gas
holder, would have rendered the lights which the machine supplied with
gas, unsteady.

Hence it was necessary to inclose the gas holder in a building, called
the gasometer house, which formed one of the largest items of
expenditure which the proprietor of a gas light establishment was called
upon to defray.

Now, however, the whole of these expensive appendages is dispensed with,
nor is the gasometer house to contain the gas holder any longer
necessary, and the machine as now constructed may be fixed in the open

_Gas Holder as originally employed._

The gas holder, of the original construction, consists of two principal
parts; first, of a cistern or reservoir of water, usually constructed of
masonry, or of cast-iron plates, bolted and screwed together; and
secondly, of an air-tight vessel which is closed at top and open at
bottom, inverted with its open end downwards into the cistern of water.
This vessel is always made of sheet-iron plates rivetted together
air-tight, and was suspended by a chain or chains, passing over wheels,
supported by a frame work.

If the common air be allowed to escape from the inner vessel, when its
open end is under the edge of the water in the outer cistern, it will
freely descend, and water will occupy the place of the air; but if the
avenue of the escape be stopped, and air be made to pass through the
water, the suspended inverted vessel will rise to make room for the air.
And, again, if the suspended vessel be counterpoised by a weight, so as
to allow it to be a little heavier than the quantity of water which it
displaces, it will descend, if, the entering gas be withdrawn through an
outlet made in the vessel to permit the gas to escape. But if the outlet
be stopped, and air again be admitted under the vessel, it will rise
again. The apparatus, therefore, is not only a reservoir for storing up
the gas introduced into it, but serves to expel the gas which it
contains, when required, into the pipes and mains connected with this

According to this construction of the apparatus the interior inverted
vessel forms strictly what is termed the gas holder. It is suspended as
already stated in the outer cistern, by a chain or chains, passing over
pullies, supported by blocks and frame work, and to the chain there is
affixed a counterpoise balance, of such a relative weight, as to allow
the gas holder a slow descent into the water, in order to propel the gas
into the mains or vessel destined to receive it, with a very small and
uniform weight.

It will be obvious, that when a gas holder of this construction becomes
immersed in the water, it loses as much of its weight as is equal to the
bulk of water which it displaces, and hence to render its descent
uniform, and to preserve the gas within, of an invariable density, at
any degree of immersion, a greater counterpoise is required as the gas
holder rises out of the water.

Among various methods which have been adopted to attain this object, the
ends of the chains by which the gas holder is suspended, have been
fastened in separate grooves, in the edge of a large wheel or pulley, of
such a diameter, that the gas holder rises to its full height, before
the wheel makes one revolution.

In another groove in the edge of the same wheel, was fixed the end of
another chain, to which a balance weight was suspended. This weight was
made nearly equal to the weight of the gas holder. To equalize the
density of the gas within the gas holder, at any degree of immersion of
the vessel, the weight chain was made to pass over a wheel, furnished
with a spiral groove, so as to make the radii of the wheel, change
reciprocally with the relative weight of the gas holder, and
consequently to render the pressure of the gas holder constant and

Another and more elegant method of obtaining an uniform elasticity of
the gas within the gas holder, and which has been more generally
adopted, consists in passing the chain or chains by which the gas holder
is suspended over a pully or wheels, and making the weight of that
portion of the chain, which is equal to the depth of the gas holder, or
that part of it which becomes immersed into the water, equal to one
half of the weight of the specific gravity of the gas holder.

It is obvious that before the purified gas can be admitted into the gas
holder, the vessel must be allowed to descend to the bottom of the
exterior cistern, in order to get rid of the common air which it
contains. This may be effected rapidly by opening the _man hole_ at the
top of the gas holder, to cause the vessel to descend completely into
the outer cistern filled with water. The man hole is then screwed up
again air-tight, and the machine is ready to receive the gas. It is
obvious that the operation of opening the man hole for letting out the
common air, requires only to be done once prior to the commencing of the
working of the apparatus.

_Gas Holder with Governor, or Regulating Gauge, lately brought into

It must be obvious that the gas holder, of which a description has been
given in the preceding page, requires a machinery at once ponderous and
very delicate, qualities not easily reconciled in the construction of
such a machine. It is necessary that the specific gravity apparatus, or
regulating chain, wheel work and balance weight, should be constructed
so correctly as never to suffer the gas within the vessel, to alter its
elasticity. The machinery requires an expensive framing for its support,
and independently of this, the gas holder must be inclosed in a
building, in order to protect it from the impulse of the wind, the
action of which would render the lights supplied from the apparatus
unsteady, as already stated. The expensive and cumbersome specific
gravity apparatus has been wholly superseded by an ingenious contrivance
called the regulator or governor. The action of this machine, for which
we are indebted to Mr. Clegg, is, that it regulates the density of the
gas prior to its entering into the mains, to any required degree,
whatever its density may be in the gas holder.

To accomplish this object, the apparatus through which the gas passes
into the mains, is provided with an aperture which is capable of being
enlarged or diminished by a very slight force. To effect this object the
gas is made to enter a small vessel, and then to pass through a
regulating aperture, the capacity of which becomes enlarged or
diminished by the velocity of the gas to a certain standard. If the
pressure of the gas in the gas holder becomes increased, the regulating
aperture through which the gas passes into the mains, becomes
diminished, in such a proportion, that the velocity with which the gas
issues into the mains, remains constant and uniform. And on the other
hand, if the pressure of the gas in the gas holder becomes diminished,
the regulating aperture of the governor becomes enlarged to effect the
intended regulation.

The following is a concise description of the manner in which this
instrument is constructed.

_A_, _B_, _C_, _D_, fig. 9, pl. III. is a hollow cylindrical vessel, or
the outer case of the machine. It is made of sheet iron or copper,
japanned within and without, closed at the top and bottom. It is placed
between the gas holder and the mains, into which the gas is to be
conveyed. _a_, _x_, is a pipe which proceeds from the outer vessel and
branches upwards in the centre of the base of the outer vessel A, B, C,
D. It brings the purified gas into the governor. _b_, T, is the outlet
pipe which conveys the gas from the governor into the mains. It is
placed above the inlet pipe and communicates with the interior vessel.
G, H, a short projecting hollow cylinder, which proceeds downwards from
the centre of the base of the outer case of the machine A, B, C, D. _u_,
_x_, _y_, _z_, is the regulator, properly so called; it consists of a
small conical vessel, also made of sheet iron or copper, closed at the
top and open at bottom, japanned within and without. This vessel rises
and falls vertically in the outer cylindrical case. A, B, C, D, of the
machine, when the latter is filled with water. It is kept steady in its
motion by two slender guide rods, as shewn in the sketch.

Between the inlet pipe which conveys the gas into the governor, and the
outlet pipe which conveys the gas into the mains, is fixed horizontally
a partition plate, having a circular aperture in the centre. This plate
is seen between the letters _x_, T.

Through this orifice passes a perpendicular axis P, which is fixed at
the top in the centre of the regulator or interior floating vessel _u_,
_x_, _y_, _z_.

The interior extremity of the axis P, is furnished with a cone, having
its base downwards, and projecting beyond the pipe _a_, _x_, into the
short cylinder G, H. The base of this cone slightly exceeds the diameter
of the orifice _x_, T, so as to close up entirely, when the regulator is
raised to its greatest height in the outer vessel A, B, C, D. But when
the floating vessel _u_, _x_, _y_, _z_, descends in the outer vessel A,
B, C, the vertex of the adjusting cone P, is just entering the aperture.

The regulator is conical, and its form is in exact proportion to the
loss of the weight of water which it displaces; so that the gas conveyed
into it always retains an invariable density at whatever height the
regulator may be immersed in the water in the outer vessel. If the outer
vessel be filled with water up to the top of the central branch pipe,
the interior vessel will float, and the water will stand in the outer
vessel at the same height as in the inside of the regulator; hence the
density of the gas within will be the same as the outer air. But the
density of the gas in the regulator may be increased at pleasure by
applying a weight to the top of the regulator, the water will then stand
higher on the outside of the regulator than within, and this adjustment
will remain uniform, because the quantity of matter of the regulator is
in the ratio of its specific gravity or loss of weight as it becomes
immersed in the water.

Let us suppose that the pipe above the partition plate be connected with
a main, and that the outlet pipe below the partition plate be connected
with a gas holder supplying gas into the machine; it will be evident
that if the density of the gas in the inlet pipe becomes by any means
increased, a greater quantity of gas must pass betwixt the sides of the
adjusting cone and the aperture in the partition plate, the consequence
of which will be that the floating regulator will rise, and therefore
contract the area of the partition plate. And if, on the contrary, the
gas in the inlet pipe decreases in density the regulator will descend,
so that whatever density the gas may at any time assume in the gas
holders or mains, its density in the floating vessel _u_, _x_, _y_, _z_,
will remain uniform, and consequently the velocity of the gas passing
into the mains will be regular.

For when the aperture of the partition plate would admit more gas than
what is necessary for the density of the gas in the mains, the floating
regulator rises, and by that means raises the adjusting cone to diminish
the aperture in the partition plate, and when, on the contrary, the
aperture does not allow a sufficient quantity of gas to come from the
gas holders, the gas passes out of the regulator into the mains, and in
so doing the regulator descends, and consequently the adjusting cone
increases the opening to admit the requisite gas into the mains.

The further application of this machine, for regulating the height of
the gas flames issuing from burners or lamps of different kinds will be
shewn hereafter.

_Gas Holder with Governor or Regulating Guage at the Gas Works Chester._

Fig. 7, plate VI., exhibits a perpendicular section of the gas holder at
Chester. A, A, are wooden beams or pillars fixed into sockets or shafts
constructed on the outside of the brick-work, and descending as seen in
the design to the depth of the tank. There are four of these pillars,
three only are seen in the section. B, B, are round iron guide rods
rendered steady by stays at the upper extremity of the rods.

To the upper and lower edges of the gas holder are fastened eye bolts,
C, C, through which the guide rods, B, B, are inserted, so that the gas
holder must move steadily and firmly. D, E, are the inlet and outlet
pipes which convey the gas into and out of the gas holder.

F, F, are diagonal stays for supporting the roof of the gas holder,
which has a slope of ten feet from the centre to the circumference. G,
is the wooden curb at the lower margin of the machine.

This gas holder is circular. It measures forty-eight feet in diameter,
and thirteen feet in height; its weight is eight tons.

The regulator adapted to this gas holder, measures three feet across its
base, and its height is three feet three inches. The base of the
regulating cone is four inches, and its length two feet. The machine is
made of sheet iron japanned within and without.

_Gas Holder with Governor or Regulating Guage at the Birmingham Gas

The construction of this gas holder, as exhibited plate V., fig. 2,
shows a perpendicular section, and fig. 3, a plan of the machine; _a_,
_a_, _a_, _a_, fig. 3, are upright pillars, two of which B, B, are seen
in the section, fig. 2.

In the centre of the gas holder is fixed a pipe, which allows the gas
holder to slide on the central guide rod G, made fast at the bottom of
the cistern, and at the top of the cross framing. C, C, are diagonal
stays; D, the inlet pipe which conveys the gas into the gas holder E;
the outlet pipe F, the wooden curb.

The capacity of this gas holder is 30,000 cubic feet; its regulator is
precisely similar to that before described. The weight of the gas
holder, exclusive of the wooden curbs at top and bottom, is between
eight and nine tons.[39]

  [39] The gas holder without specific gravity apparatus, at the Bristol
  Gas Works, is constructed on a similar principle. Its capacity is
  43,000 cubic feet. Its regulator is like those already described.

The gas holder thus disencumbered of its specific gravity apparatus,
requires no building to enclose it, it may be erected in the open air,
for the machine cannot suffer from the rain or snow falling upon it, nor
can the action of the wind render the lights unsteady.

The saving which has been effected by these improvements is very great.
A gas holder without balance weight and specific gravity apparatus, with
its governor, may be erected complete for action, for little more than
half the cost that would be required for the erection of an apparatus of
the same capacity constructed on the old plan.

The cheapest house constructed of sheet iron to surround a circular gas
holder of 15,000 cubic feet capacity, supposing the surface of its
cistern or tank to be level with the ground, costs no less than £. 320.
The balance weights and chains £. 60, and the cast-iron framing for
supporting the specific gravity machinery £. 150.

The cost of a gas holder of the before-mentioned capacity, will be £.
300, and a cast-iron tank for it, £. 800.--If the tank be constructed of
brick-work, it will cost about £. 500, and if of wood (an iron-bound
vat,) it will cost £. 600.

A governor or regulating guage adapted to a gas holder of from 10,000 to
40,000 cubic feet capacity, costs £. 50. In the construction of the gas
holders, as hitherto described, it is always advisable when the
situation will admit it, that the diameter to the height of the machine
should be in the proportion as three to two. If these dimensions be
observed, and the gas holder is not burdened by iron stays, it will not
displace a column of water more than one inch and a half in height. And
by adapting to the machine, a governor or regulating guage, a
considerable saving will be effected. The gas holder may then be
constructed as shown fig. 7, plate VI., or fig. 2, plate V. A circular
gas holder of 30,000 cubic feet capacity, if properly constructed,
weighs no more than eight or nine tons, including its wooden curb at its
lowest extremity, and its diagonal stays.[40]

  [40] Mr. Lee of Manchester supplies his house, two miles distance from
  the manufactory, by means of a portable gas holder.[41] A small
  carriage upon springs conveys two square close gas holders made of
  wrought iron plates, and each containing fifty cubic feet of perfectly
  purified gas, equivalent together to about six pounds of tallow. Each
  gas holder weighs about 160 pounds; and has a valve at the bottom,
  which is opened by the upright main pipe, the moment the gas holder is
  immersed in the pit. The strength of one man is found sufficient for
  the labour of removing the gas holder from the carriage to its place.

  [41] Henry’s Experiments on the Gas from Coal, in the Memoirs of the
  Manchester Literary and Philosophical Society, 1819.

The roof of the machine ought to be constructed of thicker sheet iron
than those forming its sides. The only object of the balance weight, is
to counterpoise the weight of the chain of the gas holder of the old
construction, so that when the gas holder is wholly immersed in the
cistern, the chain and balance weight are in equilibrium, deducting the
required pressure with which the gas holder is intended to act. And this
ought never to exceed from half an inch to an inch perpendicular _head_
of water.

The sheet iron best adapted for constructing gas holders, is that known
in commerce as No. 16, wire guage.[42] Gas holders made of plates of
iron of this kind, have now been in use for upwards of nine years, and
are not in the least injured or decayed. Self-interested views may
sometimes lead unprincipled workmen to make use of sheet iron plates of
a much greater thickness, but experience has sufficiently shown that any
greater thickness than what has been specified is wholly unnecessary,
and only serves as a drawback to the facility of the general operation.

  [42] A superficial foot weighs three pounds.

_Revolving Gas Holder at the Westminster Gas Works._

The revolving gas holder is an ingenious contrivance invented by Mr.
Clegg, for storing large quantities of gas. A gas holder of this
construction may be erected with advantage in situations where the
nature of the ground will not admit of a deep cistern either above or
below the ground being constructed, without an enormous expence.

The base which it occupies is no larger than what would be required for
a gas holder of equal capacity, built on the plan of the gas holders of
which descriptions have been just given.

It regulates its own specific gravity. And though more expensive in the
construction, yet as it does not require a deep cistern, like the
machines already described, it can be erected at the same cost. The
revolving gas holder is exhibited, fig. 8, plate VI. Its capacity is
15,000 cubic feet; it weighs 12 tons. Plate I., (on the title page,)
exhibits a perpendicular section of the gas holder.

On inspecting fig. 8, plate VI., it will be seen that this machine is
the segment of a hollow cylinder, or broad wheel, formed by two
concentric cylindric surfaces of 250° each, revolving upon an horizontal
axis, and supported upon a wooden frame or truss, in a brick cistern, I,
K, L.

The extremity C, D, fig. 8, plate VI., or C, plate I., of the segment of
the cylinder, is open, and the other extremity A, is closed. E, is a
balance pipe, which connects the closed with the open extremity of the

This pipe is made of such a weight as to counterpoise the interval
between the open and closed end of the gas holder, so that the machine
may move in a segment of a circle equally, in whatever position it may
happen to be placed, and hence the gas will be discharged from the gas
holder with an uniform velocity.

The balance pipe E, is closed at the part where the letter E is placed;
H, is a straight pipe, which forms the communication between the
balance pipe E, and the horizontal axis upon which the machine moves.
This axis is hollow: it is supported by stays and braces, as shown in
the design on the title page. The cistern in which the gas holder moves
is 7¹⁄₂ feet deep. It must be evident that the gas being conveyed into
the open end of the hollow axis, it will pass through the pipe H, into
the balance pipe E, and this being stopped up near E, the gas will
proceed into the closed end of the gas holder. The operation will
therefore be as follows:

Let us suppose the closed extremity of the machine to be at the surface
of the water in the cistern, and the gas flowing through the axis as
described, the extremity of the machine will begin to fill, and
consequently to ascend; the gas holder will therefore continue to move
upon its axis until the open end C, D, fig. 8, plate VI., or C, plate
I., comes nearly to the surface of the water, and when the gas is
required to be discharged, it will return through the same channel by
which it entered. A sufficient pressure is given to this gas holder for
discharging the gas at the velocity required, by means of a weight
suspended to one extremity of a chain, passing over a pulley, whilst
the other end is fastened into the groove of a small circle attached to
the stays of the machine, as shown in the designs. The circle is
graduated to express the capacity of the machine. Thus any degree of
pressure may be given to the gas, and the gas holder will retrograde in
an arc describing 270° of a circle, as the gas becomes discharged, until
the end A, again arrives at the surface of the water.

The small curved pipe T, plate I., serves to let the common air escape
out of the angular extremity of the machine, whilst filling with gas,
when the margin of this part of the machine becomes immersed in the
water, and to let the common air enter again, when the gas holder is
discharging its contents.

S, plate I., is a friction sector, upon which the axis of the machine
revolves. The advantage of this contrivance is, that the friction is
very much diminished. The length of the friction sector is eight feet,
the diameter of the gudgeon or axis four inches; therefore the space
described by its outer circumference and its centre is in the proportion
of 96 to 4.

_Rule for finding the capacity of a Revolving Gas Holder of given

To find the capacity of a revolving gas holder, of given dimensions,
take the area of the whole diameter, then the area of the inner
cylinder, multiply the difference by the length, and from this deduct

_Collapsing Gas Holder._

The collapsing gas holder is a still farther improvement by Mr. Clegg,
on this part of the gas light apparatus, and certainly of all the
contrivances which have been invented for collecting and storing up
large quantities of gas, this machine must be pronounced to be by far
the most simple, economical, and efficient. The striking advantage of
the revolving gas holder which we have just been describing is, that it
enables the dimensions of the tank to be very much diminished, where the
nature of the ground will not admit of a cistern of great depth being
sunk, except at an extraordinary expence; but the still superior feature
of the collapsing gas holder which we now come to describe, is, that it
may be constructed of any required capacity, and adapted to a tank or
cistern of such diminished depth, as scarcely to deserve that name. It
requires a sheet of water no more than 18 inches in height, so that it
may be constructed in or upon ground of all descriptions, not only with
every possible facility, but at an immense saving of expence.

Fig. 1, plate VII., exhibits a perspective view of this gas holder. It
is composed of[43] two quadrangular side plates joined to two end
plates, meeting together at top in a ridge, like the roof of a house.
The side and end plates are united together by air tight hinges, and the
joints are covered with leather, to allow the side plates to fold
together and to open in the manner of a portfolio. The bottom edges of
the gas holder are immersed in a shallow cistern of water, to confine
the gas. By the opening out or closing up of the sides and ends of the
gas holder, its internal capacity is enlarged or diminished, and this
variation of capacity is effected without a deep tank of water to
immerse the whole gas holder in, as required in the ordinary
construction of rising and falling gas holders. The collapsing gas
holder requires therefore only a very shallow trough of water to immerse
the bottom edges of the gas holder to prevent the escape of the gas
introduced into it. The lower edges of the gas holder which dip in water
are made to move in an horizontal plane or nearly so, when they are
opened, so that they dip very little deeper in the water when shut or
folded together, than when opened out.

  [43] From Mr. Clegg’s specification--the same letters of reference
  indicate the same parts in all the designs.

For this purpose the top or ridge joints which unite the two sides of
the gas holder, are slightly raised up when the sides close or approach
together, or slightly depressed when the sides open out or recede from
each other. To guide the whole gas holder in this movement, two
perpendicular rods rise from the bottom of the shallow tank which pass
through sockets in the ridge joints at the upper part of the gas holder.
These sockets are secured by collars of leather round the shafts or
rods, to prevent the escape of the gas, and they are braced by chains
proceeding from their upper extremities and fastened at the ground on
each side of the tank.

The weight of the gas holder is balanced by levers bent in the form of
the letter L, and placed inside of the gas holder. These levers move on
centre pins fixed at the bottom of the shallow trough, which pass
through the angles of the L levers. The perpendicular arms of the levers
are jointed at their upper extremities to the sides of the gas holder,
nearly in the middle. At the ends of the horizontal arms of the L
levers, are weights to counterbalance the weights of the gas holder, and
both sides of the gasholder are provided with these kind of levers,
which at the same time that they balance its weight cause the ridge
joint of the machine to rise and fall, as before described, so that the
under edges of the gasholder, which are immersed in the water to confine
the gas, must move in an horizontal plane instead of describing an arc
of a circle as they would do if the ridge joint was a fixed centre of

When the gas holder is closed the perpendicular arms of the levers stand
nearly in a perpendicular position, but when the gas holder is opened
out the levers become inclined. And as they move upon a fixed fulcrum at
their lower extremities, and are jointed to the sides of the gas holder
at their upper extremities, they allow the whole of the gas holder to
descend gradually upon the guide rods, nearly in the same degree as the
lower edges would rise up if the ridge joint was stable, and if the
sides described an arc of a circle.

It is obvious, however, that the latter movement is not very essential,
but it is convenient and necessary to make a very inconsiderable depth
of water in the trough or tank serve the purpose it is intended. It may
be also observed that the sides of the collapsing gas holder may be made
to unfold or open on a fixed ridge point as a centre of motion, but it
will then require a considerable depth of water in the tank to keep the
lower edges of the sides and ends of the machine always beneath the
surface of the water, because the sides of the gas holder then describe
an arc of a circle when they are open. Fig. 1, plate VII., is a
perspective view of the apparatus, as it appears when partly filled with
gas. Fig. 2, plate VI., exhibits a perpendicular longitudinal section
made through the middle of the gas holder and tank; fig. 3, plate VI.,
represents a transverse section; fig. 4, plate VI., is an end view of
the machine, and fig. 5, exhibits an horizontal plan or section of part
of the gas holder, or one of its ends, to show how the end plates are
jointed together, and the leather applied to prevent the escape of the

A, fig. 2, is the inlet pipe which conveys the gas into the machine, it
rises up perpendicularly through the water in the tank, high enough to
prevent the water entering it. B, is the exit pipe for discharging the
gas into the mains from the gas holder. It rises up nearly to the top of
the machine. C, C, are the guide rods, they are firmly fixed at their
lower extremities into a cast-iron framing D, D, beneath the bottom of
the tank. The upper ends of these rods are kept steady by chains E, E,
fig. 3, and fig. 4, descending on each side of the gas holder, and
fastened at bottom to D, D, part of the same iron framing. F, G, K, K,
are the balance (or L) levers which suspend or bear up the gas holders;
they move on fixed centre pins supported in pieces _a_, _a_, fig. 2, and
3, of the framing D. The upper end of the perpendicular arms are jointed
to the iron bars H, H, H, see fig. 2, which are riveted to the side
plates of the gas holder; they are united by knuckle joints W, fig. 6,
which allow the sides of the machine to approach each other till they
come together. The arms _i_, _i_, of the bent levers F, G, K, K, fig. 4,
are placed nearly at right angles to the other arms F, G, fig. 3, and
the extremities of the arms _i_, _i_, are loaded with counterpoise
weights K, K, which always tend to bring the arms F, G, into a vertical
position, and consequently to close up the sides of the gas holder, in
order to expel the gas through the exit pipe B, fig. 2.

Three pairs of the above mentioned L levers are represented in fig. 2,
in the length of the gas holder to support it in different parts and to
prevent it altering its figure. The weight that must be used is
according to the magnitude of the machine. The pairs of levers F, G, K,
K, fig. 3, are placed side by side on the same centre pins, and cross
each other. K, K, are counterpoises at the ends of the arms _i_, _i_,
they are long pieces of iron extending from one lever K, to the next
lever. The tank is furnished at the bottom with a recess, as seen in
fig. 3, and 4, to allow the arms _i_, _i_, and counterpoises K, K, to
descend beneath the edges of the gas holder. In the course of the
movement of the machine, the sides of the gas holder are shorter at the
top or ridge joints than at the bottom edges, as seen in fig. 2, in
order that the under edges of the folding ends can move in an horizontal
plane. Each of the folding ends is made of two triangular plates,
connected together by an air tight joint, and each plate is again
jointed to its respective side plate, and they are made tight by
introducing a piece of leather or oil-cloth, or any other flexible
substance impervious to air in the angle at the joint.

Fig. 5, represents the end plates of the gas holder when nearly
extended, but when it is closed up, the two parts N, O, of the end
assume the position as shewn by dotted lines. L, M, fig. 5, shews how
the ends of the two side plates are turned outwards at _b_, to render
them stiff and firm. As all the flexible joints are made strong by
metallic joints or hinges, the leather has no stress to bear but only to
prevent the escape of the gas; R, R, fig. 2, are the collars of leather
to prevent the escape of the gas at the openings in the top or ridge
joint where the guide rods _c_, _c_, pass through.

The tank must be filled with water to such a level that the under edges
of the sides and ends of the gas holder will be a few inches immersed in
the water. The counterpoises K, K, fig. 3, tend to close the sides of
the machine together, and expel the gas from the gas holder through the
pipe B, fig. 2. The counterpoises are so adjusted in weight as to force
out the gas with the requisite pressure.

If more gas be introduced by the pipe A, it distends the sides of the
machine and moves them outwards upon the ridge joint. A man hole, as
seen at S, fig. 2, is made in each side of the gas holder, to give
entrance when any repairs are necessary, or to oil or examine the
joining leathers. It is scarcely necessary to add that the form and
dimensions of this gas holder, and the materials of which it can be made
may be varied without any deviation from its essential properties as
they have been now described. For instance, the ends of the gas holder
may be formed of more than two folding plates, united together, if it is
judged necessary, and the levers F, G, may be varied in number, form, or
proportion, provided they balance the weight of the sides and cause the
lower edges of the gas holder to move nearly in an horizontal plane. Or
the balance levers may be laid aside entirely, and the gas holder may be
suspended from the upper part of the guide rods C, C, without moving up
and down thereon. But in this case it will require more water in the
tank to keep the open end of the gas holder always immersed in the
water; the weight of the sides of the gas holder will then tend more to
bring them together and to expel the gas.

In proportion as the quantity of water sufficient for the tank of the
collapsing gas holder is less than that required for the tanks of other
gas holders, it is attended with this further advantage, that the water
can be let off or removed without any expence when repairs are
necessary. If the repairs indeed are trivial, they can be made without
letting off the water at all, the depth being no more than one foot. In
the case, on the contrary, of the gas holder, with or without specific
gravity apparatus, the quantity of water is so considerable, that the
means provided for carrying it off must always be attended with great
difficulty and expence; and yet it is a provision which is in all cases
indispensable, no matter however difficult or expensive, for no material
repair to the interior of the apparatus can be otherwise effected.

With regard to the best size of a gas holder adapted to a certain number
of retorts, it may be stated, that this machine should be of a
sufficient capacity to hold the whole quantity of gas that is required
for the supply of the lights during one night, exclusive of what may be
furnished by the retorts during that time.

_Rule for finding the capacity of a Collapsing Gas Holder of given

The bulk of gas which a collapsing gas holder of given dimensions will
contain, may be found, by multiplying the area of the triangle contained
between the side plates when at their greatest extent, and the surface
of the water, by the mean length of the side plate. For example, suppose
the base of the triangular end plate be 30 feet long, and 30 feet high,
and that the length of the side plate at the top be 40 feet, and at the
bottom 60 feet,

  30 × 15 = 450 area of end plate,
  450 × 50 = mean length of end plate,
  = 22,000 cubic feet capacity.[44]

  [44] A collapsing gas holder of 22,000 cubic feet capacity, costs
  about £. 800, it weighs eight tons; a collapsing gas holder containing
  15,000 cubic feet, which weighs seven tons, costs about £. 700, and a
  ditto containing 30,000 cubic feet costs about £. 1000. The depth of
  the cistern for either is one foot.

_Reciprocating Safety Valve._

It must be sufficiently obvious that when the gas holder is full, and
the distillation of the gas continues going on, that unless a provision
is made for conveying away the surplus gas, it must escape by bubbling
up from underneath the gas holder. And should the gas holder happen to
be enclosed within walls, the gas may by chance accumulate, so as to
give rise to serious accidents.

As a remedy for this evil the manufacturers of coal gas have until very
lately contented themselves with what is called a _safety tube_, adapted
to the gas holder, by which, all the superfluous gas was carried away
into the open air; or by leaving large apertures in the roof or upper
part of the building, for the ready escape of the gas. By either of
these devices the danger from the accumulation of waste gas, was in part
only avoided, and instances might be named where dangerous consequences
ensued from an accumulation of gas, in a confined atmosphere, in the
vicinity of the upper part of the gas holder.

In some instances, indeed, recourse was had to the establishment of a
communication between all the reservoirs and an auxiliary gas holder or
gas holders, by means of a pipe furnished with an hydraulic valve; but
this was an expensive arrangement which required personal
superintendance, and depended, of course, for its efficiency on the
integrity and good conduct of the servant employed.

Mr. Clegg has now, however, invented what has been termed the
Reciprocating Safety Valve, which has a self-acting operation, and by
which an exit for the surplus gas of any number of gas holders that may
be in action is provided to an unlimited extent. A communication is
established between all the gas holders and a waste pipe, which
communication opens or closes by the action of the gas, as occasion
requires, and which may be extended to any number of gas holders at a
trifling cost.

The apparatus has now been adopted at the greater number of gas light
establishments, and has been uniformly found most efficient in its
operation. Fig. 9, plate VI., presents a perpendicular section of the
apparatus; _h_, _h_, _h_, _h_, is a small vessel made of sheet iron,
about eighteen inches in diameter, and twenty inches deep, closed at top
and open at bottom. It is inverted into an outer air tight vessel, _i_,
_i_, _i_, _i_, of double the height and rather greater diameter, which
is filled with water to a certain height; D, is a pipe communicating
with the gas holders that are in action; this pipe branches upwards
through the bottom of the outer vessel, _i_, _i_, _i_, _i_, and reaches
a little above the surface of the water in the outer vessel. E, is a
small pipe, the upper extremity of which is sealed by means of an
inverted sheet iron cup G, the edge of which is submersed under the
surface of the water in the outer vessel, _i_, _i_, _i_, _i_. This pipe
conveys the waste gas into the upper part of any chimney.

For let us suppose that the gas holders become overcharged; the gas must
then acquire an increased density before the wooden curb of the gas
holder G, fig. 7, plate VI.,[45] at the lower extremity of the
overcharged gas holder can begin to rise out of the water. But when the
elasticity of the gas is thus far increasing, and before the curb can
wholly emerge out of the water, the small vessel _h_, _h_, _h_, _h_, of
the reciprocating safety valve, ascends, and consequently establishes a
communication between the overcharged gas holder and the pipe D, of the
reciprocating safety valve. The surplus gas thus passes into the waste
pipe E, E, which had been before sealed by the inverted cup G, and is
hence conveyed into the upper part of the chimney where it terminates,
so that no accumulation of gas can ever take place above, or in the
vicinity of any gas holder.

  [45] Every gas holder ought to have a wooden curb at the bottom.

It must be obvious on the other hand, that when the gas in any of the
gas holders has recovered its original density, the reciprocating safety
valve will again be closed by the descending of the cup G.


_Gas Metre, or Self-acting Guage, which measures and registers, in the
absence of the observer, the quantity of Gas produced in a given time,
from any given quantity of coal, or consumed during a given period, by
any number of burners or lamps._

For the invention of this machine we are indebted to the ingenuity and
talents of Mr. Clegg, and undoubtedly, of all the improvements with
which the new art of procuring light has been recently enriched, there
is none which has been attended with results more beneficial to the
interest both of the manufacturer and consumer of coal gas.

In this machine we see combined a standard or check on the conduct of
the workmen, which enables the manufacturer of coal gas to assure
himself of obtaining at all times the greatest possible produce from his
establishment; a measure by which he can deal the gas out to his
customers in whatever quantities they may require it, and an index which
registers the exact quantities furnished, and thus serves as an
infallible account of debtor and creditor between the seller and
purchaser of gas.

This machine, therefore, performs at once all the duties of an overseer,
meter, and book-keeper, and performs them all so much more effectually,
that its operation is not dependant on matters so uncertain as the care
or integrity of servants, but on unerring principles which are fixed and
incapable of any hidden misapplication.

The view in which this machine naturally demands our particular
attention is that in which as a standard of the work which ought to be
performed, it enables the manufacturer to make sure of obtaining the
greatest possible produce from his establishment.

The gas metre serves this purpose in the first place by enabling the
proprietors of gas works to know what is the utmost possible quantity of
gas which can economically be obtained from any given portion of coal,
with a given portion of fuel, in any given time.

It is necessary, in every gas light establishment, in order to know
whether as much gas is obtained as might and ought to be produced, that
it be previously ascertained by a series of experiments how much gas the
species of coal used at the works is capable, on an average, of
producing, and such data it is obvious, can only be obtained by means of
an apparatus, which, like this gas metre, shall take measure of the
quantities of gas supplied by the manufactory at all times, and under
all circumstances.

It may, perhaps, be imagined, that assays sufficient for that purpose
might be made by means of a few retorts, or small experimental
apparatus, or by noting down the quantity of gas produced at the works
during the time the valves which convey the gas into the street mains
are shut, and during which time the capacity of the gas holders may
afford a rule for ascertaining the quantity produced. But nothing can be
further from the truth; assays of this description to be practically
useful and to serve as a basis for the operations of a large
establishment, must be made on a scale of magnitude and be continued for
a considerable period of time as well as under every variety of

The quantity of gas obtained from any given quantity of coal, varies so
much with the degree of heat applied, and the circumstances under which
the decomposition of the coal is effected, that the solitary product of
any one period of time can afford no positive criterion for the product
of any other period. A correct general conclusion, in short, can only be
drawn from the result of experiments carried on uninterruptedly through
a succession of days and nights, and such a continuity of experiments
could, previous to the invention of the gas metre, only be affected by
means of two separate gas holders, one for measuring the gas as it is
produced, and the other for receiving the gas after it is thus measured,
in order to its being transferred into the mains. By the aid of a single
gas holder, an admeasurement could obviously be effected only during the
time the valves which transmit the gas into the street mains are shut,
and this, when the days are short, as in the winter season, the most
productive period of the whole year, is only about eight hours out of
the twenty-four, leaving nearly two-thirds of each day, during which, no
account could be taken of the quantity of gas produced at the works.

It deserves further to be observed, that when two gas holders are
employed, the utmost that can be effected by them, is the admeasurement
of the gas produced, while the distinguishing feature of the metre is,
that it not only measures, but by its own action registers the quantity
of gas produced, or expended, in any given time.

Nor does the whole merit of this machine, in an economical point of
view, consist in its thus furnishing the manufacturer with an infallible
criterion of the quantity of gas which ought at all times to be
produced; for, in the second place, it enables him by the several
experiments which have supplied that criterion, to ascertain at what
least possible expenditure of fuel, and in what space of time the
greatest possible quantity of gas can be produced.

The advantage of the gas metre, in these additional respects, will be
sufficiently demonstrated by attending for a moment to the situation of
the manufacturer of coal gas, when without any such protecting register.
Suppose, for example, that the manufacturer desires to know whether his
workmen have made during a given time, (say during the night), the
quantity of gas which they ought to have produced from a given quantity
of coal, or whether they have consumed no greater proportion of fuel for
its production than was absolutely necessary. He may, upon examination,
find all the retorts in an excellent working state, but whether they
have been so during the whole of the night, or whether the requisite
quantity of gas has been really produced during the time that the valves
which convey the gas into the mains have been open, is to him a matter
of uncertainty. The workman may, as has been too often the case, have
neglected the fire during the night, and on every such occasion, in
order to bring back again the retorts to a proper working state, as well
as to redeem the time lost, he may have urged the heat to a degree of
intensity much exceeding the temperature best suited for the most
economical production of the gas. And however injurious such irregular
modes of operating may be for the master’s interest they are altogether
shrouded from his observation. It deserves also to be noticed that the
loss occasioned by this irregularity of operating is not merely a loss
of fuel, for in consequence of it the retorts, (particularly if
cast-iron retorts of the usual forms,) are liable to more injury in one
day than they would be during a whole week, if properly attended.

When the proprietor of the establishment, on the contrary, has recourse
to the gas metre, not one of all these evils can occur without being
liable to certain and instant detection. From the data which preceding
experiments on the productiveness of the species of coal used at the
establishment have furnished, the overseer of the works is always
enabled to determine, from the portion of coal he finds used, how much
gas ought to have been manufactured during any space of time that has
elapsed, and also the portion of carbonizing fuel which was necessary
for the production of that quantity of gas; and comparing these data
with the quantity of gas which the index of the gas metre announces has
been produced, he is enabled to determine by mere inspection, in an
unerring manner, whether the workman has acted with that sedulous
attention to his duty which the economy of the establishment demands.

The many important advantages in short which the manufacturer of coal
gas derives from this machine, considered _as a standard or check on the
conduct of the workmen_, may be summed up in this--that while, without
the aid of the gas metre, no establishment can be possibly more exposed
to suffer from the ignorance of managers or the want of fidelity in
servants, than a gas manufactory, there is none which is more
independent of either than a gas manufactory, possessed of this
important apparatus. Nor can the amount of that possible loss be
regarded as otherwise than extremely serious, when attention is paid to
the difference in profit and loss between conducting the process of
manufacturing coal gas on a system founded on the deductions of
experience, and an assiduous attention to keeping up a regularly
sustained temperature; and conducting the process on a system of random
calculation and irregular working,--a difference, which as appears from
the details already laid before the reader, amounts in respect to the
quantity of gas produced, to from fifty to one hundred per cent.; in
respect to the waste of machinery, to upwards of eighty per cent.; and
in respect to the consumption of fuel and time to a sum in the ratio of
the loss experienced under both these other heads.

The Second General Point of View in which the gas metre claims our
attention, is, its excellence as a standard of fair dealing between the
seller and consumer of gas, by enabling the former to supply the gas in
whatever quantities it may be required, and serving, at the same time,
as a self-acting register of the quantities furnished. It is for this
purpose merely necessary to connect the gas metre with the pipe of
supply, which conveys the gas to any burner, or number of burners, or
lamps, and the index of the instrument will regularly announce the
precise quantity of gas which has passed through the machine during any
period of time, from one day to a number of years, without requiring any
particular sort of care whatever. Every person must have noticed how
shamefully many individuals disregard the terms on which they have
contracted for a supply of gas, some by means of the excessive flame
they keep up, and others suffering the lights to burn hours beyond the
time stipulated and contracted with the gas light company which supplies
them. The latter have officers, it is true, whose duty it is to check
such abuses as far as is in their power, but having no right of access
to the premises of individuals, their vigilance can only extend to shops
and places open to public view and of general access; and to these, of
course, but occasionally. In short in every place where gas is supplied
on contracts to pay for burning it a limited time, by means of certain
sized burners or lamps, instead of according to the quantity actually
furnished, the seller must always be in a greater or less degree, and in
some cases wholly dependent on the care and honesty of the purchaser for
the protection of his commodity from waste and depredation. But when on
the contrary the seller possesses, as he now does, by means of the gas
metre, an infallible check of the exact quantity of gas consumed in a
certain time, and the purchaser is bound to pay for as much as he uses,
the former is relieved from every apprehension or chance of being
defrauded, and the latter is furnished with the same motives for
economizing gas as he would have for economizing oil and candles.

The manufacturer is certain of obtaining what he has a just right to,
value for the whole quantity of gas supplied, and the consumer is
assured that if he wastes the gas unnecessarily, he must as he ought,
pay the price of his own carelessness or profusion. Equal justice is
done both to the consumer and seller, and the public at large are at the
same time most materially benefited, in as much as they are saved from
paying for the expence of that waste of gas by a few, which from the
former impossibility of tracing it to the offending parties, was
necessarily added to the whole cost of the gas, and equally partitioned
upon all the individuals who made use of it. The waste being now
transferred to those who occasioning the waste and ought alone in
justice to bear it, the price of the gas to the equitable and honest
consumer, is thus reduced to an equitable and correct measure of value.

The benefits of this invention have a yet wider range; not only does it
secure full value for the whole of the gas manufactured, but it tends to
make the gas a greatly more marketable article. For in the system of
charging for the supply of gas by the year, half year, or quarter, and
at one common rate, many individuals who are only occasionally in want
of gas lights, or whose demand is irregular and uncertain, such as the
proprietors of public rooms, theatres, &c. are debarred of availing
themselves of this kind of illumination, except at an expence quite
disproportioned to what other more regular customers pay, and out of all
proportion of the value of the quantity of gas consumed by them. The gas
light under such circumstances is not as it ought to be, a light for
all. It is not as oil and candle are, a benefit which every one may
obtain who is in need of it, and in such quantities as may best suit his
means and convenience. One of the capital advantages, of the gas metre,
however, is, that it makes gas a substitute for oil and candles,
applicable under all circumstances, and that it enables the manufacturer
without the least prejudice or chance of prejudice to his interest, to
supply gas in whatever quantities it may be demanded, and at a fair
proportioned price.

In speaking thus of the influence which the gas metre must have in
attending the beneficial application of the new lights, we are not
unaware that situations may present itself where the action of the metre
might be impeded from the want of a sufficient pressure of the gas in
the pipe of supply connected with it. But this can never be the case
except where the pressure of the gas in the pipe of supply is so low as
three-eighths of an inch of a column of water, and in all such cases it
is only necessary to give a greater capacity to the wheel of the
machine, than would be necessary under other circumstances, and this
will at once make up for the inferiority of pressure. In point of fact,
therefore, no situation can occur, where the application of the machine
may not be rendered available.[46]

  [46] See directions to workmen, for adapting gas metres, p. 229.

Nor do the various advantages which have now been detailed, form all the
good that this important machine is capable of furnishing. The gas metre
furnishes at its axis a power which has been ingeniously applied to put
in motion the shaft of the lime machine, employed for purifying the gas,
see fig. 3, plate VII.[47] The importance of a power thus certain in its
operation, and obtained free of expence, must at once be obvious, when
it is considered that upon whatever plan the purifying apparatus or lime
machine may be constructed, it is absolutely essential, that its
contents be kept constantly in motion, in order to produce the desired
effect upon the crude gas, which would otherwise pass away in an impure

  [47] The upper axis communicates with the agitating shaft of the lime
  machine, and the lower axis is a continuation of the shaft of the gas
  metre. The two pullies are connected by a strap.

When the charge of keeping the agitating shaft of the lime machine in
action, is intrusted to a workman, there is no positive security against
his occasionally neglecting his duty, whereas by applying the gas metre
to that purpose, the manufacturer is assured beyond the possibility of
deception, that when gas is produced, that gas is as certainly purified,
and a saving is effected in point of labour of the expence of two men,
one during the day, and one during the night.

_Description of the Gas Metre at the Royal Mint Gas Works._

Fig. 4, plate II., represents a perpendicular section of the gas metre.
It is placed between the purifying apparatus or lime machine, and the
gas holder fig. 8, plate III., exhibits a front elevation; fig. 1, plate
III., a perspective view, and fig. 6, plate III., a transverse section
of the machine.

It consists of a hollow wheel or cylinder, made of thin iron plate,
revolving upon an horizontal axis, in the manner of a grindstone; this
wheel is enclosed in a cast iron air tight case containing water.

The cylinder or wheel, is composed of two circular channels, 1 and 2,
fig. 4, plate II., concentric to each other. The larger or outer channel
1, is divided into three equal compartments, by partition plates, marked
_a_, as shewn in the design. The compartments are provided with
hydraulic ducts or valves, made at the upper part of every partition
plate _a_, _a_, _a_, and by means of them a communication is formed
between the larger concentric channel 1, and the outer case in which the
wheel revolves.

Similar valves are also placed at the foot of each partition plate, they
are seen near the letters _a_, _a_, _a_, and by this means, a
communication is established, between each compartment or chamber of the
larger concentric channel 1, and the smaller interior circle 2, of the

On inspecting the design, it will be seen that the valves are situated
in opposite directions to each other, hence there can be no
communication either between the inner smaller concentric channel 2, and
the larger compartment of the wheel 1, nor between the latter
compartment, and the exterior case, in which the wheel revolves, except,
through the valves _a_, _a_, _a_, which form the communicating ducts. It
will be seen also, that these valves are carried from one chamber of the
machine into another, but in opposite directions; the entry into one
chamber, being in the opposite direction to the hydraulic duct, placed
in the other chamber.

From these particulars the action of the machine will be obvious.

Let us suppose that the outer case (which is marked in the sketch by a
black tint,) in which the wheel revolves, be filled with water, to about
an inch above the axis of the wheel, and that gas is conveyed into the
interior small channel, by a pipe, passing along the axis, so as to
allow the wheel to turn freely round, and that the pipe is turned up at
right angles in the inner chamber, and projects a little way above the
surface of the water, as shewn in the design. The gas then must enter
into the interior chamber of the wheel above the surface of the water,
and must press against the adjacent partition; it will therefore cause
the wheel to turn round, and in consequence of this motion, the next
partition plate will press the gas against the surface of the water, and
cause it to pass through the hydraulic opening, in an equal quantity to
that, which is introduced into the exterior chamber.

This alternate filling, and discharging, of the contents of each
chamber, will take place once during every revolution of the wheel, and
hence the number of times each particular chamber has been filled, and
emptied of gas, may be known.

In fact this machine performs the office of three revolving gas holders,
fixed on an horizontal axis, and moving in a cistern, which is the outer
case of the machine. One gas holder, or one compartment of the machine,
is always in the act of becoming filled with gas, another is emptying
its contents into the outer case, from which it passes into the
reservoir, where it is to be stored up, or to the lamps, where it is to
be burned, and the third compartment is stationary, or in an
equilibrium. The wheel in any situation will therefore always have one
of its receiving, and one of its discharging valves open, and
consequently it will revolve.

Now to ascertain the quantity of gas discharged by one revolution of the
wheel, we need only to know the capacity of the chambers, and add them
together. Let us for example suppose, that each chamber contains 576
cubic inches, then one revolution of the wheel, discharges a cubic foot
of gas. To register the total number of revolutions which the wheel
makes in a certain time, a train of wheel-work is connected with the
axis of the metre, see fig. 8, plate III.; it consists of a pinion
impelling a common train of wheel-work, composed of any number of
wheels. The pinion on the axis of one wheel, acts into the circumference
of the next wheel, and the circumference of the wheel being as ten to
one, it is obvious whilst the metre makes 100,000 revolutions, if the
series consists of six wheels, the last wheel of the series, will only
have made one revolution. Each axis of the wheels is provided with a
finger and dial plate, divided into ten parts, therefore any number of
revolutions may be read off at any time by inspection betwixt 10,000,000
and one.

The velocity with which the metre acts, is of course in proportion to
the quantity of gas passing through it. Thus suppose there is a burner
or gas lamp connected with the machine, of one foot capacity lighted,
which consumes four cubic feet of gas in an hour, the gas metre performs
four revolutions per hour, and so on for every number of burners or
lamps, not exceeding the number which the machine is calculated to

To render the construction of the gas metre more obvious, we have at
fig. 6, plate III., exhibited a transverse section of the machine; _a_,
is the outer case of the machine in which the wheel revolves. B, B, the
outer or larger concentric chamber, (marked 1, in fig. 4, plate II.) L,
the inner or smaller concentric chamber, (marked 2, in fig. 4, plate
II.) _d_, the index on the axis which passes through a stuffing box in
front of the machine. 5, 5, 5, 5, are stays or braces for supporting the
wheel; they are likewise seen in fig. 4, plate II. A, is the inlet pipe
for the gas to enter into the machine. The gas passes through the pipe
_h_, and from thence into the curved pipe _i_, into the interior chamber
L, of the metre. The pipe _h_, is surrounded by a second pipe K, which
has a small aperture at _x_, the office of which is, to act as a siphon,
in order to preserve the proper level of the water in the machine. The
water is poured into the machine, through the small funnel at the back
of the entrance pipe A. _y_, is a float, which stops the performance of
the metre altogether, if a fraudulent attempt should be made, to stop
the registering of the metre, by drawing off the water with which it is
charged. In fig. 1, plate III., _a_, is the inlet pipe; _b_, the outlet
pipe of the gas; and fig. 2, shows the interior chamber.

The registering wheel work, may be adapted to any part of the machine,
and the motion may be communicated by a mitre wheel, from the shaft of
the machine to the index.

The gas metre at the Royal Mint measures and registers 30,000 cubic feet
of gas every twenty-four hours.[48]

  [48] The gas metre at the Bristol gas works registers 60,000 cubic
  feet of gas every twenty-four hours. The metre at the Chester gas
  works registers 40,000 cubic feet every twenty-four hours.--One of the
  metres at the Birmingham gas works registers 40,000 cubic feet, and
  the other (now erecting) will register 100,000 cubic feet every
  twenty-four hours.

_Rule for calculating the weight, which a Gas Metre of given dimensions,
will raise to a given height, in a given time._

The following calculation will exemplify the power produced by a gas
metre constructed to register 60,000 cubic feet of gas, in a day. The
diameter of such a metre would be six feet, its depth three feet, and
the depth of its rim eighteen inches.

The section of the rim would therefore contain 648 square inches, and
supposing the pressure of the gas passing into the machine to be equal
to a column of water two inches high, its buoyant power would then be
equal to 1296 cubic inches of water, or forty pounds and a half weight.
The mean diameter of the metre is 4 feet 6 inches, which multiplied by
three, gives the perpendicular height that forty pounds and a half
weight, would be raised by each revolution of the metre. The number of
revolutions, in one hour which the metre makes, is 40, they would raise
forty pounds and a half, 540 feet high in one hour.

Such a power is more therefore than sufficient to keep in motion the
shaft of the lime machine.

_Gas Holder Valve,--Siphon, or Water Reservoir._

This name is given to the principal hydraulic valve, by means of which a
communication is established between the gas holder or gas holders, and
the principal pipe, leading to the mains.

Fig. 7, plate III., exhibits a section of this valve. It is composed of
an air tight box, A, A, A, A, containing a portion of tar, or water;
_d_, is the inlet pipe which communicates with the gas holder, B the
outlet pipe; which conveys the gas into the mains. C, C, is an inverted
cup, furnished with a sliding rod, passing through a stuffing box, so
that by means of the rod, the cup may be raised or depressed. For it is
obvious that a communication will be established between the inlet pipe
_d_, and the outlet _B_, when the cup is raised above the surface of the
tar or water in the box A; and that the communication will be cut off
when the cup is depressed into the tar. In the latter position the cup
is shewn in the design. The sliding rod which raises and depresses the
cup, passes through a frame E, E, affixed to the upper part of the box
A, and which serves as a guard for the rod, so that it may be locked by
means of a cutter passing through the sliding rod, and the frame of the

Fig. 3, plate III., exhibits a similar valve, which at the same time may
be used as a _water reservoir_, commonly called a _siphon_, for
collecting the water that may happen to accumulate in the mains, a
provision which it is essential should be made at the lowest place,
where two or more pipes incline towards each other. For it is obvious,
that if a fluid should happen to accumulate in the angular part, where
two descending pipes meet, to a height sufficient to fill the angular
point, the communication between the two pipes would be completely cut
off, so that the gas could not pass. _x_, _x_, _x_, _x_, fig. 3, is the
reservoir; A, the inlet pipe; B, the outlet pipe; _b_, a short cylinder
communicating with the exit pipe B, it is open at bottom and closed at
top. D, _d_, the hydraulic cup which, when raised by means of the
spindle _e_, closes the exit pipe B, by the open end of the cylinder
_b_, becoming immersed in the tar or water contained in the cup D, _d_.
The darts show the course of the gas when the valve is open: _f_ is a
small pipe furnished at top with a screw and covered with a cap; by
attaching a hand pump to this pipe, the superfluous portion of fluid
that may have accumulated in the reservoir, may be removed. _c_, _c_, is
the _equilibrium_ pipe, it connects the exit pipe B with the inlet pipe
A, when the stop-cock with which it is furnished is opened. This pipe
prevents the tar or water from being blown out of the hydraulic valves
that may be interposed between the different descending mains of a
district, as would otherwise happen, in consequence of the sudden
concussion that takes place when the main or gas holder valves are
opened. Because the gas in the mains, and the gas in the gas holders,
are not in equilibrium. But by means of the small pipe _c_, _c_, the
equilibrium is obtained when the stop-cock of the pipe _c_, _c_, is
opened, and this should always be done before the main or gas holder
valves are opened. For by neglecting this condition, the water or tar is
liable to be blown out of all the hydraulic valves, that may happen to
be interposed in the system of the pipes for conveying the gas, and
communications are thus opened, which were intended to be shut.


_Governor or Regulating Guage._

The governor or regulating guage, the construction of which has already
been detailed, page 171, we shall here consider as an instrument by
means of which the gas flames of lamps and burners are kept of one
steady and uniform magnitude.

The velocity of the gas in the mains and pipes of supply, is in the
first instance as various as there are differences in the altitude and
extent of the mains and pipes of supply. A main, at one place will
furnish with a certain pressure of gas, a flame one inch high, while at
a different altitude it will furnish a flame double that height.

If again the direction of the pipe has many turns or angles, and
contractions, the velocity of the gas will be different on that account,
than if it were direct and uniform. And if the pipe is of any great
length, and of an uniform bore, but unequally furnished with veins or
branch pipes at certain parts, the burners will be very unequally
supplied with gas, those which are near its head will be supplied with a
fuller stream of gas, than those which are situated towards its

And independent of these differences thus arising from diversity of
local positions, there will always be one grand variety in the velocity
of the gas, occasioned by the variety of periods during which lights are
required by different individuals supplied from the same main or system
of pipes, as for example: when a certain number of burners are to be
supplied, and it happens that one half of these burners are shut sooner
than the rest, then in consequence of this, the velocity of the gas in
the mains will be materially altered.

The inequality thus occasioned, may be seen particularly exemplified in
the case of houses situated in the vicinity of any large establishment,
such as either of the great theatres of the metropolis, and supplied
with gas from the same mains. While the theatres are open, the lights in
the adjacent houses are low and feeble, often too much so for the
necessary purposes of the consumer, but the moment the theatres are
shut, the great quantity of gas which they previously carried off, being
transferred to such of the private houses as continue to be lighted, the
gas flames at the latter are raised to an extravagant height, and burn
with an intensity which makes the gas light partake more of the
character of a nuisance than of a benefit.

It may be necessary for the better appreciation of the extent of this
nuisance to observe, that it does not arise merely from the excess of
light produced, but from the imperfect combustion of the gas, and hence
a disagreeable odour is produced. When the flame is suffered to rise
beyond the standard height, the combustion of the gas becomes imperfect,
part of the gas passes through the flame unburnt, and occasions the
source of the offensive odour alluded to, which the gas lights never
produce when the combustion of the gas is complete. The remedy for all
these inconveniences thus resulting from the various degrees of
velocity of the gas in the mains, is to be found in the instrument now
under description.

The effect of this machine, as already mentioned, is, that it causes the
gas to issue from the aperture of the burners or lamps with one uniform
velocity, whatever may be the variations which take place in the
pressure which urges the gas to pass through the pipes of supply. And
such is the efficiency of the operation of the machine, that it
regulates the flow of the gas through any burner, tube, or opening, with
a greater degree of exactness, than the centrifugal apparatus, regulates
the action of the steam engine.

The construction of the regulator to effect this purpose is precisely
similar to the apparatus already described, page 171. When applied for
regulating the magnitude of the gas flames, it is of course usually made
much smaller, of iron plates, japanned within and without. Fig. 4, plate
III., exhibits a perspective view of the machine; _a_, is the inlet
pipe, _b_, the outlet pipe; P, is the regulating cone, passing through
the regulating aperture _x_, T. The floating vessel _u_, _x_, _y_, _z_,
receives the gas introduced into the machine; A, B, C, D, is the outer
air tight case of the regulator.

_Directions to Workmen for fixing the Governor and Gas Metre._[49]

  [49] Copied from Messrs. Clegg’s and Crossley’s printed directions to
  workmen, for fixing governors and gas metres.

The governor must be fixed perpendicularly, so as to admit its floating
vessel _u_, _x_, _y_, _z_. Fig. 4, plate III., or fig. 9, plate III., to
be taken out of the outer case of the machine if occasion should require

The gas enters into the machine from the street mains at the lowest
branch _a_, and passes out of the machine by its highest branch _b_.

In connecting the pipes of supply, particular care must be taken that
the work is not _bound_, or the governor by any means rendered leaky. It
must be filled with water to the top of the central tube.

Examine the workmanship of the machine to see that it is perfect, and
that the regulating cone P, is firmly secured to the top of the
floating vessel and well centered. The floating vessels _u_, _x_, _y_,
_z_, should clear the sides of the outer case of the apparatus by a
quarter of an inch; and when sunk down, it should rest even upon the top
of the central pipe, which conducts the gas into, and out of, the
machine. The aperture in which the cone moves will then be at its widest
opening, and when the floating vessel _u_, _x_, _y_, _z_, has risen to
its highest elevation, the regulating aperture _x_, T, will be closed.

In this situation particular attention must be paid, that the regulating
cone does not stick or rub in any part, but that it descends freely.

To the lower extremity of the floating vessel _u_, _x_, _y_, _z_, may be
adapted an air vessel for the purpose of reducing the pressure of the

The governor must be so fixed, that the water which may condense in the
pipes leading to the burners shall drain back to the street mains, in
order that it may not accumulate in the machine so as to impede its
operations; for this purpose the gas pipes should have a fall of half an
inch in three or four feet.

When the locality of situation will not admit of the water that may
accumulate in the pipes falling back to the mains, its accumulation
within the governor above the proper level of the water is prevented by
an inverted siphon affixed to the machine, which allows the water to
drain off without any escape of the gas.

The governor must be firmly fixed to the nearest beam or wall, as the
least vibration will render the lights connected with it unsteady.

When a situation cannot be obtained sufficiently warm to prevent the
water from freezing, the machine must then be wrapped round with woollen
cloth, or any other bad conductor of heat. The cellar where the gas
enters the house, has generally been found the most convenient

For supplying any deficiency of water which the governor may require; a
small funnel with a curved tube is placed for this purpose at the top of
the governor. When the governor is filled to its proper height, the
water will begin to run out of the siphon.

The mode of regulating the height of the flames will be stated

Fig. 11, plate III., exhibits a portable governor or regulating guage,
combined with a gas metre in one case. A, is the inlet pipe which
conveys the gas into the machine, and B, is the pipe leading from the
governor to the lamps or burners. D, a label expressing the quantity of
gas discharged by one revolution of the wheel, and the number of lights
which the metre is capable of supplying when the pressure of the gas in
the inlet pipe is of a density sufficient to support a column of water
of half an inch in height.

In those situations where the pressure of the gas is equal in density to
support only a column of water one-quarter of an inch in height, a metre
of a larger capacity must be adopted for supplying the same number of
lights; and if the pressure of the gas be equal only to support a column
of water one-eighth of an inch in height, the capacity of the metre must
be still larger, and thus the capacity may be increased so as to equal
every pressure that may occur. The index which registers the number of
revolutions, and consequently the quantity of gas which passes through
the metre, is shut up in the projecting case, near H, furnished with a
lock and key.

Previously to the gas metre being filled with water, ascertain that the
regulating cone is screwed perfectly air tight into the top of the
floating vessel which receives the gas, and that the regulating aperture
in which the cone moves, together with its spindle and guide rods, work
perfectly free and without friction. Raise the floating vessel to its
highest elevation, thereby closing the regulating aperture suddenly with
the cone; in this situation it must not rub when turned and tried on
every side, but descend with the least friction.

The gas metre and regulator being thus examined and fixed, the machine
may be supplied with the requisite quantity of water in the following

Open the stop-cock which admits the gas into the machine; open also the
aperture E, which serves to show the pressure of the gas in the machine,
and likewise the opening G, which lets out the air whilst water is
poured in at the aperture H. The superfluous quantity of water will run
out by the siphon tube at K.

Pour water also into the governor until it runs out at the aperture at
M; and when this has been accomplished, till the gas metre with water
at the opening H, until it overflows at the aperture K, when the surface
of the water will appear at the cypher line on the scale board. The
apertures F, G, H, K, and M, may then be closed, and the machine is
ready for action.

Near to N, is an aperture communicating with the stuffing box in which
the axis of the machine moves, and through which it should occasionally
be supplied with a small portion of melted tallow.

To adjust the height of the gas flames of the burners, so that they be
all uniform, open the stop-cock which admits the gas into the metre, and
open also the stop-cocks of the burners, and as soon as the air has
become discharged by means of one or two revolutions of the metre, light
all the burners. Adjust the height of the flames in the first instance
by their stop-cocks, that they become all of an equal height, which
should be about double the diameter of the flame; if any of the flames
be too low when the stop-cock is fully open, a small weight must be
placed upon the top of the floating vessel of the regulator, sufficient
to produce the required flame at the burner, and then again adjust the
remaining lights by their stop-cocks as before stated; this being done,
the aperture to which each burner is screwed must be sufficiently
narrowed, that it will admit no more gas than is requisite for the
required height of the flame, when the stop-cock is fully open. The
diminution of the aperture of the stop-cock may be effected by a brass
plug fitted into it, with a hole in its centre, which must be gradually
widened with a drill until the flame has required the proper height. It
is recommended, instead of adding weight to the floating vessel of the
regulator, that the tubes which supply the gas be sufficiently capacious
to render the weight unnecessary.

The burners should also be examined from time to time. Observe that the
plugs, sockets, and every other part of the gas metre and regulator be
air tight, and that there be no escape of water or gas.

An escape of gas, either from the metre or from any of the tubes or
burners, will be discovered by looking at the index of the metre, as the
wheel cannot fail to move whenever there is an escape of gas, if the
stop-cock is open which supplies the gas to the metre. The place where
the gas escapes will be found in the usual way, either by the odour
which the gas produces, or by passing a lighted taper over the apertures
and connections of the metre, and along the tubes leading to the
burners, which will cause the gas to take fire at the place where the
leak happens to be.

The following remarks will assist the workmen in correcting any
irregularities which may occur in the lights connected with the

A diminution, or extinction of the lights, may be occasioned by a
deficiency of water in the gas metre or regulator; when this occurs the
necessary quantity of water must be supplied as before directed up to
the cypher line on the scale board E, of the metre, and opening the
aperture M, where it may be seen when the water has risen to the proper
height in the governor.

A diminution of light may also be occasioned by some obstruction or
contraction of the tubes which supply the gas, or by a diminution of the
pressure of the gas in the mains, to which the metre was originally

When the lights increase above their standard height, and are variable
with the changes in the pressure or velocity of the gas in the mains or
tubes of supply within the house or place, lighted, there is then reason
to believe that the governor is not performing, which may arise from the
following causes. Its floating vessel _u_, _x_, _y_, _z_, may have
become fast by the friction of the spindle or guide rod, requiring
cleaning, or by an accumulation of water in the air-vessel of the
floating vessel _u_, _x_, _y_, _z_. The water may be drained off at a
small plug by taking out the floating vessel. The same inconvenience
would arise from a diminution in the proper level of the water.

In order to ascertain that the governor performs correctly, observe at
the time of lighting or extinguishing any of the burners connected with
it, that its floating vessel rises and falls every time the stop-cock is
opened, and that the lights do not suffer any material change.

An instantaneous starting or dancing of the lights, is generally
occasioned by an accumulation of water in the tubes through which the
gas passes; if this should happen in the vicinity of the metre and
governor, it may be drained off at the aperture K. A provision for a
like purpose is also made at the bottom of the governor when detached
from the metre.

In order at any time to ascertain the pressure of the gas in the metre,
close the stop-cock which admits the gas, and open the aperture G and F,
which will shew the level of the water on the scale board E. This being
first observed, close the aperture G, and open the stop-cock, and the
pressure of the gas in the metre will be indicated by the rise of the
water on the scale board E, above its original height.


_Gas Mains, and Branch Pipes._

The name of _mains_, is given in the strictest sense of the word, to the
cast-iron pipes from two inches in diameter and upwards, placed under
ground, for conveying the gas into smaller branch pipes; but in a more
extended sense, the term is applied to every pipe from which smaller
ramifications or branch pipes proceed.

All mains destined to convey coal gas should be proved, they should be
submitted to the trial of sustaining a column of water 300 feet high,
and the pipe should be rejected if the least moisture appears on any
part of the side of the pipe whilst submitted to this trial. For
although such a pipe may remain impervious to gas for some time, the
imperfection or fissure which permits the water to issue through under
such a pressure, speedily increases, in consequence of the moisture to
which the main under ground must necessarily be exposed. A skilful
workman who is in the habit of proving pipes will distinguish, with an
astonishing degree of correctness, a faulty pipe, by the sound produced
by blows of the hammer upon the pipe. The faulty part, when struck upon,
produces a jarring sound very different from the clear sound which a
blow of the hammer produces when the pipe is in a perfect state. By this
means the workman also detects, by the ear, inequalities in the
thickness of the metal of the pipe.

Fig. 14, plate V., represents a longitudinal section of two flanch
pipes, and the mode of connecting them. _a_, and _b_, are the pipes with
their flanches connected; they are joined together, and rendered
air-tight, by first interposing between the flanches a coat of iron
cement, and then screwing up the faces of the flanches by means of screw
bolts and nuts.

The composition of the cement is as follows:

Take four ounces of flour of sulphur, and two of muriate of ammonia, and
mix them intimately together. When the cement is wanted, take five
ounces of the above mixture, and add to it six pounds of cast iron
borings, and blend them intimately together in a mortar; wet the mixture
with water, and when brought to a proper consistence, apply it to the
joints with a wooden or blunt iron spatula.

A degree of action takes place among the ingredients and the iron
surfaces to which it is applied, which at last causes the whole to unite
into one mass. In fact, after a time, the mixture and the surfaces of
the flanches become a species of pyrites (containing a very large
proportion of iron) all the parts of which cohere strongly together, and
form one mass. It is essential that no larger quantity of the
ingredients of the cement should be mixed up with water, than is
required for immediate use.

Fig. 15, plate V., represents a longitudinal section of a spigot and
faucet pipe. These pipes are most commonly used as gas mains. _a_, is
called the spigot, _b_, the faucet. The cavity between the inside of
one, and the outside of the other, is partly filled with rope yarn, or
oakum, and a good fitting of the two pipes being thus effected, melted
lead is poured into the cavity, which when set, is hammered in by the
end of a punch.

The inner parts of the faucet of these pipes ought to be no larger in
diameter than just to fit the spigot. This supports the pipe,
independently of the interposed lead and rope yarn, and prevents the
risk of hurting the joint from any external stress. The inner faucet is
commonly made about two and a half inches deep, and has the spigot
inserted one and a half inch into it. The practice of some manufacturers
is to make the outer faucet, or that which contains the lead six inches
deep, for all pipes above six inches in diameter; and to make the
faucets of all pipes below six inches, the same depth as the diameter of
the pipes. It is usual to make the space for the oakum and lead all
round the spigot, from one inch to one and a quarter inch; that width is
required, in order that the lead may be firmly driven into the joint.
When the space is very narrow, this cannot be done. On the other hand,
when too wide, there is a waste of lead, and a risk of injury from the
unequal expansion of the two metals.

All gas mains laid in public streets should be placed at least eighteen
inches below the surface of the ground, to secure them from being
disturbed by carriages, or interfering with the paving of the street;
they should be placed perfectly firm, so that they may not easily give

The course of all gas mains should be rectilinear, with a dip of about
one inch, in every ten feet distance.

In all wide streets, where the number of houses on both sides of the
streets, to be supplied with gas, is numerous, it is more economical to
employ a separate gas main for each side of the street, than to make use
of one larger main for both sides; because smaller mains may then be
employed, and the collateral branch pipes leading into the houses are
shorter; these circumstances amply compensate for the additional main.
All _branch_ pipes proceeding from a main, should have a dip of about
one inch in ten feet, towards the main from which they proceed, so that
any fluid that may happen to collect in these pipes must run into the

All small wrought iron branch pipes proceeding from the mains into the
houses or places to be lighted with gas, should be covered with a thick
coat of coal tar, before they are laid down into the ground; this may
easily be done by heating the pipe, and laying on the boiled tar with a

Every separate length of branch pipe should be tried by condensing the
pipe under water, in order to be certain that the pipe is sound. The
junctures of these pipes should be made by dipping the male screw of the
pipe into a mixture of white lead and linseed oil, before they are
screwed together.

Notwithstanding the usual care which can be taken in proving pipes,
before the gas is admitted into them, a slight leakage may be sometimes
subsequently detected.

Therefore, before the gas is suffered to enter the mains, they should be
again proved, in order to be certain that all the junctures are air
tight. The most convenient manner of proving the mains when laid, is by
means of a small portable gas holder filled with common air, and
connected by means of a small pipe, with the system of the mains to be
tried. This gas holder should be made to act with a pressure at least
four times greater than the pressure which the pipes will have to
sustain by the gas they are to convey. If the mains are air tight, the
gas holder will remain stationary, but if they are not sound, the gas
holder will descend, in proportion to the leak of the mains, the
quantity of gas lost may be thus ascertained.

Every quarter of a mile of pipe should thus be tried separately. In this
manner we become also enabled to detect instantly, whether any
collateral branch pipe has been left open by the workmen, a neglect by
no means uncommon in this department of the gas light business.

In order to guard against the danger of water entering from the external
surface into the pipes, a reservoir should always be placed at the
lowest point, where two or more descending mains meet and form an angle,
so as to receive the water that may happen to collect at this angular
point, an accumulation of which would cut off the communication between
the two pipes; this reservoir is usually called a siphon, see page 221.
It ought to be at least twice the diameter of the bore of the mains,
between which it is interposed, and four times that diameter in depth.
These reservoirs afford the best indication to show the sound or leaky
state of the system of the mains. In all instances where the pipes are
perfectly sound, observation has shown, that half a mile of gas mains,
three inches in the bore, does not deposit more than a quart of water in
a year; on the other hand, if the mains are leaky, the water of the
reservoir requires to be pumped out, sometimes as frequently as every
fortnight, and during wet weather, much oftener. The loss of gas by such
leakage is much greater than is generally imagined. Instances might be
mentioned where, in order to keep the common air out of a system of
faulty pipes, a constant influx of gas which a pipe two inches in
diameter can supply has been found necessary, and this of course is just
so much gas lost to the economy of the establishment.

With regard to the diameter of the mains, no general rule can be given.
It must vary according to the number of branch pipes and lamps which the
main has to supply within a given distance,--the angular direction of
the mains,--the pressure of the gas holder, and above all, with the
relative altitude of the place where the gas holder is situated, and the
place at which the gas is to be supplied, or where the lamps are placed.
Indeed this is one of the most important considerations with regard to
the economical distribution of gas mains, and by attending to this
circumstance, a prodigious saving may be effected.

If the gas flows through a main placed at an altitude of the gas holder,
and with a pressure to support a column of water half an inch high, this
gas at an altitude of 100 feet, will support a column of water ¹¹⁄₁₀
inch high, and as the velocity of the gas is as the ²√ of the height, or
pressure, the quantity of gas which will flow through a given opening at
an elevation of 100 feet, will be very nearly in the proportion of two
to three. Hence if a gas burner, or gas lamp, produces a flame two
inches high, at a place situated on a level with the base of the gas
holder, the lamp, if supplied by the same main, but situated 100 feet
higher, will burn with a flame three inches high.

This important fact may be rendered obvious in the following simple

Take a tube ten or fifteen feet long, and one inch in diameter, place it
horizontally; let one end of the tube be open, and close the other with
a plate pierced with a hole, of about ¹⁄₃₂ of an inch in diameter, and
then fill the tube with gas. If a lighted taper be applied to the hole,
when the tube is lying horizontally, the gas will not take fire; but on
raising the end of the tube where the small aperture is, the gas will
take fire, and the magnitude of the flame will become enlarged in
proportion as the tube approaches towards the perpendicular.

Hence the diameter of gas mains must be varied, according to the
altitude of the place to be supplied with gas. And it is in consequence
of neglecting this principle that we observe so frequently certain parts
of large towns scantily supplied with gas, whilst other parts furnished
from the same mains, situated considerably above the level of the gas
holder, have the gas in the greatest profusion, but at the expense of
those places situated at a lower level. And so true is this, that if a
main were to descend 100 feet below the base of the gas holder, and if
the pressure of the gas in the main was only equal to sustain a column
of water half an inch in height, the gas lamps could not be lighted at
all, at a point so low, because the pressure of the gas is then in an
equilibrium with the pressure of the atmosphere. Hence in lighting a
town or district with coal gas, the best situation for the gas
apparatus, as far at least as it regards the economy of the mains for
distributing the gas, is the lowest part of the town or district. For if
the mains are placed at an elevated situation, they require to be
proportionally larger, and if situated at a lower place than the level
of the gas holder, they must be smaller; but in either case the mains
must bear a proper proportion to each other, according to the conditions
and circumstances already stated, and it is here, where the skill of the
gas light engineer becomes conspicuous, for the saving that may thus be
effected in the lighting of a district or town with gas, is very

The requisite pressure of the gas for different situations with regard
to the altitude of the place to be lighted, may be readily known by
ascertaining the altitude of the place by means of the mountain
barometer. The Englefield mountain barometer is most commodious and
suitable for that purpose. This instrument is not liable to be out of
order, it may be used by a single observer, and affords an easy method
of ascertaining the elevations and depressions of the surfaces of the
earth with the greatest facility, and to a degree of precision, that may
vie with trigonometrical mensuration. Thus supposing the pressure of the
gas at the level of the gas holder to be equal to a column of water half
an inch high, by inspecting the height of the barometer, the requisite
pressure of the gas at that place may readily be found.

That part of a gas main which does not supply any gas to a branch pipe
or lamps, as it proceeds in its course need only be a quarter of the
capacity which is necessary at the part where the branch pipe or pipes
commence. For no inconvenience can arise from the increased velocity
which the gas must assume in proportion to the diminution of the bore
of the main, provided that the velocity of the gas is lessened by
passing into a main of a greater bore, prior to it being conveyed into
the pipe or pipes immediately connected with or supplying the lamps. The
enlargement of the pipes should be in the proportion to the diameter of
the two pipes, as four to one.

_Weight of cast iron Gas Mains of different lengths and bores._

In order to avoid that the gas mains deposited under ground in public
streets or other places, may not be on the one hand superfluously heavy,
or as it is called _thick in the metal_, and consequently unnecessarily
expensive, and on the other hand not too light, or too thin in the
metal, so as to be liable to become injured, we shall exhibit the weight
of gas mains of different bores and lengths best suited for conveying
gas, now employed at the best regulated gas works in the

  [50] A mile of pipe of an average diameter, laid under ground ready
  for conveying gas, together with taking up and making good the
  pavement, costs in London, about £. 1000.--And in small towns where
  the lights are usually less clustered together than is the case in
  London, and where pipes of three inches in the bore are usually
  sufficient, a mile of pipe complete costs about £. 700.

     _Bore of          _Length      _Weight
  cast iron pipes._   of pipe._     of pipe._
          INCHES.       FEET.       POUNDS.
            2             6            46
            2½            6            63
            3             9           120
            4             9           175
            5             9           248
            6             9           280
            7             9           364


_Gas Lamps, and Burners._

The lamps or burners for the combustion of coal gas, may be infinitely
and tastefully varied. The varieties commonly employed, are the Argand
burner, the Cockspur burner, and the Bat’s Wing burner.

The _Argand burner_, fig. 10, and 11, plate V., consists of two
concentric brass tubes, about one and a half inch long, and
seven-eighths of an inch in diameter, (the largest size burner
employed.) The interval between the two tubes is closed at top and
bottom. The upper part is closed with a ring of steel, it is perforated
with fifteen or eighteen holes ¹⁄₃₀ of an inch in diameter. The gas
enters into the cavity between the two tubes, and issues from the
circular row of apertures in the steel ring at the top of the burner
where it is burnt. A double supply of air within and without the flame
is effected by means of the glass which surrounds the flame. The
combustion of the gas is perfect when the admission of air is in due
proportion to the magnitude of the flame. The height of the gas flame
should never exceed three times the diameter of the flame. When the
flame is too large, the light is less brilliant, and it then produces an
odour, because the combustion is imperfect.

The best shape of the glass for surrounding the gas flame of the Argand
lamp, is a straight tube, shown fig. 8, plate V., or a tube enlarged at
the base, shown fig. 9, plate V. Fig. 10, plate V., is called a crutched
argand gas burner, it is used for pillar lamps; fig. 11, is called a
branch argand burner.

It is essential that the apertures for the emission of the gas of the
argand gas lamp, be perfectly round and of an uniform size, without this
condition the flame of the lamp is ragged, and not well defined.

Fig. 15, plate III., exhibits a swing bracket, furnished with a
_cockspur burner_. The burner consists of a hollow flattened globe,
about half an inch in diameter, pierced laterally with three or more
holes, of about ¹⁄₃₀ of an inch in diameter; out of these holes the gas
flame issues in streams as shown in the sketch. With this burner the
combustion of the gas is imperfect, and it is a wasteful mode of burning
coal gas. The surrounding holes of the cockspur burner, was it not for
the upward current of air, would give flames radiating in straight lines
from the centre of the burner, but the ascending current of heated air,
causes them to curve upwards like the spur of a game cock, and hence the
name cockspur burner.

If the gas be made to burn from a series of holes made in the lateral
circumference of a hollow flat cylinder, it will produce a circular
horizontal series of flames curving upwards.

Fig. 12. plate V., is called a _bat’s wing_ burner; it consists of a
small pear-shaped steel burner, about ¹⁄₁₆ of an inch in diameter,
having a perpendicular slit at its upper extremity, about ¹⁄₄₀ of an
inch in diameter. This burner exhibits a tulip-shaped flame, as shown
fig. 13, plate V., it is well adapted for street gas lamps.

The stop-cock for admitting gas into gas burners should always be placed
at least six inches from the burner. The stop-cock in the brackets, fig.
8, or 9, plate V., is placed at _a_. _Pendant gas lamps_, into which the
gas is conveyed from a pipe above, through the ceiling, should be
provided with a mercurial joint, or ball and socket joint. The former
contrivance is preferable, because it can never leak;[51] but the latter
requires occasional repairs. Fig. 14, plate III., shews the mercurial
joint. _a_, is the pipe which brings the gas; it terminates in a sheet
iron cup open at bottom, but closed air tight at the top; this cup is
inverted into a small iron bason, containing mercury. D the iron tube
which communicates with the gas lamp or burner, and the upper extremity
of which projects above the surface of the mercury in the iron bason,
whilst the other extremity proceeds to the burners or lamps.

  [51] This contrivance has been adopted throughout the fitting up of
  the gas lights at the Royal Mint.

_Swing bracket burners_, fig. 13, plate III., should have the axis of
motion at the joints A, A, A, perforated at right angles to each other,
so as to admit the moveable joints at A, to be left open, without
obstructing the passage of the gas when the bracket assumes different
angular positions. All swing brackets ought to have a double, and not a
single joint, because the latter soon wears oval in the two opposite
edges; this is prevented by the double joint having an uniform bearing
at top and bottom, it therefore can never leak.

Fig. 11, plate VI., exhibits the arrangement usually adopted for a
_pendant perpendicular sliding lamp, or chandelier_, which requires to
be raised or depressed. This contrivance is convenient for lighting
theatres, or public buildings, by means of a large central gas light
chandelier, that may be raised or depressed at pleasure.

The gas enters into the tube _D_, which is firmly fixed in the ceiling,
as shown in the sketch; it passes through a hole near E, into a smaller
tube _j_, which slides perpendicularly within the tube D. This sliding
tube is made air tight by means of two stuffing boxes filled with oil,
placed near B, and C. The sliding tube _j_, together with the chandelier
suspended to it, is counter-balanced by a weight concealed in a box W,
connected with pullies in the usual manner, as shown in the sketch, so
that the chandelier may be raised or lowered at pleasure.

_Directions to Workmen, for adapting Gas Pipes to the interior of

The adapting gas pipes to the interior of houses, for the supply of gas,
simple and easy as it may appear, has been the means of not a little
contributing to bring the gas light illumination, on many occasions,
into disrepute. It has required years to enable workmen of the best
intention to acquire sufficient practical skill in the proper execution
of a business, which must be pronounced to constitute an art entirely
new, and in which no progress could be made, but after having committed
many errors. A house neatly and judiciously fitted up with gas pipes,
displays to a person experienced in this art, a skill and judgment,
equal to what is established in any other branch of mechanical
employment. It must be obvious, that the art of arranging the pipes and
adapting them, is one of that class of operations in which it is a real
saving to employ the best materials and skilful workmen, to avoid
repairs and subsequent alterations and derangements of the work. The
supply and distribution of the pipes, or the _fitting up_, as it is
called by the workmen, may be done almost at any price with regard to
workmanship and materials, and to bargain for cheapness in the execution
of it, with a faithful, honest, and skilful workman, must naturally be a
losing concern to the person for whom the work is done. The cost of
furnishing and adapting the pipes to one place, cannot serve as a
standard for any other place, every separate place may present
difficulties which could not be foreseen at the commencement of the

The stopping up and corrosion of the gas pipes, which at the
commencement of the introduction of the new lights was complained of in
many places, it is now sufficiently established, originated entirely
from the impurity of the gas, together with a faulty arrangement of the
pipes, in consequence of which, the water of condensation accumulating
in certain parts, exercised a strong chemical action on the copper
pipes, and if the gas was not very pure, ultimately corroded the pipe.
These objections do no longer exist, and it may safely be pronounced,
that pure coal gas produces no action whatever on the copper tubes
through which it is conveyed. In proof of this statement, we need only
refer to the several districts of the metropolis, fitted up with gas
pipes at the first introduction of the new lights, (1809,) all of which
are still in perfect preservation.

It is perhaps unnecessary to add, that no pipe capable of being melted
by a gas flame, should ever be employed for conveying or distributing
gas through the interior of houses, because the facility with which such
pipes might be perforated, could lead to serious consequences, if the
gas issuing from the aperture of the pipe were lighted, the flame in
that case would follow the melted part, through the whole extent of the
pipe, and the hazard by fire would be considerably increased.
Therefore, pewter, lead, and tin pipes, are very improper for
distributing gas through the interior of houses, and should never be
used for that purpose. Hence copper, and iron pipes, are universally

In order that the pipes for conveying the gas from the mains, and
distributing it through the houses or other buildings to be lighted with
gas, may in the first place not be unnecessarily large, or too small,
the following rule may serve as a guide to workmen:

One gas lamp,--consuming four cubic feet of gas in an hour, if situated
twenty feet distance from the main which supplies the gas, requires a
tube not less than a quarter of an inch in the bore.

Two lamps,--30 feet distance from the main, require a tube ³⁄₈ of an
inch in the bore.

Three lamps,--30 feet distance from the main, require a tube ³⁄₈ of an
inch in the bore.

Four lamps,--40 feet distance from the main, require a tube ¹⁄₂ inch in
the bore.

Six lamps,--50 feet distance from the main, require a tube ⁵⁄₈ of an
inch in the bore.

Ten lamps,--100 feet distance from the main, require a tube ³⁄₄ of an
inch in the bore.

Fifteen lamps,--130 feet distance from the main, require a tube 1 inch
in the bore.

Twenty lamps,--150 feet distance from the main, require a tube 1¹⁄₄ inch
in the bore.

Twenty-five lamps,--180 feet distance from the main, require a tube 1⁵⁄₈
of an inch in the bore.

Thirty lamps,--200 feet distance from the main, require a tube 1¹⁄₂ inch
in the bore.

Thirty-five lamps,--250 feet distance from the main, require a tube 1⁵⁄₈
of an inch in the bore.

All copper pipes employed to convey gas through the interior of houses
should be of the following weight, with regard to a given length of the

  _Bore of the pipe._    _Weight per foot._
   PARTS OF AN INCH.           OUNCES.
        ²⁄₈                       3
        ³⁄₈                       5
        ¹⁄₂                       6
        ⁵⁄₈                       8
        ³⁄₄                      10

No coppered pipes should be used but such as have wrapt over and brazed
joints. They should be well annealed, to render them pliable without
being liable to break.

All the bends for connecting pipes must be circular, see fig. 22, plate

No branch pipe ought to proceed from a pipe of a quarter of an inch in
the bore, and no more than two branch pipes should proceed from a pipe
three-eighths of an inch in the bore.

All branch pipes before they are fixed for conveying gas, must be proved
by condensing air into them by means of a condensing hand pump. The pipe
should be placed in a trough of water, the leak will then be easily
observed by the air bubbles which rise through the water whilst the air
is condensed in the pipes.

All branch pipes should have a rectilinear course; pipes that are
twisted have an unsightly appearance.

All pipes should have a descent of no less than a quarter of an inch in
four feet.

The seams or brazed part of the pipes must always be out most and not
towards the wall; because if a leak should happen to take place in the
brazed part of the pipe, it may then be easily discovered and more
readily repaired.

When all the pipes have been furnished to a house or place intended to
be lighted, the whole system of the pipes should be examined with the
utmost rigour, to ascertain whether all the junctures are air tight.
This should be done by condensing air into the pipes by means of a
condensing syringe, and if the piston of the syringe lowers after
condensation, it is a sure indication that the pipes are faulty, and
consequently totally unfit for receiving the gas. The leak may be
detected by passing a lighted taper carefully along the whole extent of
the pipe filled with condensed air, when the flame of the taper will be
affected as it passes over the faulty place of the pipe.

The aperture from which the gas can escape may however, be so small, as
to render it a matter of difficulty to discover it in the manner just
stated; but when the pipes are filled with coal gas, the escape of it,
when all the stop-cocks of the lamps and burners are shut, will soon
become obvious, by the peculiar odour of the gas, if the apartment, or
place, where the pipes are placed, is suffered to be closed for about
twenty-four hours. The gas should not be introduced into pipes in which
any defect of this kind is found, until it be completely removed. The
most severe trial to ascertain the air tightness of any system of pipes
is, the trial by exhaustion, by means of an air pump, for the guage of
the pump will discover the minutest leak, which the preceding method of
proving pipes can not discover.

All pipes after being proved should be painted of the same colour as the
surface to which they are affixed.

The whole system of pipes should incline to one or more places, so that
any moisture that may happen to accumulate in the pipes, may collect at
such places, whence it may be readily removed by opening a screw plug
adapted for that purpose.

All the different junctures of mains and branch pipes, should be
effected by means of connecting pieces, so that any part of the system
of the pipes, or any separate branch pipe may readily be detached, and
put up again if occasion should require it; fig. 19, plate V., exhibits
this mode of connecting gas pipes by means of union joints. A, B, C, D,
E, shows a gas pipe with its union or connecting joint, divided into its
separate parts. _D_, is a collar of leather, which passes over the part
C, of the union joint, close up to the shoulder of the joint; the
opposite extremity of the pipe may be inserted into the socket _B_, so
that the shoulder C, comes in contact with the fillet or rim in B, to
prevent it passing over the shoulder C, when B and E are screwed
together. The latter part of the pipe is furnished with a male screw to
correspond with the thread in the collar B. The shoulder piece C, is of
rather a larger diameter than the bore of the tube A, with which it is
to be connected. The short piece E, furnished with a male screw, is of
the same diameter as the part C. The pieces C, and E, of the pipe are
soft soldered, one to the tube A, and the other to the tube E, but
previous to soldering on C, it is necessary that the socket should be
inserted into the tube A, it will then be ready for connecting, as will
become obvious by inspecting fig. 20, which shows the various parts of
the union joint fitted for use. It is evident that if the extremity D,
in the pipe B, be brought close to the pipe E, and if the socket C, be
moved along the pipe A, and screwed upon the male screw at D, as far as
it will go, the face of the part D, must press close against the leather
collar which is placed on E, and render the joint gas tight. These kind
of joints are very convenient for circular bends, fig. 22, and T,
pieces, fig. 21. The T pieces, fig. 21, are very useful for collateral
branch pipes, either for the same or of a less diameter as the pipe,
from which they proceed, so as to branch off at right angles.

Fig. 22, is a quarter circular bend; it is convenient for adapting tubes
along the angular parts of rooms, and to all such situations where the
tube is to have a sudden circular course. Small copper tubes may be
readily bent to the required angle without breaking, but if a tube
should terminate in any angular part of a room, in that case a circular
bend furnished with a male and female screw, is convenient for
connecting the pipes together.

All pipes adapted to the exterior of buildings, should be kept a little
distance off from the wall, to prevent the wet lodging between the pipe
and the surface to which they adapted.

Sheet iron mains for the interior of houses, are preferable to copper
mains, provided the course of the main with regard to the position of
the branch pipes, does not require too many angular directions, or
circular bends.


_Illuminating power of Coal Gas, and quantity of Gas consumed in a given
time, by different kinds of Burners, and Gas Lamps._

The illuminating power of coal gas, differs according to the nature of
the coal from which it is obtained, and the manner in which it is
purified, together with the quantity of naptha or essential oil
chemically combined, or mechanically suspended in the gas. For if the
gas be strongly agitated with water, its illuminating power is
diminished. Coal gas, which abounds in olifiant gas or supercarburetted
hydrogen possesses the greatest illuminating power, and hence
carburetted hydrogen obtained from the decomposition of coal tar
possesses a greater illuminating power than the gas obtained from the
coals which produced the tar. The illuminating power of carburetted
hydrogen obtained from coal tar when compared to the gas obtained from
the best Newcastle coal is in the proportion as six to five. In fact the
intensity of light evolved during the combustion of gazeous bodies
composed of carbon, hydrogen, and oxigen, is always in the ratio of the
quantity of carbon contained in equal quantities of the gazeous
compound, and hence the gas from animal oil which is chiefly composed of
supercarburetted hydrogen or olifiant gas, surpasses in illuminating
power the gas obtained from coal.

Half a cubic foot of coal gas, obtained in the ordinary way of
manufacturing coal gas, from Newcastle coal, is equal in illuminating
power and duration of time, to the light produced by a tallow candle six
in the pound, burning for one hour, and as such a tallow candle lasts
five hours, therefore fifteen cubic feet of coal gas, are equal in value
with regard to illuminating power to one pound of candles. And as 112
pounds of Newcastle coal produce by the new method of manufacturing coal
gas, at least 550 cubic feet of gas, therefore the quantity of gas
produced from a chaldron of Newcastle or Sunderland coal, (the minimum
weight of which is 27 cwt.) is equal in illuminating power to 1000
pounds of tallow candles.

The illuminating power of coal gas may readily be ascertained. Though
the eye is not fitted to judge of the proportional power of different
lights, it can distinguish in many cases with sufficient precision where
two similar surfaces are equally illuminated. As the lucid particles
emitted from luminous bodies are darted in right lines, they must spread
uniformly, and hence their density diminishes in the duplicate ratio of
their distance. From the respective situations, therefore, of the
centres of divergency, when the contrasted and illuminated surfaces
become equally bright, we are enabled to compute their relative degrees
of intensity. And for this purpose it is assumed as a principle, that
the same quantity of light, diverging in all directions from a luminous
body, remains undiminished in all distances from the centre of

Thus we must suppose, that the quantity of light falling on every
object, is the same as would have fallen on the places occupied by the
shadow; and if there were any doubt of the truth of the supposition, it
might be confirmed by some simple experiment.

Therefore, it follows, that, since the shadow of a square inch of any
surface occupies at twice the distance of the surface from the luminous
point the space of four square inches, the intensity of the light
diminishes as the square of the distance increases. If, consequently, we
remove the two sources of light to such distances from an object that
they may illuminate it in equal degrees, we are authorized to conclude
that their original intensities are inversely as the squares of the

Hence, if two lights of unequal illuminating powers shine upon the same
surface at equal obliquities, and an opaque body be interposed between
them and the illuminated surface, the two shadows produced must differ
in blackness or intensity in the same degree. For the shadow formed by
intercepting the greater light, will be illuminated by the smaller light
only; and reversely, the other shadow will be illuminated by the greater
light; that is to say, the stronger light will be attended with the
deeper shadow.

Now it is easy by removing the stronger light to a greater distance, to
make the shadow which it produces equal to that afforded by the less
light. Experiments of this kind may be made in the following manner:

Fasten a sheet of white paper against the wall of a room, and place the
two lights intended to be compared, so that the rays of light from each
fall with nearly the same angle of incidence upon the middle of the
paper. In this situation, if a book or other object be held to intercept
part of the light, which would have fallen on the paper, the shadows may
be made to appear as in this figure:


where A represents the surface illuminated by one of the lights
only; B, the surface illuminated by the other light; C, the perfect
shadow from which both lights are excluded. It will easily be understood
that the lights about D and E, near the angle F, will fall with equal
incidences when the double shadow is made to occupy the middle of the
paper; and consequently, if one or both of the lights be removed
directly towards or from the paper, as the appearances may require,
until the two shadows at E and D have the same intensity, the quantities
of light emitted by each, will be as the squares of the distances from
the paper.

By experiments of this kind, many useful particulars may be shewn; for,
since the cost and duration of candles, and the consumption of coal gas,
or oil in lamps, are easily ascertainable, it may be shewn whether more
or less light is obtained at the same expense during a given time, by
burning a number of small lights, instead of one or more of greater
intensities. And thus we may compare the power of different kinds of
lamps or candles, with gas lights of different intensities, so as to
determine the relative cost of each particular kind of the combustible
substance employed for furnishing light. For example; if a candle and a
gas burner supplying coal gas, adjusted by a stop-cock, produce the same
darkness of shadow, at the same distance from the wall, the strength or
intensity of light is the same.

An uniform degree of intensity of the gas light may readily be
produced, by opening or shutting the stop-cock, if more or less light be
required, and the candle kept carefully snuffed to produce the most
regular and greatest quantity of light. The size of the flame, in
experiments of this kind, of course becomes unnecessary, and will vary
very much with the quality or chemical constitution of the coal gas. The
bulk of the gas consumed, and the weight of tallow or oil used by
weighing the candle or oil before and after the experiment furnish the
data for calculating the relative cost of tallow, or oil and gas, when
compared with each other.

The following statement exhibits the quantity of coal gas consumed in a
given time, by different kinds of argand lamps. An argand burner which
measures in the upper rim half an inch in diameter, between the holes
from which the gas issues, when furnished with five apertures ¹⁄₂5 part
of an inch in diameter, consumes two cubic feet of gas in an hour, when
the gas flame is one and a half inch high. The illuminating power
produced by this burner is equal to three tallow candles eight in the

An argand burner three quarters of an inch in diameter between the
holes in the upper rim, and perforated with holes, ¹⁄₃₀ of an inch in
diameter, consumes three cubic feet of gas in an hour, when the flame is
two and a quarter inches high, and produces a light equal in intensity
to four tallow candles, eight in a pound.

An argand burner seven-eighths of an inch in diameter, perforated with
eighteen holes ¹⁄₃₂ of an inch in diameter, consumes when the flame of
the gas is three inches high, four cubic feet of gas in an hour, and
produces a light equal in intensity to six tallow candles, eight in the

When the flame obtained by these kind of burners rises to a greater
height, than what has been stated, the combustion of the gas is
imperfect, the intensity of the light becomes diminished, and there is a
waste of gas. The same holds good with regard to the size of the holes
from which the gas issues; if the holes be made larger than ¹⁄₂5 part of
an inch in these kind of burners, the gas is not completely burnt, and
its illuminating power decreases.

The height of the glass which surrounds the flame, should never be less
than five inches, and the interval for the current of air within and
without the flame, ought to bear the usual proportion adopted for the
combustion of oil in the common argand lamps of similar diameters.

_Ventilation of Apartments lighted by Coal Gas._

Before means had been devised for the effectual purification of coal
gas, a disagreeable odour was found to attend its combustion in an
impure state, and hence an opinion became prevalent, that the benefit of
this new species of illumination must be confined to open places, and
that it could not with any regard to pleasure or salubrity, be adapted
to private dwellings.

The art of purifying coal gas, has at length however, been carried to
such a perfection, that every possibility of a disagreeable odour
arising from its combustion has been wholly removed, in all cases where
attention is paid to the perfect combustion of the gas, by keeping the
flame of the same of a proper magnitude.

And since this improvement, the use of coal gas, as a means of
illumination has become as general, and has been found attended with as
superior advantages within doors as without, and hence a vast number of
dwelling houses are now lighted throughout with gas.

Although there is no occasion therefore, to make provision for
ventilating apartments where gas light is employed, on account of any
odour which it can produce when honestly used, so that the combustion is
perfect, yet on other accounts such means of ventilations are very
salutary and necessary.

The flame of coal gas produces a degree of heat,[52] which in some
places, such as large public offices, and warehouses of dry goods, is a
strong additional recommendation in favour of its use, (page 15,) while
in others, on the contrary, such as small rooms numerously frequented,
and shops containing commodities requiring to be kept cool, it can only
be used beneficially when means are provided for conveying away the
heated air.

  [52] Mr. Dalton’s method of ascertaining the comparative effect of
  heat evolved during the combustion of inflammable gases, and other
  substances capable of burning with flame, (Dalton’s System of
  Chemistry, vol. I. p. 76,) is simple, easy, and accurate. It is as

  Take a bladder of any size, (let us suppose for the sake of
  illustration, the bladder to hold 30,000 grains of water,) and having
  furnished it with a stop-cock and small jet pipe, fill it with the
  combustible gas the heating power of which is to be tried. Take also a
  tinned iron vessel with a concave bottom of the same capacity, pour
  into it as much water as will make the vessel and water together equal
  to the bulk of the water in the bladder, viz. 30,000 grains. Then set
  fire to the gas at the orifice of the pipe, bring the point of the
  flame under the bottom of the tinned vessel, and suffer it to burn
  there, by squeezing the bladder till the whole of the gas is consumed.
  The increase of temperature of the water in the tinned vessel before
  and after the experiment, expresses very accurately the heating power
  of the given bulk of the inflammable gas. It was thus proved that--

  Olifiant gas raises an equal volume of water 14 deg.
  Carburetted hydrogen, or coal gas            10
  Carbonic oxid gas                             4
  Hydrogen gas                                  5
  Spermaceti oil, 10 grains burnt in a lamp
    raised 30,000 grains of water               5
  Tallow                                        5
  Wax                                           5,75
  Oil of turpentine                             3
  Spirit of wine                                2

The best method for this purpose is to make an aperture of about two or
three inches in diameter into the chimney near the ceiling, and
inserting into it a tube bending upwards into the interior of the
chimney. A complete ventilation of the room will thus be established, by
producing an extra vent which will be amply sufficient for carrying off
the heated air. The aperture can easily be masked with some ornamental
open work, corresponding with the style of the room.

If there happens to be no chimney in the apartment, the ventilator may
be made in the ceiling, and the tube may be carried between the ceiling
and the floor above, into the open air. The mode of ventilation now
suggested, has been uniformly found most efficient, and has, under
existing circumstances, a decided superiority over another method, which
we see in some instances adopted. This method consists in enclosing the
gas burner in a bell-shaped glass, from the upper part of which a large
copper tube proceeds, and leads out into the open air. It is certain
that by this means not only the heated air is carried off, and the
possibility of any waste gas escaping into the apartment is also
completely prevented. But at the same time, by taking away all occasion
for a prudent limitation in the use of the gas, it exposes it to a
degree of improvident waste, in the hands of dishonest and careless
individuals, which must prove ruinous to the manufacturer. The mode of
regulating the light of the flames by means of the governor, of which a
description has been given, page 232, indeed provides a check against
such waste, and there can be no doubt that in proportion as this
instrument gets into general use, the objection on this score must of
course fall to the ground; but under any circumstances the inelegance of
the contrivance of such an object in a chamber, as the large branching
tube, must always induce a preference, for the more simple, and for all
necessary purposes, equally efficient method, of the ventilator before


_Gas from Coal Tar._

Although the tar which forms one of the products obtained from the
decomposition of pit coal, in the manufacture of coal gas, has become an
article of commerce, being found applicable to most of those purposes to
which vegetable tar has hitherto been used, it appears from experiments
made on a large scale, that instead of thus disposing of the coal tar,
it is more profitable, under certain circumstances, to submit this
substance to a destructive distillation, for the purpose of obtaining
from it carburetted hydrogen gas, which it is capable of affording, not
only in abundance, but of a superior quality.

The chief circumstances which must determine the manufacturer of coal
gas in this respect, is the price at which he can sell the coke produced
in his establishment. If the price of this article is high, if he finds
a ready market for coke, there is every reason to believe, that the
manufacturer will find it more to his advantage to dispose of the tar,
and to manufacture gas from coal alone, in order to increase his store
of coke. But if coke happens to be at a low price, and not disposable
with advantage, the manufacturer will do well to make the coal go as far
as possible in the production of gas, and under such circumstances he
will keep and convert the tar into gas, thus consuming less coal and
having less of the burdensome article, coke, to dispose of.

The profit however, to be gained from the sale of coke, must be both
certain and considerable, to induce a preference for the former course;
because the decomposition of coal tar, besides superseding a
proportionate quantity of coal, is attended with several other very
tempting advantages.

From experiments lately made in the metropolis on this subject, in which
I have been engaged, it appears that in all large gas light
establishments, where the quantity of coal tar rapidly accumulates, and
must be got rid of, and in all places where the tar cannot be sold for
more than four shillings the hundred weight, it will be certainly
advantageous to the manufacturer to decompose the tar for the production
of carburetted hydrogen gas.

The price of coal cannot effect the operation, because where coal bears
a high price, the manufacturer of the tar gas, will diminish the
quantity of coal which he would otherwise be called upon to employ for
the production of the requisite quantity of gas. And in places where
coal is cheap, the decomposition of the tar will be attended with less

The carburetted hydrogen gas produced from coal tar, possesses a greater
illuminating power than the gas obtained from coal.[53] It consists
chiefly of supercarburetted hydrogen or olifiant gas, and a less
quantity of it is of course sufficient.

  [53] Vegetable tar, also affords carburetted hydrogen gas in
  abundance, and this no doubt might be employed to great advantage for
  the production of artificial light in places where it is cheap. 212
  pounds of the most viscid Swedish tar, produce 1484 cubic feet of
  carburetted hydrogen, (or seven cubic feet to one pound of tar,) the
  illuminating power of this gas is equal to the gas obtained from pit

The gas thus obtained, is purified likewise with far greater facility,
taking only one hundred and twentieth part of the quantity of quicklime
which is required for the purification of carburetted hydrogen obtained
from pit coal. The apparatus for the production of carburetted hydrogen
from coal tar, is moreover less bulky, less expensive, and less
complicated; and it can be managed by fewer workmen. And as the combined
result of these several advantages, it is obvious, that by the
substitution of coal tar, the new mode of lighting by gas can be pursued
on a smaller scale; which it can never be with any profit, where coal
itself is immediately employed for the production of the gas.

The apparatus employed by Mr. Clegg, for the distillation of tar, is
extremely simple. It consists of two hollow cast iron cylinders, twelve
inches in diameter, and nine feet long, furnished with moveable lids or
mouth pieces, and joined together at the extremity opposite to the mouth
piece. These cylinders are fixed in a brick furnace, so that each
inclines eleven degrees, one above and the other below the horizontal
base of the furnace.

When the apparatus has acquired a dull red heat, the coal tar is
suffered to flow into the upper cylinder, by small portions at a time.

The tar is contained in a closed vessel, situated at any convenient
place above the apparatus. It has a small aperture for the admission of
air. But as a sufficient small quantity of viscid tar does not flow
freely in a thin stream, a larger portion than is wanted, is made to
flow first into a a small box, upon the apex of a pyramid which divides
the stream, so that the excess runs off by a waste pipe, whilst a due
quantity only is conveyed into the retort where it is decomposed.

This apparatus[54] therefore differs only from the apparatus described
in the Journal of Science and the Arts, 1816, No. II., p. 282; that the
cylinders may be detached, for cleaning them out more conveniently.

  [54] Now erecting at Birmingham.

The following statement exhibits the result of a series of experiments,
made (1816,) at the Westminster Chartered Gas Light Establishment,[55]
for the purpose of ascertaining how far, and under what circumstances
the decomposition of coal tar is a measure of economy.

  [55] Communicated by Mr. T. S. Peckston.

  Two tar retorts worked seven hours, produced 3054 cubic feet of gas.
  The quantity of tar decomposed, amounted to 354 lb. therefore 8 cubic
  feet of gas, (omitting fractions), were obtained from 1 lb. of tar.

  Two tar retorts, worked nine hours, produced 4591 cubic feet of gas.
  The quantity of tar decomposed, was 525 lb. Hence 1 lb. of tar yielded
  nearly 8³⁄₄ cubic feet of gas.

  Fifteen cwt. 16 lb. of tar, produced 16,112 cubic feet of gas, = 9¹⁄₂
  cubic feet of gas, to 1 lb. of tar.

  Five cwt. 3 quarters, 22 lb. of tar, produced 6660 cubic feet of gas,
  = 10 cubic feet of gas to 1 lb. of tar.

  Five cwt. 17 lb. of tar, produced 5193 cubic feet of gas, = 9 cubic
  feet of gas to 1 lb. of tar.

  One cwt. 81 lb. of tar, produced 1737 cubic feet of gas, = 9 cubic
  feet of gas to 1 lb. of tar.

  One cwt. 30 lb. of tar, produced 1313¹⁄₂ cubic feet of gas, = 8 cubic
  feet of gas to 1 lb. of tar.

  Five cwt. of tar, produced 5880 cubic feet of gas, = 10¹⁄₂ cubic feet
  of gas to 1 lb. of tar.

  Two cwt. of tar, produced 2072 cubic feet of gas, = 9¹⁄₂ cubic feet of
  gas to 1 lb. of tar.

  Three cwt. 18 lb. of tar, produced 3717 cubic feet of gas, = 10¹⁄₂
  cubic feet of gas to 1 lb. of tar.

  Two cwt. 6 lb. of tar, produced 2242¹⁄₂ cubic feet of gas, = 9³⁄₄
  cubic feet of gas to 1 lb. of tar.

From the preceding operations it becomes obvious, that 9¹⁄₂ cubic feet
of gas, were obtained in the large way from 1 lb. of tar. But this
proportion appears evidently too small, our own operations assign
fifteen cubic feet of gas to one pound of tar. Professor Brande,
obtained eighteen cubic feet[56] from the same quantity of tar.

  [56] Journal of Science and the Arts, 1816, No. II. p. 282.

_Gas from Oil._

“Messrs. J. and P. Taylor[57] are the first persons who have resorted to
oil as a substance from which gas for illumination could be easily and
cheaply prepared; and in the construction of a convenient apparatus for
the decomposition of this body, they have fully shewn its numerous
advantages over coal, while they have afforded the means of producing
the most pure and brilliant flame from the inferior and cheap oils,
which could not be used in lamps. The apparatus for the purpose is much
smaller, much simpler, and yet equally effectual, with the best coal gas
apparatus. The retort is a bent cast iron tube, which is heated red by a
small convenient furnace, and into which oil is allowed to drop by a
very ingenious apparatus; the oil is immediately volatilized, and the
vapour in traversing the tube becomes perfectly decomposed. A mixture of
inflammable gases, which contains a great proportion of olifiant gas
passes off; it is washed by being passed through a vessel of water
(which dissolves a little sebacic acid, and which seldom requires
changing), and is then conducted into the gasometer.”

  [57] Copied from the Journal of Science and the Arts, Vol. VI. p. 108.

“The facility and cleanliness with which gas is prepared from oil in the
above manner, may be conceived from the description of the process. A
small furnace is lighted, and a sufficient quantity of the commonest oil
is put into a small iron vessel, a cock is turned, and the gas after
passing through water in the washing vessel, goes into the gasometer.
The operation may be stopped by shutting off the oil, or, to a certain
extent, hastened by letting it on more freely; the small quantity of
charcoal deposited in the retort is drawn out by a small rake, and the
water of the washer is very rarely changed.”

“The gas prepared from oil is very superior in quality to that from
coal; it cannot possibly contain sulphuretted hydrogen, or any
extraneous substance; it gives a much brighter and denser flame; and it
is also more effectual, i. e. a lesser quantity will supply the burner
with fuel. These peculiarities are occasioned, in the first place, by
the absence of sulphur from oil, and then by the gas containing more
carbon in solution. As the proportion of light given out by the flame of
a gaseous compound of carbon and hydrogen, is in common circumstances in
proportion to the quantity of carbon present; it is evident that the gas
which contains a greater proportion of olifiant gas, or supercarburetted
hydrogen than coal gas, will yield a better and brighter light on

“It is necessary, in consequence of the abundance of charcoal in
solution, to supply the gas when burning with plenty of atmospheric air,
for as there is more combustible matter in a certain volume of it, than
in an equal volume of coal gas, it of necessity must have more oxigen
for its consumption.[58] The consequence is, that less gas must be burnt
in a flame of equal size, which will still possess superior brilliancy;
that less is necessary for the same purpose of illumination; and that
less heat will be occasioned. From five and a half to six cubical feet
of coal gas are required to supply an Argand burner for an hour; two
cubical feet to two and a half of that from oil, are abundantly
sufficient for the same purpose.”

  [58] Dr. W. Henry’s experiments gave the following result:--100 cubic
  inches of carburetted hydrogen from coal, require, for burning, 220
  cubic inches of oxigen, and produce 100 cubic inches of carbonic
  acid--100 cubic inches of carburetted hydrogen gas procured from lamp
  oil, require 190 cubic inches of oxigen, and produce 124 cubic inches
  of carbonic acid,--100 cubic inches of carburetted hydrogen obtained
  from wax, require 280 cubic inches of oxigen, and produce 137 cubic
  inches of carbonic acid.

“One important advantage gained by the circumstance, that so small a
quantity of this gas is necessary for burners is, that the gasometer
required may be small in proportion. The gasometer is the most bulky
part of a gas apparatus, and that least capable of concentration; and
where-ever it is placed, it occupies room to the exclusion of every
thing else. Some very ingenious attempts have been made to diminish its
size and weight, as in the double gasometer,[59] and others, but without
remarkable success. Here, however, where the room required to contain
the gas is directly diminished, the object is so far obtained; and when
that takes place to one half, or even one third, it is of very great
importance. It in a great number of cases brings the size of the
apparatus within what can be allowed in private houses; and in
consequence of the rapidity with which the retort can be worked, the
gasometer may again be reduced to a still smaller size.”

  [59] This contrivance is more expensive and complicated than any of
  the gas holders of which a description has been given; nor is it safe,
  for if the slightest leak should happen in the interior vessel of the
  double gas holder, an explosive mixture would be formed, and dreadful
  consequences might follow; this can never be the case with any of the
  machines now in use.--_Note of the Author._

“Another advantage gained by the small quantity of gas required for a
flame, is the proportionate diminution of heat arising from the lights.
The quantities of heat and light produced by the combustion of
inflammable gases are by no means in the same constant relation to each
other; one frequently increases, whilst the other diminishes; and this
is eminently the case when coal gas and oil gas are burned against each
other. The quantity of heat liberated is, speaking generally, as the
quantity of gas consumed, and this is greatest with the coal gas; but
the quantity of light is nearly as the quantity of carbon that is well
burnt in the flame, and this is greatest in the oil gas.”

“The very compact state in which the apparatus necessary for the
decomposition of oil can be placed, the slight degree of attention
required, its certainty of action, its cleanliness, and the numerous
applications which it admits of in the use of its furnace for other
convenient or economical purposes, render it not only unobjectionable,
but useful in manufactories and establishments; and these favourable
circumstances are accompanied, not from any inferiority in the flame or
increased expense, but by an improved state of the first, and saving in
the latter.”

“Messrs. Taylor have shewn great ingenuity in the construction of their
whole apparatus, but the washer and gasometer deserve particular notice
for their remarkable simplicity also. In the washer, two planes are
fixed in a box or cistern, in a direction not quite horizontal, but
inclined a little in opposite directions; the planes are traversed
nearly across by slips of wood or metal, fixed in an inclined position
on the under surface, and which alternately touch one side of the
cistern, leaving the other open and free. These planes being immersed in
water, the gas is thrown in under the lowest ridge, and by its ascending
power is made to traverse backward and forward along the ridges fixed
on the planes, until it escapes at the highest part of the uppermost
ridge. Thus, with a pressure of five or six inches of water only, it is
made to pass through a distance of fourteen or sixteen feet under the
surface of the fluid, and becomes well washed.”

“The smaller gasometers are made of thin plate iron, and being placed in
a frame of light iron work, look more like ornamental stoves than the
bulky appendages to a gas apparatus, which they supply. The larger ones
are made very light, and when in pieces very portable, by being
constructed of a frame of wood work, in the edges of which are deep
narrow grooves; plates of iron fit into these grooves, which being
caulked in and painted over, make a light and tight apparatus. These are
easily put together in any place, and may therefore be introduced into a
small apartment, or other confined space, where a gasometer already made
up would not enter.”

For the following additional information on this subject, I am indebted
to Messrs. J. and P. Taylor.

“The economy of obtaining gas for the production of light from oil, may
be judged of from the following data.”

“One gallon of common whale oil, produces about ninety cubic feet of
gas.[60] An argand burner required a cubic foot and a half of gas per
hour; and consequently a gallon of oil when converted into gas, will
supply the same burner for sixty hours. The expence of the gas at a
moderate price of oil, will be, allowing for coals, labour, &c. for
producing the gas, three farthings per hour, and such a burner will give
a light, equal in intensity, to two argand lamps, or ten mould candles.”

  [60] Our experiments produced 105 cubic feet, from one gallon of
  common whale oil.--_Note of the Author._

“The expence of an argand oil lamp, is usually admitted to be, about
three halfpence per hour. Now supposing ten candles to be burning, four
to the pound (two pound and a half,) they will cost 2_s._ 11_d._ of
which one-tenth part will be consumed in each hour. The cost of the
tallow light is then three pence halfpenny per hour.”

“If wax candles be employed, the expence of the light equal to an oil
gas burner for one hour, by the same mode of reckoning, allowing the
candle to burn ten hours, and taking the price of the wax candles, at
4_s._ 6_d._ per pound, will be about 14_d._”

“The comparative account will therefore stand thus:

  Cost of an Argand burner, supplied with oil gas, per hour    0³⁄₄
  Ditto of an Argand lamp, burning spermaceti oil                 3
  Ditto of Tallow mould candles                                3¹⁄₂
  Wax candles                                                    14

“These calculations on the cost of light from oil gas, are taken at the
usual price of good whale oil, but cheaper oils will answer the purpose
nearly as well, and as many of these are often to be procured, the whole
expence becomes materially reduced by their use.”


_Other products obtainable from Coal, namely:--Coal Tar--Pitch--Coal
Oil--Ammoniacal Liquor, and conversion of the latter into Carbonate, and
Muriate of Ammonia._

_Coal Tar._

The coal tar is so called from its resembling common tar in its
appearance, and most of its qualities.

This substance is deposited in the purification of the coal gas, in a
separate vessel destined to receive it. See fig. 3, plate I.

In the year 1665, Becher, a German chemist, brought to England his
discovery for extracting tar from coal, this distillation he performed
in close vessels. It is not mentioned in the records of the time,
whether Becher obtained, or rather collected, any other articles than
the tar.

Several works have been, at different times, erected both in England and
on the continent, to procure from coal a substitute for tar; but they
have turned out unprofitable speculations.

In 1781, the Earl of Dundonald invented a mode of distilling coal in the
large way, which enabled him not only to form the coke, but, at the same
time, to save and collect the tar. Even this process, however, for which
a patent was taken out, gained very little ground. Its object was too
limited; for though some of the proximate constituent parts of coal were
procured, they were obtained at an expence that nearly balanced the
profits; and no attention whatever was paid to the coal gas, which
constitutes by far the most valuable part obtainable from pit coal.

Coal tar is now used with advantage largely in the Royal Navy, and also
for painting and securing wood that is exposed to the action of air. The
wood being warmed, the tar is applied cold, and penetrating into the
pores, gives the timber an uncommon degree of hardness and durability.

The quantity of tar obtainable from a given quantity of coal, varies
according to the manner in which the decomposition of the coal is
affected. See page 122.

The tar obtained from Newcastle coal is specifically heavier than that
produced from cannel coal; hence it sinks in water, whereas the latter
swims on the surface of that fluid.

To render coal tar fit for use, it requires to be evaporated to give it
a sufficient consistence. If this process be performed in close vessels,
a portion of an essential oil is obtained, which is known by the name of

_Coal Oil._

To obtain this oil, a common still is charged with coal tar, and, being
properly luted, the fire is kindled and kept up very moderate, for the
tar is very apt to boil up in the early part of the process. The first
product that distils over is principally a brown ammoniacal fluid,
mixed with a good deal of oil. As the process advances, and the heat is
increased, the quantity of ammoniacal liquor lessens, and that of oil
increases, and towards the end of the distillation the product is
chiefly oil.

The oil and ammoniacal water which distil over do not mix, so that they
may be easily separated by decantation. The oil is a yellowish inferior
kind of naptha, which is very useful in painting ships, and for making
common varnishes. It has lately been employed as a substitute for whale
oil, to be burnt in out door lamps.

The contrivance by means of which this oil is burnt in lamps[61]
consists of a fountain reservoir to supply and preserve a constant
level. The burner with its wick is placed in the axis of the lamp, and
supplied with the oil from the fountain reservoir, placed on the outside
of the lamp. The air is admitted by an aperture at the bottom of the
lamp. The current of air in passing through the lamp envelopes the
burner and urges the flame, which is extremely bright; but it is
essential that the flame should be small. The draught tube proceeding
from the centre of the reflector above the flame carries away the smoke.

  [61] All the lamps on Waterloo Bridge, and the streets adjoining the
  bridge are lighted by means of tar oil.

1430 pounds of coal tar, produce 360 pounds of essential oil. The
residue left after the distillation is


If the coal tar is wanted to be converted into pitch, without obtaining
the oil which it is capable of furnishing, the evaporation of it may be
performed in a common boiler; but as it is extremely liable to boil
over, the greatest precaution is necessary in conducting the
evaporation. A spout or rim is added to the common boiler into which the
tar spreads itself as it rises, and by this means becomes cooled, and
the boiling over is checked.

1430 pounds of coal tar produce 9 cwt. of pitch. A subsequent
evaporation with a gentle heat, converts the coal pitch into a substance
greatly resembling _asphaltum_.

_Manufacture of Carbonate of Ammonia from the Ammoniacal Liquor of Pit

The ammoniacal liquor obtained in the gas light manufacture, is employed
for the production of carbonate of ammonia. The average quantity of this
liquor, obtainable from a chaldron, (27 cwt.) of Newcastle, or
Sunderland coal, amounts to from 180 to 220 pounds. It is chiefly
composed of carbonate and sulphate of ammonia. The quantity of ammonia
contained in it, varies considerably. The strongest liquor is obtained
from coal that readily cake, (page 45); a gallon (or eight and a half
pounds weight) of ammoniacal liquor usually requires for saturation,
from fifteen to sixteen ounces of sulphuric acid of a specific gravity
1,84. The weakest ammoniacal liquor is obtained from those species of
coal which do not cake, and which by a single combustion are reduced to
light ashes. It requires only from eight to ten ounces of sulphuric
acid, of the before mentioned specific gravity for its saturation.

The following process is employed in the large way, for obtaining
carbonate of ammonia from the ammoniacal liquor. To 108 gallons[62] of
the liquor contained in a cask, are added 125 pounds[63] of finely
ground sulphate of lime, which has been previously deprived of moisture
by heat. The cask is bunged up, and the mixture after being stirred
together for a few minutes, is left undisturbed for three or four hours.
Sixteen ounces of sulphuric acid are then added, the mixture is again
agitated, and is again suffered to stand undisturbed for four or six
hours. If the liquor be now examined, it will turn blue litmus paper,

  [62] One gallon of the strongest ammoniacal liquor, weighs eight and a
  half pounds.

  [63] This quantity is evidently too large, but the workmen assert,
  that an excess of sulphate of lime causes the carbonate of lime which
  is formed, to subside more readily, and the excess of sulphate of lime
  can do no injury.

In this operation a double decomposition takes place, the sulphate of
lime yields part of its sulphuric acid, to the carbonate of ammonia of
the liquor, to form sulphate of ammonia, and the carbonic acid of the
ammonia, combines with the lime of the sulphate of lime, to form
carbonate of lime, which falls to the bottom, the supernatant fluid
contains in solution, sulphate of ammonia.

When the liquor has become clear, it is pumped out of the barrel into
shallow cast iron boilers, where it is evaporated slowly. During this
process, a portion of sulphate of lime is deposited which is removed,
and as the liquor becomes more concentrated, part of the sulphate of
ammonia begins to crystallize and falls to the bottom. It is shovelled
out from time to time into wicker baskets, placed slanting over the rim
of the boiler, that the liquor which drains off from the crystals may
not be lost, and lastly the whole fluid is evaporated to dryness.

108 gallons of ammoniacal liquor from Newcastle coal, produce upon an
average, one and a half cwt. of dry sulphate of ammonia. To decompose
it, one cwt. is mixt with one quarter of a cwt. of finely ground chalk,
previously deprived of moisture by heat. The mixture is introduced (as
expeditiously as possible) into cast iron retorts,[64] heated nearly to
a dull redness, and when the lid of the retorts have been rendered air
tight, the fire is raised gradually till the retorts are of a strong red
heat. The carbonate of ammonia developed from the contents of the
retorts, is made to sublime into a leaden barrel-shaped receiver,
connected with the retorts, by means of a pipe four inches in diameter,
proceeding from the upper extremity of each retort, and opposite to the
mouth piece. The leaden receiver is furnished with a leaden cover,
fitting into a groove, where it is made air tight by lute. The receiver
which is supported upon a stand is provided at its base, with a small
pipe, furnished with a stopper. This pipe is left open till the liquid
products are got rid of during the sublimatory process. In the centre of
the cover, or at any other convenient part of the apparatus, is made a
small hole, slightly stopped with a wooden peg, to give vent to the
elastic fluid that becomes evolved during the process.

  [64] Of the usual form and dimensions, described page 58.

The time requisite for the operation depends on the mode in which the
retorts are set, the temperature kept up and other practical
circumstances. A charge of 120 pounds of the mixture of sulphate of
ammonia and chalk in one retort, is usually decomposed in twenty-four
hours. When the operation is at an end, and the receiver having become
cold, the cover is taken off, and the sublimed carbonate of ammonia
adhering to the sides of the receiver is detached by a chissel and
mallet, and after being freed from any casual impurities, is packed up
in stone jars for sale.

One cwt. of dry sulphate of ammonia, produces from sixty pounds, to
sixty-five pounds, of pure carbonate of ammonia. In some establishments,
the carbonate of ammonia is subjected to a second sublimation by means
of a gentle heat; but this is quite unnecessary if the process has been
conducted carefully.

_Manufacture of Muriate of Ammonia from the Ammoniacal Liquor of Coal._

It must be obvious that the ammoniacal liquor may be employed with great
advantage for the production of muriate of ammonia. For if the solution
of sulphate of ammonia obtained from the ammoniacal liquor by means of
sulphate of lime, as before stated, be mixed with common salt, (or any
other muriate) another decomposition takes place. The muriatic acid of
the common salt, unites to the ammonia of the sulphate of ammonia, and
produces muriate of ammonia, and the sulphuric acid of the sulphate of
ammonia, combines with the soda of the common salt, and produces
sulphate of soda, or glauber salt.

The liquor containing these two salts being evaporated, the glauber salt
begins to crystallize, and is removed from time to time. The evaporation
is continued till as much as possible of the glauber salt has been
separated, and the muriate of ammonia begins to crystallize on the
surface of the fluid in the form of a feathered star. The remaining
fluid is then run off into coolers, and deposits little else than
muriate of ammonia, till it gets below the temperature of 76° Fahr. at
which time the crystals are to be removed, lest they should be mixed
with glauber’s salt which now begins to be again deposited. After the
muriate of ammonia has been suffered to drain in baskets, it is heated
in shallow pans to drive off as much water of crystallization as
possible. It is then removed whilst still hot, into earthenware jars,
glazed within, and fitted with a cover, (having a hole of about half an
inch in diameter in its centre,) luted on with clay. The jars are put in
a cast iron pot over a strong fire, in a furnace capable of containing
from six to eighteen jars, surrounded with sand up to the edge of the
pot, and also having about two and a half inches of sand on the cover,
confined by an iron ring about three inches deep, and two inches less in
diameter than the cover, in order that if the luting should give way in
any part, it may be repaired without suffering the covers (which should
be kept during the sublimation at about 320° Fahr.) to be cooled by the
removal of a large portion of the sand.

These earthen jars may be filled to within two inches of the top, with
the dried salt gently pressed in, but not rammed close; and the fire
which has been lighted some time before, is now to be raised gradually
till the iron pots are of a pretty strong red heat all round, being so
placed by mean of flues in the furnace that the upper part may be first
heated, the bottom resting on solid brick work.

During the first impression of the heat, a portion of the salt carrying
with it a quantity of watery vapour not separated during the drying of
the salt, will escape through the hole in the cover, which must be left
open till all the aqueous part is exhaled: this is known by bringing a
piece of cold smooth iron plate near the hole, in order to condense the
sublimate, which becoming more and more dry, at length attaches itself
firmly to the plate, in the form of a dry semi-transparent crust.

At this time the hole is to be stopped with lute, more sand is to be put
on the cover, and the heat continued till it is judged that nearly the
whole of the muriate of ammonia is sublimed. The time requisite for this
purpose depends on the construction of the furnace, the size of the
pots, the briskness of the fire, and other circumstances only to be
learnt by experience.

The process should be stopped before the sublimation has entirely
ceased, as the heat in some parts of the jar may be too great when it is
nearly empty, and either by volatilizing a part of the salt itself, or
elevating a portion of foreign matter from which it can never be kept
wholly free, and thus giving the cake a yellow tinge, and a scorched,
opake, crackled appearance.

The same defects are likely to happen, when any part of the luting
having given way, is obliged to be repaired by wet lute, when the
sublimation is pretty far advanced: consequently glass vessels are
preferable, except on account of the expence, as they must always be
broken to pieces in order to get out the cake: the earthenware jars on
the contrary will serve for several sublimations, even the covers, if
well glazed, will last two operations. The sublimation being finished
and the apparatus having become sufficiently cool, the tops of the jars
are to be taken off, and the cakes of sal-ammoniac that are found
adhering to them are to be separated, and placed for a day or two in a
damp atmosphere, which softens their surface a little, and thus
facilitates the removal of any superficial impurities. Lastly, the cakes
are packed up in casks for sale.

The excise laws have hitherto operated strongly against the
establishment of manufactories of muriate of ammonia in England. Hence
an immense quantity of sulphate of ammonia obtained from the gas light
ammoniacal liquor, is exported from this country to the continent,
solely from the extreme rigour of the excise relating to the use of
common salt, and it is only this that has hitherto prevented the
establishment of manufactories of sal-ammoniac from the ammoniacal
liquor of the gas light process upon a large scale.

Chemical manufactories, of all others, will least bear excise, because
many of them are worked according to secret processes, which, if made
public, must pass into other countries; and the greatest part of the
profit ceases together with the export. The vexatious introduction of
excise officers into manufacturing laboratories, it is evident, puts an
end to all secrecy of operation. There are several chemical processes
which interruption will extremely injure, and others which it totally
destroys, and as on the whole they in general are of a nature in which
interference of others is most peculiarly vexatious, in all probability,
if the excise be extended to manufactures of this nature, it will
eventually put a stop to most of them, and greatly injure the revenue by
causing thereby to cease the duties which at present arise from the
exports and imports to a large amount, now depending on the chemical
trade of Great Britain.

We have now gone through all the improvements by which the gas light
manufacture has been distinguished during the interval which has elapsed
since the publication of our former work[65] on this subject; and
perhaps the reader may be inclined to think, from the extraordinary
height to which improvement has been carried in this art, that little or
nothing more remains to be desired with regard to it. Let it be
remembered, however, that the whole art is only in its infancy. There is
yet a wide field for improvement in the construction of the apparatus.
Ingenious men may speculate from what has been done, to what remains to
be effected, which no doubt will lead to objects of the greatest
utility, and most extended national importance.

  [65] A practical treatise on gas light.




  Elevation of the Revolving Gas Holder at the Westminster Gas
  Works                                                              181


  Gas Light Apparatus at the Royal Mint.

  Fig. 1, Perpendicular Section of one of the Horizontal Rotary
  Retorts with its Furnace                                           112

  Fig. 2, The Purifying Apparatus                                    150

  Fig. 3, The Tar Cistern                                            117

  Fig. 4, The Gas Metre                                              214

  The roof of the building surrounding the Gas Works is furnished
  with a projecting Louver to let out the smoke.


  Fig. 1, Represents a perspective view of a Portable Gas Metre      219

  Fig. 2, Perpendicular Section of the Horizontal Rotary Retorts at
  the Royal Mint Gas Works--at Chester--Birmingham, &c.              112

  Fig. 3, Perpendicular Section of the Gas Holder Valve and Siphon,
  or Water Reservoir                                                 222

  Fig. 4, Perspective View of the Governor, or Regulating Guage,
  for maintaining the Flames of Gas Lamps and Burners of an uniform
  intensity                                                          225

  Fig. 5, Plan of the Horizontal Rotary Retorts at the Royal
  Mint--Chester--Bristol--Birmingham--Kidderminster, &c.             115

  Fig. 6, Transverse Section of the Gas Metre at the Royal
  Mint--Chester--Birmingham, &c.                                     219

  Fig. 7, Perpendicular Section of the Gas Holder Valve              221

  Fig. 8, Front elevation of the Gas Metre, at the Royal Mint,
  shewing the registering train of Wheel Work                        218

  Fig. 9, Perpendicular Section of the Gas Holder, Governor, or
  Regulating Guage, at the Bristol--Birmingham--and Chester Gas
  Works                                                              171

  Fig. 10, Transverse Section of the Air-Box, and Lime Trough, See
  purifying apparatus                                                152

  Fig. 11, Perspective View of a Portable Governor or Regulating
  Guage                                                              232

  Fig. 12, Coal Tray of Horizontal Rotary Retort                     116

  Fig. 13, A jointed swing Bracket Lamp                              257

  Fig. 14, A Mercurial Universal Joint for Pendent Gas Lamps         256


  Fig. 1, Transverse Section of the Retort Ovens, at the Westminster
  and City of London Gas Works, showing the mode of setting and
  arranging Cylindrical Retorts                                       69

  Fig. 2, Longitudinal Section of the same                            69


  Fig. 1, Front elevation of the Retort Ovens at the Westminster and
  City of London Gas Works                                            69

  Fig. 2, Perpendicular Section of the Gas Holder, without Specific
  Gravity Apparatus, at the Birmingham Gas Works                     177

  Fig. 3, Plan of the same                                           177

  Fig. 4, Perpendicular Section of Mr. Malam’s Lime Machine          143

  Fig. 5, Plan of the same                                           146

  Fig. 6 and 7, Mouth Piece and Cover of cylindrical,
  parallelopipedal and semi-cylindrical Retorts, (exhibited fig. 1,
  plate IV,) drawn to a larger scale                                  71

  Fig. 8, 9, 10, 11, 12, and 13, Gas Lamps and Burners               253

  Fig. 14 and 15, Profile View and Section of Gas Mains, and mode of
  connecting them                                                    240

  Fig. 16, 17, and 18, Perpendicular Section of the
  parallelopipedal, ellipsoidal, and semi-cylindrical Retorts         53

  Fig. 19, 20, 21, and 22, Union Joint, and circular bends for
  connecting Gas Pipes                                               266

  Fig. 23, Test Apparatus for certifying the proper manner of
  working the Lime Machine                                           157


  Fig. 1, Plan, showing the Fire Place and Flues, of the Horizontal
  Rotary Retorts                                                     113

  Fig. 2, Longitudinal Section of the Collapsing Gas Holder, and
  the Tank of ditto                                                  189

  Fig. 3, Transverse Section of the same                             189

  Fig. 4, End View of the same                                       189

  Fig. 5 and 6, Horizontal plan shewing the mode of connecting the
  end plates of the Collapsing Gas Holder                            192

  Fig. 7, Perpendicular Section of the Gas Holder, without specific
  gravity Apparatus, at the Chester Gas Works                        175

  Fig. 8, Perspective View of the Revolving Gas Holder, at the
  Westminster Gas Works                                              181

  Fig. 9, Perspective View of the Reciprocating Safety Valve         196

  Fig. 10, Plan of the Purifying Apparatus, or Lime Machine, shewing
  the Air Trough of the Apparatus, with its axis and claws           152

  Fig. 11, Sliding part of a Pendent Gas Lamp, which may be raised
  or depressed                                                       257


  Exhibits an economical arrangement of a Gas Apparatus, for lighting a
  town, or large districts. The central building exhibits the Retort
  House. The roof is furnished with a projecting Louver to let out the
  smoke. The gable ends, and one side of the building, are of
  brick-work, the other side of the house is open, and supported on iron
  columns. The building to the right hand side of the Retorts, is the
  Purifying House, it contains the Lime Machine, page 149. The trap
  door, marked A, indicates the Cistern or Reservoir for receiving the
  Waste Lime. The third and smallest building in the design, serves for
  an Office of the Director of the Works. The front wall is represented
  as taken away, to show the position of the Gas Metre, the axis of
  which drives the agitating shaft of the Lime Machine. The axis of the
  Metre and the shaft of the Lime Machine, are for that purpose
  connected by a strap, (page 213.) The small building-on the left hand
  side of the Retort House, is a Smith’s Shop. T, shows the situation of
  the Main Gas Holder Valve (page 221.)



  Advantages of the art of procuring light by means of coal gas        1

  Air box of lime machine                                            153

  Ammoniacal liquor, quantity obtainable from a given quantity of
  coal                                                               303

  Ammoniacal liquor, quantity of sulphuric acid, required for
  saturating a given quantity                                        303

  Ammoniacal liquor, conversion of, into carbonate of ammonia        303

  Ammoniacal liquor, conversion of, into muriate of ammonia          303

  Apparatus for obtaining carburetted hydrogen gas from coal tar     285

  Apparatus for purifying coal gas                                   141

  Apparatus for certifying the proper mode of working the lime
  machine                                                            157

  Argand gas lamp                                                    253

  Argand gas lamp, quantity of gas consumed by different kinds       275

  Art of procuring coal gas, theory of                                33


  Bat’s wing gas burner                                              255

  Bends, for connecting gas pipes                                    267

  Burner, argand                                                     253

  Burner, bat’s wing                                                 255

  Burner, cockspur                                                   255

  Branch pipes                                                       239

  Branch pipes, dip of                                               243

  Branch pipes, mode of connecting                                   263

  Branch pipes, mode of proving                                      265

  Branch pipes, corrosion of                                         260


  Carbonate of ammonia, preparation of, from ammoniacal liquor of
  coal                                                               303

  Cement, for connecting gas mains                                   241

  Chandelier, sliding, for burning gas                               257

  Chester gas holder, description of                                 175

  Coal, analysis of, by destructive distillation                      35

  Coal, chemical constitution of                                      42

  Coal, classification of                                             41

  Coal, comparative facility with which different species are
  decomposed                                                         106

  Coal, chiefly composed of bitumen only, varieties of                42

  Coal, chiefly composed of bitumen, maximum quantity of gas
  obtainable from them                                                43

  Coal, containing more carbon than bitumen                           45

  Coal, containing more carbon than bitumen, maximum quantity of gas
  obtainable from them                                                48

  Coal, destitute of bitumen                                          42

  Coal, maximum quantity of gas obtainable from them                  44

  Coal, Gloucestershire                                               49

  Coal, Kilkenny                                                      44

  Coal, Lancashire                                                    44

  Coal, Newcastle                                                     47

  Coal, Scotch                                                       109

  Coal, Warwickshire                                                 109

  Coal, Welch Stone                                                   48

  Coal, Yorkshire                                                     44

  Coal oil                                                           300

  Coal oil, quantity obtainable from a given quantity of coal tar    302

  Coal tar                                                           298

  Coal tar, quantity obtainable from a given quantity of coal        122

  Coke, quantity obtained in the gas light process from a given
  quantity of coal, by means of cylindrical retorts                  132

  Coke, quantity obtained by means of horizontal rotary retorts      132


  Flue plan of setting cast iron retorts                              59

  Flue plan, report on a series of operations, made with retorts
  worked on the flue plan                                             61

  Fuel, minimum quantity required for the complete decomposition of
  coal, by means of cylindrical retorts                               61


  Gas, average cost of manufacturing it upon a large scale, in
  London                                                             106

  Gas, apparatus for lighting a town, best situation of, as far as
  it regards the most economical distribution of the pipes           249

  Gas, apparatus for lighting a town, arrangement of                 319

  Gas, apparatus for lighting a town, at the Royal Mint              112

  Gas, burners, different kinds of                                   253

  Gas, quantity of, evolved during different periods of the
  distillatory process employed for decomposing coal, in
  cylindrical retorts                                                 77

  Gas, observations on the progressive evolution of, during
  different periods of the distillatory process with cylindrical
  retorts                                                             79

  Gas flame, mode of regulating the magnitude of                     234

  Gas holder, construction of, originally employed                   164

  Gas holder, sheet iron, best adapted for it                        180

  Gas holder, sheet iron, best adapted for it, cost of               164

  Gas holder, sheet iron, lately adopted without specific gravity
  apparatus                                                          169

  Gas holder, at Birmingham without specific gravity apparatus       177

  Gas holder, at Bristol without specific gravity apparatus          175

  Gas holder, at Chester without specific gravity apparatus          175

  Gas holder, collapsing                                             185

  Gas holder, collapsing, rule for finding its capacity              195

  Gas holder, revolving at the Westminster gas works                 181

  Gas holder, collapsing, rule for calculating its capacity          185

  Gas holder, valve                                                  221

  Gas from coal tar                                                  286

  Gas from coal tar, average quantity obtainable from a given
  quantity of tar                                                    286

  Gas from oil                                                       289

  Gas from oil, quantity obtainable from a given quantity of oil     297

  Gas from vegetable tar                                             284

  Gas from vegetable tar, average quantity obtainable from a given
  quantity of tar                                                    284

  Gas illuminating power of                                          271

  Gas lamps                                                          253

  Gas lamps, diameter of the pipes for supplying them with gas       261

  Gas mains                                                          239

  Gas mains, mode of proving them when laid                          245

  Gas mains, observations on                                         247

  Gas mains, cost of a mile, laid under ground in London             252

  Gas mains, of pewter, lead, and tin, why unfit for distributing
  gas                                                                260

  Gas mains, weight of different lengths, of a given bore            251

  Gas metre, construction of                                         214

  Gas metre, construction of, at the Royal Mint Gas Works            214

  Gas metre, directions to workmen for fixing it                     229

  Gas metre, rule for calculating its power                          220

  Gas metre, at the Birmingham Gas Works, registering capacity of    220

  Gas metre, at the Bristol Gas Works, registering capacity of       220

  Gas metre, at the Chester Gas Works, registering capacity of       220

  Gas pipes, directions to workmen for adapting them to the
  interior of houses                                                 258

  Gasometer house, of sheet iron, of a given size, cost of           178

  Gasometer, tank of cast iron, of a given size, cost of             178

  Gasometer, tank of brick work, of a given size, cost of            178

  Gasometer, tank of wood, of a given size, cost of                  178

  Governor, or regulating guage                                      261

  Governor, its application and efficacy                             171

  Governor, directions to workmen for fixing it                      229


  Horizontal rotary retort. (See rotary retort horizontal)           110


  Lamps for burning coal gas                                         253

  Lamps for burning coal gas, quantity of gas consumed by different
  kinds, in a given time                                             275

  Lime machine originally employed, defects, and dangerous
  consequences to which it gave rise                                 141

  Lime machine, lately adopted                                       149

  Lime machine, at Birmingham gas works                              149

  Lime machine, at Chester gas works                                 149

  Lime machine, at Royal Mint gas works                              150

  Lime machine, capacity requisite for purifying a given volume of
  gas in a given time                                                157


  Mains for conveying gas                                            245

  Mains, average cost of a mile when laid in London                  252

  Mains, manner of proving them when laid                            245

  Mains, kind of, most economical for conveying gas                  251

  Mains, which do not supply branch pipes or lamps, observations on  250

  Mains, faulty, how distinguished                                   240

  Mercurial joint for pendent gas lamps                              256

  Muriate of ammonia, preparation of, from the ammoniacal liquor of
  coal                                                               303


  Newcastle coal, maximum quantity of gas obtainable from different
  kinds                                                               47


  Oven, for heating retorts, (See retort oven)

  Oil, from coal tar                                                 300

  Oil gas                                                            289

  Oil gas, quantity obtainable from a given quantity of whale oil    296

  Oven plan, of setting cast iron retorts                             67


  Pendent gas lamp                                                   257

  Pipes, directions to workmen for adapting them to the interior of
  houses                                                             258

  Pitch from coal tar                                                302

  Pitch, quantity obtainable from a given quantity of tar            302

  Purifying apparatus, (See lime machine)                            150


  Quicklime, best method of preserving it for the purification of
  coal gas                                                           160

  Quicklime, quantity required for purifying a given volume of coal
  gas                                                                162


  Reciprocating safety valve                                         196

  Regulating guage, regulator, or governor                       171 220

  Regulating guage, at Birmingham Gas Works                          177

  Regulating guage, at Bristol Gas Works                             177

  Regulating guage, at Chester Gas Works                             177

  Retorts, cylindrical cast iron                                      52

  Retorts, cylindrical, method of heating them by flues               59

  Retorts, cylindrical, experiments on setting three to one fire
  place                                                               61

  Retorts, cylindrical, experiments on setting four to one fire
  place                                                               53

  Retorts, cylindrical, cost of erecting them                         99

  Retorts, cylindrical, best mode of working them                     94

  Retorts, cylindrical, minimum quantity of fuel required for
  working them                                                        61

  Retorts, cylindrical, temperature best adapted for working them     94

  Retorts, cylindrical, conical                                       52

  Retorts, cylindrical, conical, comparative power of                 55

  Retorts, cylindrical, ellipsoidal                                   53

  Retorts, horizontal rotary                                         110

  Retorts, horizontal rotary, at the Royal Mint Gas Works            112

  Retorts, horizontal rotary, at Birmingham                          111

  Retorts, horizontal rotary, at Chester                             111

  Retorts, horizontal rotary, at Kidderminster                       111

  Retorts, horizontal rotary, action and management of               121

  Retorts, horizontal rotary, advantages of                          124

  Retorts, horizontal rotary, directions to workmen with regard to
  working them                                                       134

  Retorts, parallelopipedal                                           52

  Retorts, parallelopipedal, comparative power of                     55

  Retorts, parallelopipedal, best mode of working them                93

  Retorts, semi-cylindrical                                           53

  Retorts, oven, description of, at the Westminster and City of
  London Gas Works                                                    69

  Retorts, oven, experiments on                                       84

  Revolving gas holder, at the Westminster Gas Works                 181

  Revolving gas holder, rule for calculating its capacity            185


  Safety valve, reciprocating                                        196

  Self-acting guage, (see governor)                                  171

  Siphon                                                             221

  Sliding chandelier                                                 257

  South London Gas Works                                              69

  Spigot and faucit pipes                                            241

  Staffordshire coal                                                  44

  Swing bracket gas burner                                           257


  Tar, quantity obtainable from a given quantity of coal             130

  Tar gas, quantity obtainable from a given quantity of coal tar     287

  Tar gas, from vegetable tar                                        284

  Tar, retort                                                        285

  Temperature for working cast iron retorts, remarks on               94

  Test apparatus, for certifying the proper manner of working the
  lime machine                                                       157

  Theory of the production of gas lights                              39

  Towns lighted with gas                                             149


  Valve of gas holder                                                221

  Valve, hydraulic                                                   116

  Valve, of horizontal rotary retort                             116 124

  Valve, lime machine                                                156

  Valve, reciprocating                                               196

  Ventilation of rooms lighted by gas                                276


  Water reservoir, (See Siphon)                                      221

  Wheel work, registering of gas metre                               218


Of the most essential articles employed in the manufacture and
application of Coal Gas; delivered free of expence at any Wharf between
London and Vauxhall Bridge.

_Cast iron Spigot and Faucit Pipes._

                                                   £.    _s._ _d._
  1 and a half inch       5-sixths of an inch             2    6
  2 inches                3-eighths                       3    6
  2 and a half ditto        ditto                         4    0
  3 inches                7-sixteenths                    4    6
  4 ditto                 half an inch                    6    6
  5 ditto                   ditto                         9    0
  6 ditto                   ditto                        10    0
  7 ditto                   ditto                        11    0
  8 ditto                 5-eighths                      12    3
  9 ditto                   ditto                        16    6
  10 ditto                  ditto                        19    6

_Cast iron Flanch Pipes._

  1 and a half inch                                       3    0
  2 inches                                                4    0
  2 and a half inch                                       4   10
  3 inches                                                5    4
  4 ditto                                                 7    3
  5 ditto                                                 9    6
  Quadrant flanch pipes                                  14    0 cwt.
  Bend pipes of different radii, branch pipes and
  accommodating pipes                                    13    0 cwt.
  From eight to six inches 13_s._ 6_d._ from 5 to 3
  inches                                                 14    0
  Two, and 1 and a half inch                             14    6
  Siphon, water reservoir, or tar-well pipes, from 2
  to 6 inches in diameter                                15    0 cwt.
  Ditto, above 6 inches in diameter                      14    0
  Gas holder, or hydraulic valve pipes, with boxes       15    0
  Wrought iron work and screws to ditto                   0    7¹⁄₂ ℔
  Retorts of best picked iron, from second process       13    0 cwt.
  Mouth pieces to ditto, ground and fitted               20    0
  Wrought iron work and screws to ditto                   0    7¹⁄₂ ℔
  Connecting and stride pipes, ground                    20    0 cwt.
  Hydraulic cylinders                                    15    0
  Tapering pipes                                         15    0
  Outer fire doors                                       15    0
  Inner ditto                                            11    0
  Fire back, bearers, dead plates                        11    0
  Top, register, and slide dampers                       14    0
  Pullies, and friction sectors, turned and fitted       22    0
  Wrought iron gudgeons for ditto, turned and fitted      1    0 ℔.
  One inch bolts       }
  Seven-eighths ditto  } at                           0   0    5¹⁄₂ ℔.
  Three-quarters ditto }
  Five-eighths                                        2   8    0 gross.
  Half-inch                                           1  18  0 gross.
  Tar receivers and purifying vessels                 0  14  0 cwt.
  Condensing pipes, and inlet and outlet pipes for
  tanks                                               0  14  0
  Cast iron tanks put together complete, with bolts,
  screws, cement, &c.                                 0  16  0
  Gas holders, original construction, erected
  complete of sheet iron                              0  60  0
  Gas holder, collapsing ditto, complete, capacity
  30,000 cubic feet                                1000   0  0
  Gas holder, collapsing ditto, complete, capacity
  15,000 cubic feet                                 700   0  0
  Gas holder, collapsing ditto, complete, capacity
  22,000 cubic feet                                 800   0  0

_Wrought iron Gas Tubes screwed and fitted, warranted to bear a pressure
equal to a column of water 300 feet high._

     BORE.               PENCE PER FOOT.
  1 inch                       10
  7-eighths                     8
  3-quarters                    7¹⁄₂
  5-eighths                     7
  Half an inch and 3-eighths    6¹⁄₂

_Copper Tubes._

      BORE OF TUBE.                                PRICE PER FOOT.
                                                    £   _s._ _d._
     3-eighths of an inch copper tubes                   0    4¹⁄₂
     Half ditto             ditto                        0    6
     5-eighths ditto        ditto                        0    9
     3-quarters ditto       ditto                        0   11¹⁄₂
     7-eighths ditto        ditto                        1    4
     1 inch                 ditto                        1    8
     1 and a half ditto     ditto                        2    2

  Union joints 3-eighths of an inch 8_s._ half an
  inch 9_s._ 5-eighths of an inch 10_s._ 6_d._
  3-quarters of an inch                             0   14    0 per doz.
  Union T sockets, 3-quarters of an inch 20_s._
  half inch                                         0   14    0 per doz.
  Three-quarters of an inch main cocks              0    4    6 each

_Brazed sheet iron Tubes._

                           _s._  _d._
  3-eighths of an inch        0  3³⁄₄
  Half an inch                0  4¹⁄₄
  5-eighths of an inch        0  5
  3-quarters                  0  6¹⁄₂
  1 inch                      0  7¹⁄₂
  1 and a quarter             0 10
  1 and a half                1  3

                                                        £. _s._ _d._
  Ornamental gas lamp posts, and columns, fitted
  complete with York lamps glazed, tube, branches,
  cocks, and burners, ready for lighting            £. 6    6    0 each
  Or castings for ditto                                    13    0 cwt.
  Wrought iron work for ditto                               0    7¹⁄₂ ℔.
  Argand burners complete, from 2_s._ 6_d._ to              5    0 each
  Iron roofs for retort and gas holder houses,
  erected complete, at £. 6 6 0 per square of 100
  feet, superficial measure.

_Cost of laying cast iron Gas mains in London. To take up the ground, to
fill in, but not to re-pave the ground, and to drive two and a half
inches of lead into the joints of the pipes._

                            _s._ _d._
   3 inches                  1    6
   4 ditto                   1   10
   5 ditto                   2    1
   6 ditto                   2    2
   7 ditto                   2    4
   8 ditto                   2    7
   9 ditto                   3    0
  10 ditto                   3    4

                                                     £. _s._ _d._
  Tapping the mains and laying gun barrel, or
  branch pipes                                       0   1    0 per yrd.
  Governor complete to regulate every 24 hours
  30,000 cubic feet of gas                          60   0    0
  A lime machine, new construction, to purify
  30,000 cubic feet of gas every 24 hours          220   0    0
  A gas metre, to register 30,000 cubic feet of
  gas every 24 hours                               105   0    0
  A gas light apparatus complete, capable of
  producing 48,000 cubic feet of gas every 24
  hours, costs, if erected in London              8000   0    0

  ~A Gas Light Apparatus,~
  Capable of producing every 24 hours, a light equal to 21,330 tallow
  candles, eight in the pound, burning for six hours.

                                                            £. _s._ _d._

  Five horizontal rotary retorts, 12 feet 6 inches in
  diameter, complete for immediate use                   2320   0    0
  Two lime machines, ditto ditto                          536   0    0
  Two collapsing gas holders, 30,000 cubic feet capacity
  each                                                   2000   0    0
  A gas metre                                             200   0    0
  A governor or regulating guage                          100   0    0
  Tar well                                                 58   0    0
  Pumps                                                    67   0    0
  Connecting pipes                                        265   0    0
  Condensing pipes, between the retorts, tar well, and
  lime machines                                           219  16    0
  Retort house, with iron roof                            653  19    0
  Lime machine house, with ditto ditto                    230   0    0
  Workmen’s tools and sundries                            430   0    0
                                                      £. 7079  15    0

This apparatus is capable of producing every 24 hours, 66,000 cubic feet
of gas.


  C. Green, Printer, 15, Leicester Street,
  Leicester Square.

_In the Press_,







Exhibiting the general nature of Chemical Re-Agents or Tests--the
Effects which they produce upon different bodies--the Uses to which they
may be applied, and the Art of applying them successfully.


_Illustrated by a Series of Experiments._ _Price 9s._


Comprising a Series of curious and instructive Experiments in Chemistry,
which are easily performed, and unattended by Danger.

_The Fourth Edition._ _Price 9s._



Exhibiting a summary description of the Apparatus and Machinery best
calculated for illuminating Streets, Houses, and Manufactories, with
Coal Gas; with Remarks on the general nature of this new branch of civil

_The Fourth Edition._ _Price 12s._


_After the Method of Haüy_,


Exhibiting the Forms of Crystals, their Geometrical Structure, and
general Laws, according to which the immense variety of actually
existing Crystals are produced.

_Price 15s._


Intended to facilitate the Practical Analysis of Minerals, by pointing
out to the Student concise directions for performing the Analysis of
Metallic Ores, Earths, and other Minerals.

_Second Edition._ _2 Vols._ _Price 15s._



_Second Edition. Price 15s._

_Directions to the Binder._

Plate II, to face Title Page.

Plate III, IV, V, VI, and VII, at the end of the Book.

[Illustration: _Pl. III._


_in Explanation of Plate, II._

_Accums, Discription of Gas Works._]

[Illustration: _Pl. IV._

_Accums, Description of Gas Works._

_G. H. Palmer, Del._


_Westminster Station_]

[Illustration: _Plate V._

_Accums, Description of Gas Works._

  _Gas Holder at Birmingham
  without Specific Gravity Apparatus,
  capacity 30,000 Cubic Feet._

_W. Read, Sculp.^{t}_]

[Illustration: _Plate VI._

_Accums, Description of Gas Works._

  _Gas Holder at Chester
  Without Specific Gravity Apparatus,
  Capacity 30,000 Cubic Feet._

  _Gas Holder at Westminster,
  Without Specific Gravity Apparatus,
  Capacity 15,400 Cubic Feet_

_W. Read, Sculp.^{t}_]

[Illustration: _Accums, Description of Gas Works._

_Pl. VII._


_Lowry, Del.^{t} & Sculp.^{t}_]

  Transcriber’s Notes

  Inconsistent, archaic and unusual language, punctuation and spelling
  have been retained, except as mentioned below. The book uses a comma
  for decimal point as well as for thousands separator.

  The (minor) differences in wording between the Table of Contents and
  the actual text headings and the use of £ (with or without full stop
  and/or space) and _l._ have not been standardised.

  Depending on the hard- and software used and their settings, not all
  elements may display as intended.

  When relevant, texts have been removed from the plates and transcribed
  outside the plates.

  Plate II, 'Accums’': as printed in original work.

  Page xv, entry AMMONIACAL LIQUOR: there is no separate section for
  this material, but it is described in the first part of the section on
  Carbonate of Ammonia on page 303.

  Page 43, 'Pont Tops': possibly Pontops.

  Page 49, 'Tramsaren, near Kidwelly': possibly Trimsaran.

  Page 79, table: the quantities given add up to 556 cubic feet.

  Page 84, 'Enclosed are the result': as printed in the source document.

  Page 86, Expenditure of Process A: the amounts given do not add up to
  the total.

  Page 103/104, calculation: the numbers given do not add up to the
  first sub-total.

  Page 196, example of capacity calculation: the dimensions given result
  in a capacity of 22,500 cubic feet.

  Plate III, 'discription': as printed in the source document.


  Footnotes have been moved to under the paragraph where they are

  Tables printed over multiple pages have been re-combined into single
  tables; where relevant, items such as Carried Over etc. have been
  removed. The lay-out of the tables with financial analyses has been

  Several obvious minor typographical and punctuation errors have been
  corrected silently.

  Page iii: 'as its little expresses' changed to 'as its title

  Page x: entries for pages 80 and 81 moved to their proper place.

  Page xv: page number for entry AMMONIACAL LIQUOR changed to 303 (see

  Page 42, 'principle coal mines' changed to 'principal coal mines'.

  Page 43: 'Cowpers Main' changed to 'Cowper’s Main'.

  Page 143: 'Melam' changed to 'Malam'.

  Page 189, 'a fixed rigde point' changed to 'a fixed ridge point'.

  Page 218, '10,00,000 revolutions' changed to '100,000 revolutions'.

  Page 304: 'it will turn blue litmus, paper red' changed to 'it will
  turn blue litmus paper, red'.

  Page 312: 'sal-ammonia' changed to 'sal-ammoniac'.

  Index: Lines used as ditto marks and the word 'ditto' have been
  replaced with the dittoed words and phrases.

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