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Title: Experiments and Observations on the Following Subjects - On the Preparation, Calcination, and Medicinal Uses of - Magnesia Alba, etc.
Author: Henry, Thomas
Language: English
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    ON THE


    1. On the preparation, calcination, and medicinal uses of MAGNESIA

    2. On the Solvent Qualities of CALCINED MAGNESIA.

    3. On the variety in the Solvent Powers of QUICK-LIME, when
    used in different quantities.

    4. On Various ABSORBENTS, as promoting or retarding

    5. On the comparative Antiseptic Powers of VEGETABLE INFUSIONS
    prepared with LIME, &c.

    6. On the Sweetening Properties of FIXED AIR.



    _Utut tamen se res habeat, ego bona saltem fide
    tradam quæ hactenus rescivi omnia._



    Printed for JOSEPH JOHNSON, No. 72,

    St. Paul's Church-Yard.



  F.R.S. & S.A.


When I reflect how much the friendship with which you have favoured
me has contributed to my happiness; that from you has been imbibed
a considerable share of the small taste I possess for experimental
inquiries; and that to your skilful and affectionate treatment I am
greatly indebted even for the health I enjoy; it is impossible to
hesitate a moment in the choice of a patron: gratitude and esteem
direct me to inscribe this Treatise to you, and I chearfully obey their
dictates. If to these any additional motive had been wanting, I should
have received it from your having been an evidence to the result of
many of the experiments related in the following pages.

That your own health may long enable you to continue exemplarily useful
to your friends and to the public, is the sincere and ardent wish of,


  Your truly affectionate

  and very humble Servant,


  18th Jan. 1773.



A right composition of the several articles used in medicine, is of so
much importance to the practice of it, that every attempt to improve
or ascertain the method of preparing them, cannot fail of a candid
reception from the public.

Though great advancement has been made within these few years in
chemical pharmacy, by the labours of the very ingenious Dr. Lewis,
and some other writers on chemistry and the materia medica, there
is still a wide field left for improvement. It is to be wished that
Apothecaries, to whose province researches of this kind more peculiarly
belong, and many of whom are well qualified by a liberal education
to pursue them with advantage, would give their attention to these
material interests of the art: for while the several professors of
medicine and of surgery, are most laudably and assiduously employed in
adding to the enlargement of these sciences, why should the sons of
pharmacy remain supinely inactive, and leave every thing towards the
improvement of their profession to be performed by the members of the
elder branch of physic, instead of contributing _their_ share to its
support? as if tacitly acknowledging themselves unequal to the task,
and thereby incurring the too general, though unmerited, imputation of
want of knowledge and skill in their department.

The first part of the ensuing Treatise, which relates _an improved
method of preparing Magnesia Alba_, has been communicated to the
College of Physicians; and that learned body have done the author the
honour to insert it in the second volume of their TRANSACTIONS. It is
here reprinted as a proper introduction to the subsequent pages.

The calcination of Magnesia is not a new process[a]; but, as in this
state it is a medicine not much introduced into practice, perhaps a few
hints may be suggested, in regard to its medicinal and pharmaceutical
properties, which are not generally known; and it is hoped that some
useful information may be communicated relative to the various action
of absorbent medicines on the bile.

  [a] The German and Italian chemists formerly prepared Magnesia by
  evaporating the mother of nitre, and then calcining the residuum;
  but, Hoffman having discovered the method of precipitating it from
  the bittern remaining after the crystallization of sea salt, the
  calcination was disused, as tedious and unnecessary.

In the succeeding chapters, it is attempted to determine how far,
and in what proportion, lime promotes the solution of vegetable
astringents, and other drugs in water; and whether the action of
antiseptic medicines, thus dissolved, be in any degree impaired or
increased by this mode of obtaining tinctures from them.

In endeavouring to contribute to the determination of the question,
whether fixed air has the power of restoring sweetness to putrid
substances, the Author may at first sight appear to have transgressed
his proper limits; but, as fixed air, if possessed of this property, is
likely to be a valuable acquisition to the materia medica, he flatters
himself he shall incur no censure by the attempt.



  CHAP. I.                         Page

  _An Account of an improved Method
  of preparing Magnesia
  Alba._                              1


  _Miscellaneous Observations._      12


  _On the Medicinal Properties of
  Magnesia Alba._                    25


  _On the Calcination of Magnesia
  Alba._                             39

  CHAP. V.

  _On the Medicinal Virtues of
  Calcined Magnesia._                48


  _On the Action of various Absorbents,
  as promoting or retarding
  putrefaction._                     58


  _On the Solvent Qualities of Calcined
  Magnesia._                         80


  _On the various Solvent Powers of
  Quick Lime in different
  Quantities._                       88


  _On the comparative Antiseptic
  Powers of Vegetable Infusions
  prepared with Lime, &c._          105

  CHAP. X.

  _On the Sweetening Properties of
  Fixed Air._                       114


  _A Review of the general Conclusions
  deducible from the
  foregoing Observations and
  Experiments._                     135

  AN APPENDIX                       143


  Page 8, line 14, after _quantity_ read _of water_.
  Page 10, line 18, for _interrupt_ read _intercept_.
  Page 13, line 1, read _is there said_.
  Page 16, line 1, read _the other absorbents_.
  Page 29, note, line 4 from the bottom, for _albuminis_ read _aluminis_.
  Page 31, line 4, for _patients_ read _parents_.
  Page 83, line 9, after _elegant_ read _green_.
  Page 126, line 3, erase the _comma_ after _smell_.
  Page 127, line 3, place a _comma_ instead of the _semicolon_.



Although MAGNESIA ALBA is a medicine which has been in general use for
many years, yet the proper mode of making it is very little known. Our
_pharmacopæia_ affords us no information about it; and the _formula_
which is given by the Edinburgh College, as well as that with which
the ingenious Doctor Black[b] has favoured us, is deficient in several
circumstances. Hence the preparation of pure Magnesia has been confined
to very few persons, who have preferred the emolument they have
received by keeping their method secret, to the more diffusive utility
of which a publication of it would have been productive.[c] I therefore
beg leave to lay before the public a process for the preparation of
Magnesia, by which it will be in the power of every Apothecary to make
it himself, in all respects equal to that which is sold by those who
conceal their method.

  [b] Essays and Observations Physical and Literary, Vol. II.

  [c] Mr. Glass, a few years since, published an Essay on Magnesia Alba,
  in which all the information he affords us relative to the preparation
  is what we knew before, viz. that it is prepared from Epsom salts and
  pot ashes; and has related a number of difficulties which occur in the
  process, at the same time carefully, I had almost said meanly, avoiding
  giving the least instruction which might teach us how to shun them,
  though he has given a long detail of the many tragical consequences
  which may attend the use of Magnesia prepared under such disadvantages.

I am the more strongly induced to make this communication, because
the Magnesia which is generally to be found in the shops, is either
extremely coarse and ill prepared, or, which is still worse,
sophisticated with calcareous substances, differing greatly from true
Magnesia. I have been assured by some Physicians, that they have met
with it mixed with chalk, and even with lime, and I have sometimes seen
it so adulterated: a fraud of very dangerous tendency, as this powder
is so frequently administered to very young infants, and to adults of
tender bowels and costive habits.

This medicine was originally prepared abroad, from the liquor called
the _mother of nitre_, which is composed of a light earth united with
an acid; and these being separated, either by a strong fire, or by the
addition of an alkali, the powder was washed in water, and obtained the
name of Magnesia Alba. Hoffman afterwards prepared it from the bittern
remaining after the crystallization of sea salt, which he found to be
similar to the mother of nitre. And the factitious Epsom salt being
prepared from this bittern, and evidently composed of Magnesia and the
vitriolic acid, Dr. Black, who has favoured the world with a number of
very valuable experiments on this subject, made use of this salt with
success for the same purpose.

Happening some years ago to live in the neighbourhood of a gentleman
who has long been celebrated as the preparer of the most genuine
Magnesia, and never having been able myself to make Magnesia comparable
to his, by the commonly known methods, I was desirous of gaining some
intelligence as to his process, and was at last so fortunate as to
obtain some useful hints.

I availed myself of these, and after repeated trials, produced Magnesia
equally pure, white, tasteless, light and impalpable with that of Mr.
Glass; nay sometimes that of my own preparing has been superiour to
his, and in one respect has generally the advantage of it, namely,
that mine is not so stiff when dried, and may be reduced to the
finest powder by simple pressure; whereas _his_ requires some degree
of trituration to break the lumps effectually; which I imagine may be
owing to his pursuing Dr. Black's method of drying it, by straining and
_pressing_ out the water through a cloth.

The following is the manner of preparing it, which I have found

Dissolve any quantity of _sal catharticus amarus_, commonly called
Epsom salts, in its own weight of water; filter the liquor, and add to
it by degrees a filtrated solution of pearl ashes in an equal quantity
of water, stirring them gently until the mixed liquors have acquired
the appearance of a complete coagulum: then cease adding any more of
the alkaline lixivium; and, having diluted the precipitate, and mixed
it intimately with a small quantity of hot water, immediately throw
the mixture into a large vessel of boiling water. Keep it boiling for
a quarter of an hour, then take it out, and put it into glazed earthen
vessels. As soon as the powder has subsided, and before the water be
quite cold, pour it off, and add a fresh quantity of boiling water:
repeat these ablutions with several parcels of hot water, till the
liquor has entirely lost its saline taste. Then let it be so agitated
as to suspend the finer parts of the powder; in which state decant it
into other vessels, and having separated the water from the Magnesia
by inclination, put it on large chalk stones, till a considerable part
of the humidity be absorbed. Then wrap it up in sheets of white paper,
and dry it before the fire. Pour hot water on the remaining powder,
stir it, decant it in its turbid state, and separate the Magnesia from
the water as before. By these means, the whole, or most of it, will be
reduced to an equal degree of fineness.

The separation of the Magnesia will be promoted by heating the saline
lixivia before they are mixed; and the larger the quantity of water
into which the precipitated powder is cast, the more speedily and
perfectly will the vitriolated tartar, which is formed by the alkali
of the _sal catharticus_, be washed off. Dr. Black directs that three
or four times the quantity of water, to that of the solutions, should
be added; but this I have found greatly insufficient. The neutral
salt should be washed off as quickly as possible; otherwise, as he
justly observes, by allowing the mixture to stand for some time,
the powder concretes into minute grains, which when viewed with a
microscope, appear to be assemblages of needles diverging from a
point. These concretions cannot be redissolved by any washing, however
long continued. His intention, in boiling the mixture, is much better
answered, by adding it to the water when in a state of ebullition; and
once boiling in this manner is more effectual than a dozen washings in
hot water.

Much depends on the purity of the water used in the process. If it be
hard pump water, the selenites with which it is impregnated will be
decompounded, and the calcareous earth be deposited, after boiling;
which mixing with the Magnesia will render it impure, gritty and
discoloured. Rain water collected free from impurities, or clear
river water, are most eligible; but if the situation of the operator
does not permit him to procure these in a proper state, he should
either use distilled water, which has been kept till the empyreuma is
gone off, or at least such pump water as is free from any calcareous
or saline impregnation. When poured on the Magnesia, it should be
strained through a thick linen cloth, so as to intercept any accidental
impurities which it may acquire in heating.

The drying should be performed with expedition. To this end, the chalk
stones should be exposed to a moderate degree of heat; and when
they have been employed two or three times, should be dried before a
fresh quantity of the Magnesia is put on them. Cleanliness should be
particularly attended to through the whole process; and the vessels
ought to be carefully covered, that no dust may enter.

We may safely make use of a large copper brewing-pan, to boil the
Magnesia in; for as the acid is perfectly neutralized, there can be no
danger of its quitting the alkali, to which it has a greater affinity
than to the metal; and copper does not readily dissolve, even in acids,
when boiling hot; nor have I ever observed the least corrosion, though
I have frequently used such vessels for this purpose.



Since the drawing up of the paper which has been the subject of the
last chapter, some observations have occurred, which are either so
immediately connected with, or at least deduced from it, that it may
not perhaps seem inexpedient to introduce them in this place.

I was very much surprised to observe, in the Lectures lately published,
_as delivered_ by the very learned and ingenious Dr. Cullen, that
Magnesia is there said to be no more purgative than any other absorbent
earth. The sentence is this; (speaking of other absorbents) "Magnesia
alba should have been added to this set. It has had a considerable
reputation as an absorbent, and when neutralized, as a purgative; but I
find it is not more absorbent than any of the rest, nor more purgative
in less quantity, as chalk or crab's eyes given in the same quantity,
viz. dramij, will have the same effect. Therefore it may be neglected."

Surely this must have been an error of the person who wrote down the
lectures, and have escaped the notice of the ingenious editors; who,
from their skill in chemistry, must know that pure Magnesia differs
from every calcareous or testaceous earth with which we are hitherto
acquainted. These earths are nearly insoluble in the vitriolic acid,
and what part does unite with it, forms a selenitical salt, the most
difficult of solution of all others, and of an astringent nature:
whereas the Magnesia[d] united with the same acid, produces what is
commonly called Epsom salt, easy of solution, and purgative to the
bowels. The former, with the nitrous acid constitutes a calcareous
nitre, incapable of crystallization; with the marine acid a calcareous
muriatic salt; and when dissolved in vinegar, the mixture spontaneously
dries up into a friable sub-astringent salt: whereas Magnesia, with
all these acids, forms _purging salts_; that with the nitrous acid,
yellow, capable of being reduced into crystals retaining their form in
a dry air, but melting in a moist one: with the muriatic acid, a salt
is produced which does not crystallize, and easily melts when exposed
to the air: with distilled vinegar, a saline uncrystallizable mass is
formed, resembling glue both in colour and consistence while warm, but
becoming brittle when cold. Dr. Black says, that two drachms of this
salt purged a middle aged man four times; and half an ounce of the same
gave a woman of a strong constitution no less than ten stools.[e]

  [d] Essays Physical and Literary, Vol. II. p. 164.

  [e] Ibid. p. 64.

Besides, where an acid prevails, much smaller doses than two drachms of
Magnesia prove purgative; and it seldom happens that even that dose of
the other absorbents[f] will produce the same effect. Nor am I singular
in my opinion, when I declare my doubt whether Magnesia be not of
itself in some degree purgative, independent of its junction with any
acid whatsoever. It appears to be an earth _sui generis_. That of alum
resembles it in some respects, yet differs from it essentially, when
combined with the vitriolic acid: the alum is strongly astringent and
antiseptic, the Epsom salt purgative and septic.

  [f] Hoffman, having attributed the purgative quality of Magnesia to
  its forming a bitter cathartic salt with the acid it meets with in
  the stomach and bowels, adds, "At vero in contrarium quoddam dubium
  contra hanc sententiam moveri posse intelligo, quum nempe alia terrea,
  quæ prompte solvent et absorbent inhærescens primis viis acidum,
  neutiquam effectum laxantem exserant. Sed his regerere licet, quod
  interdum a pulveribus absorbentibus vel bezoardicis utique alvus
  fluidior fiat, si multum acidi primam regionem incolet: vis tamen eorum
  purgandi non tanta est, quanta magnesiæ, quia solutiones illorum cum
  acidis liquoribus factæ non tam eminente salino acri, sed moderate
  salso sapore imbutæ sunt, quam quidem ea, quæ ex magnesia et acidis
  liquoribus conficitur. Atque adeo ex eo apparet, præter alcali terreum
  aliud adhuc esse in magnesia principium, quod ad mixturam acidi in
  materiem stimulantem et purgantem transeat."

    Hoffman. Animadversiones et experimenta circa Magnesiam, &c.
    Op. Tom. 4. p. 480.

I have very lately seen a paper signed by Doctor Cadogan and dated in
the year 1767, in which he complains grievously of the advertisers of
Magnesia, making use of his name without his consent, and has published
the process for making _his_ Magnesia. The doctor's intent in this
was doubtless benevolent, but his manner of preparing this powder is
unnecessarily expensive and wasteful. He directs only one pound of
lixivium tartari to five pounds of sal catharticus amarus, which is
greatly insufficient to precipitate all the Magnesia. And he insists
strongly on the superiority of the lixivium prepared from salt of
tartar, to that made of potashes, as if the chemical effects of one,
were different from the other. But, says the Doctor, potashes render
the Magnesia bitter. Surely the vitriolated tartar produced by a union
of one vegetable fixed alkali with the vitriolic acid, is equally
soluble in water with that prepared with any other, and if so, will be
as easily washed off from the Magnesia.

But behold a champion steps forth, and at one blow levels to the
ground the whole tribe of Magnesia makers, who have procured it from
the factitious Epsom salts. I confess I have not had the happiness to
peruse this ingenious gentleman's pamphlet on the subject, but I have
formed a very extraordinary opinion of his _candour_, _modesty_, _and
knowledge_, from the very curious paper which he distributes with his
Magnesia. Notwithstanding Doctor Black, and since him Mr. Glass and
several others, have procured _pure_ Magnesia from the factitious Epsom
salts, Mr. Dale Ingram, assures us, that he has made an improvement,
"which is by the learned esteemed one of the greatest acquisitions to
the materia medica." And wherein does this mighty discovery consist?
even that Magnesia prepared from the waters of Epsom, is superiour to
that prepared from the bitter purging salt; and he assures us that the
Magnesia sold by him is so prepared.

To the first assertion I shall only reply, that every person at all
conversant in chemistry knows that Magnesia earth is the same, from
whatever substance it can be separated in a pure state; that the
factitious Epsom salt yields it in as great a degree of purity as the
salt of the Epsom water, and that Dr. Alston assures us, the artificial
salt "by various and repeated experiments, made in France as well as in
Britain, is demonstrated to be every way as good as, yea to be the very
same with, the genuine made of the Epsom waters."[g]

  [g] Alston's Materia Medica, Vol. I. p. 164.

As to the other declaration, it will be sufficient to observe that
one gallon of Epsom water contains only seven drachms of salt in a
dry season, and hardly six drachms in a wet one;[h] and that for this
salt to precipitate its Magnesia properly, it is necessary it should
be diluted with little more than its own weight of water.[i] Six
drachms of salt will yield two drachms of Magnesia. So that to procure
a pound of this powder Mr. Ingram must evaporate above sixty gallons
of the water, to between five and six pints, before he begins the
precipitation. Sure never did empiricism appear so thinly disguised!

  [h] Ibid.

  [i] Essays Physical and Literary, p. 163.

In the preceding chapter, the necessity of using water free from any
calcareous impregnation has been particularly insisted on, and I
have, on another occasion,[j] observed that great attention should
be given to the purity of the water used in the making of all the
saline preparations; and I may add in almost all the operations of
pharmacy. Dr. Percival, in his ingenious experiments on water, found
a quart of the Manchester pump water to contain upwards of sixty
grains of adventitious matter.[k] Suppose therefore, for instance,
that in making the extract from a pound of peruvian bark, it be
boiled only six times in the quantity of water directed by the London
Dispensatory, nine gallons will be consumed in the process; which
is a very moderate allowance, six coctions not being sufficient to
extract all the virtues of that drug. Dr. Percival boiled half an
ounce of bark twenty five times, in so many different pints of water,
the last of which had some impregnation, and the residuum gave a deep
colour, and considerable bitterness to rectified spirit of wine. If we
likewise suppose only one half of the foreign contents of such water
to be left by evaporation, then the quantity of calcareous and saline
matter, undesignedly mixed with the extract, will be two ounces and
two drachms, or nearly equal to the quantity of extract procured from
a pound of bark by pure water. Thus this important medicine becomes
grossly adulterated, without any such intention in the operator; and I
know it is the common practice to use pump water in making it.

  [j] Vide Percival's Essays, 2d. Edit. p. 321.

  [k] Ibid. p. 87.

I have particularly selected the Peruvian bark, as requiring a very
large quantity of water to extract the whole which it is capable of
yielding; but the proportion of water which I have here allowed, will
not be too great in obtaining extracts from most vegetable substances;
and how greatly not only the quantity, but the quality of the medicine
must be affected by the admixture of such a weight of insoluble
calcareous earth, is so obvious, that it is needless to expatiate on



The medicinal uses to which Magnesia has hitherto been applied are in
general so well known, that it will be necessary only to give a short
summary of the cases in which it is beneficial, for the information
of young practitioners, and of those of my readers who may not be
acquainted with medical subjects, this medicine being frequently
administered without the advice of a physician. If it should appear in
the subsequent part of this treatise that Magnesia is possessed of any
properties hitherto unsuspected in it, the sagacious reader will in a
great measure be left to draw his own practical inferences therefrom.

MAGNESIA ALBA is a powerful absorbent, and is given with great
success in disorders of the stomach and bowels arising from acidity.
This preparation had been introduced into the materia medica abroad
several years before it attracted the attention of our countrymen. The
celebrated Hoffman having strongly recommended it to the medical world,
some English practitioners began to prescribe it, and Dr. Cadogan
bestowing high encomiums on it, in his treatise on the nursing and
management of children, it soon made its way into general practice, and
supplied the place of the testaceous powders and chalk, which before
this period were the medicines usually given to correct acidities
in the primæ viæ. The acquisition of this medicine was of the more
importance, on account of its entire and easy solution in acids, and of
the purgative quality which it possesses; whereas the common absorbents
are apt to form concretions, and to induce costiveness; strong
objections to their free exhibition, as these properties render them
peculiarly unfit for the bowels of tender infants who are particularly
liable to diseases of this class.

This tendency to acidity generally attends children during the first
months and the time of dentition, and discovers itself when too
redundant by the green stools, sour vomitings, gripes and purgings
which it occasions: and as the nerves of children are extremely
irritable, spasmodic affections are often the consequence of this acrid
stimulus being retained in their bowels. In these cases Magnesia may be
administered in doses from five to twenty or thirty grains, according
to the age of the infant; and in proportion as it is intended to act,
either as an alterative, or as an easy purgative.

It has been a common practice to give Magnesia to children as a
preventive, and to mix it for this purpose with their food, in order
to correct that disposition which milk and the farinaceous aliments
have to turn sour. This however should be done with caution, for it
is only the excess of acidity which is prejudicial to infants,[l] some
degree of it is necessary; and should we too officiously and entirely
destroy, what we ought only to restrain within due bounds, we may
create disorders of an opposite nature to those we have endeavoured to
prevent, and instead of an acid, produce an alkalescent disposition
in the first passages. Indeed I fear that diseases have been more
frequently created than obviated by the use of preventive medicines,
and they should only be allowed in cases where the approach to disease
is manifest. But when a child is in a healthy state, the best means to
preserve him from a superabundant acidity, is to pay due attention to
the regulation of his diet, to give him proper exercise, not to confine
him too much in the foul air of hot unventilated rooms, to wash his
whole body every day in cold water, and to rub him very well night and
morning with a dry flannel, taking care that his stomach be not too
full at the time when this friction is performed.

  [l] Hactenus monstravimus, sicut cordis, musculorumque vires debiles
  erant, ita et solidorum quoque statum necessario imbecillem fuisse, et
  succos tenues, dilutosque; ut natura ampliationem vasculorum facilius
  efficeret, et incrementum animale minori cum molestiâ perageret.
  Sed ne status iste tonusque partium debilis laxusque ultra modum
  procederet (quod sæpe accidit, morbosque excitare solet) acidum quoddam
  juvenilium animalium stomachis datum est, quod quamvis aluminis
  instar, lac coagulat, atque ob eam causam aliquando morbum procreat,
  tamen fibrarum tonum astringet confirmatque, et putredinem omnem
  alkalinam, a qua alioquin periculum esset, reprimit. Quod quidem
  videri est, vel in coagulo stomachi vitulini, vel in aliis animalibus:
  sed istud tamen acidum, quod infantibus tarn idoneum est, redundat
  fortasse nonnumquam, et vel per testaceas pulveres, vel per medicamenta
  antiacida, ut supra dixi, corrigi debet.

    Russelli OEconomia Naturæ, p. 56.

Nor would I advise parents to rely with too much security on the
virtues of this medicine, where the disorders of their children
are complicated, or obstinate. The advice of the sagacious and
distinguishing practitioner will then be necessary to direct what
method of treatment is to be pursued. Nor can I here avoid lamenting
that the management of children when diseased, is so often in the hands
of nurses and ignorant women, from an absurd notion that their diseases
are not proper subjects of medical investigation; when in truth, there
are none which require a clearer judgement, a quicker penetration, or a
greater share of medical knowledge in the prescriber.

During the period between dentition and puberty, the diseases attendant
on a lax fibre still continue, though not so predominantly as in the
former stage; yet acescency is the manifest cause, or at least the
concomitant of many of the complaints to which children are at this
time liable. To this they are disposed, notwithstanding the change
in their diet to a more alkalescent kind, by the great quantities
of fruit, frequently crude and unripe, cakes, and other sweet and
greasy food with which they are too often indulged. By these errors
their bowels are overcharged, their digestion impaired, and the
aliment remaining too long in the stomach becomes sour, and occasions
vomitings, head achs, and other complaints which are often thought
to proceed from worms, and indeed are frequently attended with that
disorder; as the crudities thus generated in the bowels serve as a
nidus for these destructive vermin. Here likewise Magnesia may be of
considerable advantage as an alkaline purgative, neutralizing the
offending acid, and at the same time promoting its discharge by stool.
But if the stomach be overloaded with mucus or undigested aliment, a
gentle vomit ought to precede the exhibition of the Magnesia.

And even in a more advanced stage of life, persons of weak habits, and
who lead sedentary lives, are often afflicted with indigestion, sour
eructations, heart-burn, vomitings, and costiveness. These disorders
very frequently attend women during their state of pregnancy, and
are sometimes almost instantly removed by the use of Magnesia. Dr.
Watson[m] has published the case of a pregnant woman, who was afflicted
with such severe vomitings as to bring on convulsions, hiccoughing, and
violent pain at her stomach. What she brought up was acid, and so very
acrimonious, as to inflame and excoriate her mouth and throat; and the
great uneasiness she felt at her stomach upon swallowing any liquor
that had the least degree of acrimony, or was more than lukewarm, made
it probable that the internal surface of the stomach was affected
in the same manner. In this desperate situation, after a variety
of remedies had been tried in vain, the stomach was washed with
unsalted mutton broth, till the liquor was discharged without any acid
taste. Her pain was by this means abated, but in about two hours was
apparently returning with the same violence as before. This ingenious
Physician then directed a drachm of Magnesia to be given in mutton
broth, and to be repeated as often as her pain returned, without any
regard to the quantity the whole might amount to, supposing her pain
to continue severe. The first dose relieved her, and in three days she
took three ounces of Magnesia; and in the next three days, two ounces
more, by which time all her symptoms were removed. It is remarkable
in this case that a hypercatharsis was not the consequence of taking
so large a quantity of Magnesia, where there was so much acid to
neutralize it.

  [m] Medical Observations and Inquiries, Vol. III. p. 335.

In bilious habits, where there is generally a disposition in the
stomach contrary to acidity, Magnesia is usually esteemed to be
improper, taken alone: but I am dubious whether this opinion is well
founded, and many reasons for these doubts may be deduced from the
experiments hereafter to be recited. However, where putrid bile is to
be corrected and discharged, by stool, very good purposes may, perhaps,
be answered by taking the Magnesia, joined with a sufficient quantity
of acid to neutralize it, while in a state of effervescence; or by
swallowing the Magnesia and the acid, one immediately after the other,
so as to produce the fermentation in the stomach: for thus the fixed
air with which the Magnesia so greatly abounds, being let loose, may
powerfully correct the tendency to putridity in the contents of the
primæ viæ, and at the same time evacuate them downwards.

How far Magnesia may be of service in diseases of the skin I do not
take upon me to determine. Several authors have attributed cutaneous
eruptions, and indeed the ancient chemists ascribed almost all
disorders, to the presence of an acid in the blood; whilst others
absolutely deny that an acid can be admitted into the lacteals, or,
if admitted, exist in the blood in a state of acidity. In these cases
however, if an acid acrimony abounds in the stomach and bowels, with
a costive habit, and pale complexion, Magnesia will be a useful
corrector, and entering into the circulation in the form of a mild
neutral salt, may act as an excellent alterative,[n] proving both
diaphoretic and diuretic.

Having thus given a cursory detail of the medicinal properties of
Magnesia, in its natural state, I shall now proceed to consider it
in a state of calcination: but before any description of its uses in
medicine be given, it may be proper to take a view of the changes which
are produced in the nature of it by this operation.

  [n] Neque enim tantum absorbentem et catharticam, si acidum primâ in
  regione stabulatur, virtutem exserit; verum etiam si in remissiore
  dosi, ad grana xv. vel xx. usurpatur, diaphoreticum et diureticum
  effectum sequi, non semel observavimus.

    Hoffman. circa Magnesiam. Oper. Tom. 4. p. 481.



The free spirit of inquiry, and taste for experimental researches
which have of late so happily prevailed, have given rise to several
very important discoveries in the course of the last half century;
among which, those of the properties of the electrical fluid, and
of fixed air, hold a principal rank. That excellent philosopher and
experimentalist, the late Doctor Hales, first proved that most
bodies contain, as one of their component principles, a quantity
of air, differing from that of the common atmosphere in several of
its properties. The proportion of this element varies in different
substances, and in some constitutes nearly one half of their weight.
All calcareous earths, the testaceous powders, Magnesia and alkaline
salts contain it abundantly, and have the strongest affinity with it of
any bodies, except metals. From all these it is discharged by an acid,
and the stronger the acid is, the more sudden and plentiful is the
discharge of this vapour, which is of the same nature as that emitted
by fermenting liquors. Though it may be inspired in small quantities
with impunity, and, as appears from some late observations, even with
advantage in some cases,[o] yet it is a known fact that animals expire
sooner in a receiver filled with fixed air, than in vacuo. Lastly, it
is said to have the remarkable property of rendering putrid substances

  [o] The reader is referred for further information on this subject, to
  an excellent Treatise on the Management of Pregnant and Lying-in Women,
  lately published by my worthy and ingenious friend Mr. White; to a
  volume of Experiments and Observations, by Dr. Percival, which is now
  in the press; and to some very curious papers on factitious air, which
  have lately been communicated to the Royal Society, by Dr. Priestley.

In the precipitation of Magnesia, the acid of the Epsom salt uniting
with the alkali which is added to the solution, expels the fixed air
which the latter contains; but the vapour instead of being dissipated
as in the common effervescing mixtures of acids and alkalis, is quietly
and immediately absorbed by the Magnesia earth, to which it has a
strong affinity; and thus a double elective attraction takes place.

The very large proportion of this element contained in Magnesia Alba
has given Dr. Black an opportunity of throwing much light on this
hitherto obscure subject; and that excellent chemist has drawn such
inferences from the result of his experiments on Magnesia, Quick-lime,
and other alkaline substances, as are of the utmost importance to
chemistry. As this treatise may fall into the hands of several who may
not have an opportunity of perusing the valuable Essays in which these
experiments are contained, I shall take the liberty to make a short
extract from them, in order to elucidate the subject of the subsequent

The first object of Dr. Black's enquiry was, whether Magnesia could
be reduced to Quick-lime. To this purpose, he calcined an ounce of
Magnesia in a strong fire. When taken out of the crucible and weighed,
it had lost seven twelfths of its weight. Combined with different
acids, it formed salts of a similar nature to those constituted by the
same acids with the uncalcined powder; but dissolved in them without
the least degree of effervescence.

It slowly precipitated the corrosive sublimate of mercury, in the form
of a black powder; whereas before calcination a dark red precipitate
was formed from the same substance. Mixed with a warm solution of salt
ammoniac, it separated the volatile alkali from the acid; but it made
no separation of an acid from a calcareous earth, nor did it induce
any change upon lime-water; whereas in an uncalcined state, it rendered
quick-lime mild. Lastly, being digested for some hours with water, it
produced not the least alteration in the water.[p]

  [p] In making this experiment some time since, I imagined that Doctor
  Black had been mistaken in this point, and that some impurity in
  the water had prevented the success of his process, for I found the
  water impregnated, as I supposed, with the Magnesia. Flushed with my
  supposed success, I proceeded to make experiments on the lithontriptic
  powers of this water, which I found to be very considerable, acting
  more efficaciously on the human calculus, than either oyster-shell
  lime water, or a dilute solution of soap ley. I communicated this
  interesting intelligence to some of my medical friends; but on
  repeating my experiment several times with different parcels of
  Magnesia, that the truth of the fact might be absolutely ascertained,
  I at last was convinced, to my no small mortification, that what I had
  too sanguinely flattered myself to be a discovery likely to be highly
  serviceable to mankind, was founded on error; and that the properties
  communicated to the water proceeded from some calcareous matter which
  the Magnesia had received by being washed with impure water. I mention
  this as a caution to every young experimentalist, to be extremely
  careful in drawing conclusions. However, as something may be learned,
  even from an unsuccessful experiment, it proves that a very small
  quantity of lime is sufficient to impregnate a large quantity of water;
  for I used the calcined Magnesia, in the same proportion as lime is
  directed for making lime-water, so that very little of it could be
  quick-lime. And as oyster-shell lime water is a superiour solvent of
  the calculus to the water prepared with stone lime, is there not some
  reason to think that the calcareous earth, which has been dissolved in
  hard water, may, when calcined, be a more powerful lithontriptic, than
  either of the others? If any inference can be drawn from it, which may
  in the least promote the interests of mankind, I shall be sufficiently
  recompensed for the humiliating circumstance of recounting an erroneous

In pursuing his inquiries, he found that a very small portion of what
had been lost in the calcination was water, and that the other part
was fixed air, by the loss of which the Magnesia was deprived of its
power of effervescing with acids. And from hence the Doctor concluded,
that the change made in calcareous substances and in Magnesia by
calcination, was chiefly produced by depriving them of this air; and
that this volatile Proteus may be conveyed from one body containing it
to another body with which it has a greater affinity.

Thus lime being deprived of its air by calcination, and having a
stronger affinity with it than alkaline salts have, being mixed with a
lixivium of these salts, absorbs all the air from them, deprives them
of their property of effervescing with acids, and renders them more
acrid, at the same time that the lime becomes mild, and incapable of
impregnating water, but recovers its power of fermenting when mixed
with an acid.



Frequent objections have been made to the use of Magnesia Alba, on
account of the great quantity of air which enters into its composition.
Whenever it meets with an acid in the stomach they immediately unite;
but in forming this union, all the air contained in the Magnesia
is discharged with a great degree of effervescence, and recovering
its elasticity sometimes occasions very uneasy sensations in weak
bowels,[q] inflating and distending them overmuch, inducing griping
pains, and above all a sense of debility or sinking, which is not
easily described.

  [q] Neque tamen præterire possumus, id incommodi nos quandoque ab hoc
  Magnesiæ pulvere deprehendisse, quod flatulentias et morsicationes
  in imo ventri reliquerit, si videlicet frequentius in usum trahatur,
  primaque regio progignendis corrosivis succis, ut in hypochondriacis
  fieri solet, exposita sit.

    Hoffman. Oper. Tom. 4. p. 381.

My much respected friend Doctor Percival, who had often complained of
these disagreeable effects from the use of Magnesia, suggested to me
the idea of depriving it of its fixed air by calcination, having been
informed that they would be obviated by this method. Doctor Black
had indeed proved the practicability of the process, but he does not
appear to have made trial of the calcined Magnesia as a medicine.
In consequence of the above hint I calcined some Magnesia, and was
afterwards insensibly led to make further experiments, the event of
which, I hope, will be deemed of sufficient importance to apologize for
my communicating them to the public.


Eight ounces of pure Magnesia Alba were calcined with a strong fire in
an air furnace. Three hours calcination were necessary to discharge the
whole of the air from the Magnesia. When removed from the fire, it had
lost four ounces and three drachms of its original weight, and produced
no effervescence with acids; it had not acquired any degree of acrimony
to the taste, and when thirty grains of it were diluted with a few
spoonfuls of water and swallowed, it occasioned no uneasy sensation in
my stomach, nor sense of heat in my throat; proved nearly as aperient
as a double quantity of uncalcined Magnesia, and operated without the
least griping. It was remarkable that calcination had not reduced the
powder in bulk, in proportion to the diminution of its weight.

By the process of this experiment, Magnesia Alba is not only divested
of the disagreeable qualities which have been alluded to, but acquires
new properties which render it likely to answer some very important
practical purposes.

Doctor Macbride, who has with the greatest ingenuity and accuracy,
prosecuted the investigation of the nature of fixed air, discovered,
that a large quantity of it is discharged in the fermentation of
alimentary mixtures; and that the saliva being, in a healthy state,
void of air, acts as an absorbent of it, thereby moderating and
restraining the discharge of this vapour in the stomach. But when the
tone of that viscus is too relaxed to perform the digestion of the
aliment with proper vigour, or the saliva is diseased and corrupted,
the air expelled from the food becomes too elastic, and produces those
disorders which are commonly termed flatulent; and, perhaps, by its
effects on that prodigious plexus of nerves which is diffused over the
coats of the stomach, may sometimes occasion spasmodic or paralytic

It has been observed above, that calcareous earths, alkaline salts, and
Magnesia, being deprived of their air, attract it from every substance
with which it has a smaller degree of affinity. The two former becoming
highly caustic by the loss of their air cannot be administered but in
very small doses. But the calcined Magnesia being absolutely divested
of air, though not rendered acrimonious, and being able to absorb a
large quantity of this elastic flatus, may act more powerfully than
the whole tribe of carminatives, yet essentially differs from them in
many respects. _They_ contain a large quantity of air; _Magnesia_
in this state is entirely free from it; _Aromatics_ may be apt to
ferment, and increase acidities; the _calcined Magnesia_ is incapable
of effervescence, and powerfully corrects an acescent disposition in
the gastric juices; the _former_ constipate the belly; the _latter_ is

From this property of Magnesia, when calcined, of absorbing air,
it occurred to me, that it would of all others be the most proper
cathartic for patients labouring under the stone, who might be taking
the lixivium saponarium, having the advantage over all the vegetable
purgatives, which abound with air, and consequently have a tendency
to render the caustic alkali mild and inert. I even flattered myself
that it might coincide in promoting the efficacy of that powerful
solvent of the human calculus. Dr. Macbride's theory, that the lixivium
acts by depriving the calculus of its fixed air, appears to be well
founded; and Mr. Chittick in the exhibition of his nostrum, which,
notwithstanding all his empirical arts to disguise it, is now known
to have been the soap ley, kept his patients from every kind of diet
abounding with air. We may therefore venture to recommend it, though
not as a lithontriptic, being insoluble in water, yet as an assistant
to the lixivium, by absorbing a part of that air in the primæ viæ which
would otherwise be attracted by the caustic alkali, and thereby render
it incapable of acting on the calculus.

In all the diseases attended with an acescent disposition in the first
passages, in which Magnesia has been recommended in the third chapter,
the calcined powder may be given with superiour advantages, as it will
not produce any of those inconveniences, which have been attributed to
that medicine when uncalcined. Besides that it will act in a three-fold
capacity, viz. as an absorbent of air, and of acidity, and also as an
easy purgative. I know several persons who could never bear to take
the common Magnesia, with whom the calcined perfectly agrees. It seems
likely to be very serviceable in flatulent cholics, and I have been
informed of one very obstinate chronical case of that kind, which
was greatly relieved, though not perfectly cured by the use of it in
the Chester Infirmary, under the direction of a very judicious and
ingenious physician.

Even in gouty habits, joined with some warm aromatic, it may probably
be found useful in correcting the very great flatulency which so much
afflicts persons of this constitution; and perhaps the Cayenne pepper
would be the most proper addition to it, on account of the small
quantity of this spice that would be necessary to make the Magnesia
gratefully warm to the stomach.

It will appear in the succeeding chapter that calcined Magnesia is
strongly antiseptic: but I shall postpone my observations on that
subject till I have related the experiments which prove its claim to
that property.



The whimsical and ill-grounded hypotheses which were framed by the
chymists of the sixteenth century, had, unhappily, too much influence,
on the medical practice of that and the succeeding age. Among other
false theories which the physicians had adopted from them, was that of
attributing the origin of most diseases either to an acid or alkaline
cause: but the former, being more obvious to the senses, was supposed
to be the most frequent parent of diseases. Among others, fevers,
even of the putrid kind, were imagined to be occasioned by an acid,
and from hence the testaceous medicines acquired so high a degree of
reputation, as to be deemed the grand correctors of acrimony, and were
almost universally prescribed as alexipharmics; and the most celebrated
compositions which are ranged under that head, contain a large
proportion of these powders.

But a very learned physician, by a series of accurate and ingenious
experiments on septics and antiseptics, has proved that chalk and all
the testaceous powders accelerate the corruption of animal flesh, and
from the result of one he made on bile with crab's eyes, he naturally
concluded that all these substances would produce the same effect on
that humour, as they had all uniformly proved septic to flesh. Yet,
even upon this supposition, he candidly allows, that in some fevers,
they may have their uses, even where no offending acid exists; as
in order to cure some diseases, it may be requisite to attenuate
the humours, and relax the fibres by a degree of putrefaction, and
that possibly the crisis of fevers of this kind, may be hastened or
perfected by the testaceous powders. In diseases, however, where the
disposition to putrescency is already too strong, all medicines, which
in the smallest degree increase such tendency should be studiously
avoided; and, on this account, the administration of the testacea in
putrid, malignant fevers has of late been condemned by some ingenious
writers. I was myself fully convinced of the rectitude of this opinion,
and, in drawing up an account of the medicinal uses of Magnesia,
had therefore suggested the impropriety of prescribing them where a
bilious acrimony prevails. But not being able to recollect, that the
septic powers of Magnesia had ever been experimentally proved,[r] I
thought it would be most satisfactory to determine them by that method;
little doubting but that the event would justify my doctrine. My
inquiries evince the accuracy with which Sir John Pringle has made
his experiments, but as I was induced to carry the investigation of
this subject further than he has proceeded, very different practical
inferences, from those I at first expected, may, perhaps, be deduced

  [r] I at that time overlooked an experiment of Dr. Macbride's which
  proves Magnesia to be septic to _animal flesh_; but having met with it
  just before these papers were going to the press, I take this method of
  acknowledging it.


Two drachms of fresh beef, two scruples of Magnesia, and two ounces
of distilled water were mixed in one bottle; and in another the same
quantity of beef with two ounces of distilled water only: the meat
was cut small, and the bottles were placed uncorked in a heat rather
inferior to that of the human blood. In twenty four hours the beef in
the mixture with Magnesia was become quite putrid. The standard was
perfectly sweet, and remained for some days, before it acquired the
true putrid foetor.

Being thus convinced that Magnesia is possessed of the property of
hastening the putrefaction of animal flesh, in common with the rest
of the absorbent tribe, it was imagined, that it might be of some
consequence to practice, to determine how far it exceeded or was
inferiour to the calcareous and testaceous earths as a septic; and also
whether calcination produced any difference in it, in this respect. In
reciting the experiments, where I only mention _Magnesia_, I always
would be understood to mean that powder in its uncalcined state, the
calcined shall constantly be distinguished by that epithet. It also
appeared to be a convenient opportunity of repeating the inquiry, how
far the addition of the testacea might take effect in diminishing the
antiseptic qualities of the contrayerva root.


Into one phial were put two scruples of Magnesia, into a second the
same weight of calcined Magnesia, and into three others the same
quantity of chalk, _pulv. e chel. cancr. comp._ and _pulv. contrayerv.
comp._ To each of these, two drachms of fresh beef, and two ounces of
distilled water were added. A sixth phial was kept as a standard, and
contained only the same proportions of beef and water. The bottles,
distinguished in the order they are mentioned by the numbers 1, 2, 3,
4, 5, and 6, were placed in the same heat as that to which the Magnesia
was exposed in the former experiment, and were frequently shaken up and

In twelve hours, number 1 began to smell; an intestine motion was
perceptible in numbers 3, 4, 5, and 6, but especially in the chalk. In
twenty-four hours, number 1 was become highly putrid, number 3 smelled
offensively, number 4 had acquired a very slight foetor, as had
number 5 which fermented briskly. The standard had acquired a vinous
smell, but number 2 remained unchanged.

In thirty six hours, number 3 was very putrid, numbers 4 and 5 had
made little progress since the last examination, though number 5
was rather more putrid than the other, allowance being made for the
peculiar odour of the contrayerva; but in four hours more they both
stunk intolerably. The standard continued two or three days longer
before it became absolutely putrid, and the calcined Magnesia preserved
the beef untainted for several days longer, when it was removed to make
room for other phials. The water which was mixed with the calcined
Magnesia differed from all the others in not becoming bloody, nor did
the beef in it seem so tender as when infused in lime water.

When I made the first experiment, I had not observed any discharge of
air from the Magnesia and beef, and in the present one no fermentation
was perceptible either in number 1 or 2. As this was an unexpected
circumstance in the former, I repeated the experiment several times,
but the event was always the same.

Magnesia was afterwards compared with crab's eyes, burnt hartshorn, and
prepared coral. The mixture with Magnesia grew putrid first, afterwards
that with the crab's eyes; the other two remained for some hours longer
before the putrid foetor came on.

From the above experiments it appears that Magnesia Alba, when replete
with fixed air, is a stronger septic to animal flesh than any other
absorbent which was compared with it; and yet when deprived of its air
by calcination, it powerfully resists putrefaction. Dr. Macbride has
endeavoured to account for this difference between calcareous earths
and quick-lime, by supposing the particles of the lime to insinuate
themselves intimately into the texture of the beef, and to prevent
the escape of the fixed air, by attracting, absorbing, and thus
confining it within the substance of the beef. How far this theory
is satisfactory is not my province to determine; and the matter is
so obscure, that I do not presume to offer any conjecture of my own,
relative to the reason of it.

Nitre is found to be a strong antiseptic when applied to animal flesh,
but to resist the putrefaction of bile with a very disproportionate
force: and Dr. Percival has lately observed the same difference in
the action of the Columbo root. These variations encouraged me to
try the effect of Magnesia on gall; but being strongly prepossessed
with the notion of its septic quality, I entertained very small hopes
of a different event. I was also desirous to compare the action of
the calcined Magnesia with the other. The heat used in the succeeding
experiments was the same as that in the preceding trials.


To two drachms of fresh ox gall, were added two scruples of Magnesia,
and two ounces of water, in one phial. Two scruples of calcined
Magnesia with the same quantity of gall and water were placed in
another; and a third containing two drachms of bile without any other
addition than water, served as a standard, which began to have a rank
smell in forty-eight hours, and in sixty hours was highly offensive.
The calcined Magnesia and bile emitted a sweetish smell, something
resembling that of the urine in a diabetes: the liquor which swam above
was quite pellucid and colourless, whereas that of the other Magnesia
was turbid and tinged green with the bile. Both were perfectly free
from any putrid foetor; the latter continued so for ten days, and
the bile with the calcined Magnesia remained unchanged as long as any
notice was taken of it.


Twenty grains of Magnesia preserved six drachms of ox's gall free
from any signs of corruption for twenty-four hours after the standard
containing gall and water, of each six drachms, had become putrid. A
scruple of the calcined Magnesia mixed with the same proportions of
gall and water, remained without any alteration as long as they were
attended to, which was about ten days.


The putrid liquor which had been used as a standard in the fourth
experiment, was divided into four parts, one of which was continued
as a standard, to another was added about half a drachm of Magnesia,
and an effervescence was procured by some drops of oil of vitriol.
The offensive smell continued for a few minutes, but was soon much
abated, and at length entirely sweetened. To another portion was added
twenty grains of Magnesia only, this in fifteen minutes had almost
lost its putrid smell, and in two or three hours became quite sweet.
To the fourth was added the same weight of calcined Magnesia, which
almost instantly deprived the liquor of every degree of putridity. The
standard was then mixed with a scruple of crab's eyes, which, for about
a minute, seemed to diminish the foetor, but it then returned as
strongly as ever; whereas the others continued sweet for several days.


Two drachms of putrid bile, which had been kept closely corked in a
phial since the year 1770, and smelled very offensively, were mixed in
a cup with twenty grains of Magnesia, and half an ounce of water, and
thereby restored to sweetness. Twenty grains of calcined Magnesia were
also added to two drachms of the same bile: on stirring them a pungent
smell was observed, like that of volatile salts, and half an ounce of
water being put to the mixture, the bile was totally deprived of any
putrid smell. Even five grains of the same powder sweetened two drachms
of putrid gall.


Magnesia, calcined Magnesia, chalk, crab's eyes, _pulv. e chel.
cancr. c._ and _pulv. contrayerv. comp._ each in the proportion
of two scruples to two drachms of ox gall and two ounces of water,
were exposed to the usual warmth. The crab's eyes mixture grew rank
in twenty-four hours, and in forty-eight was absolutely putrid: the
bile with the chalk was in the same condition in twelve hours more.
The Magnesia mixture became putrid on the ninth day; the _pulvis e
chel._[s] on the tenth; but the _pulvis contrayerv. comp._ preserved
the bile from corruption about three weeks, and no change was
perceptible in that with the calcined Magnesia when examined above a
month after their first admixture.

  [s] Doctor Macbride found that _pulv. e chel. c. c._ hastened the
  corruption of bile: might not this depend on some variety in the
  composition of that powder? Chalk and oyster shells are often
  substituted in the hospitals and by the druggists, for the other


Twenty grains of Magnesia, and the same quantity of chalk, were
separately neutralized with distilled vinegar, and their effects on ox
gall compared with that of thirty grains of the artificial Epsom salt
dissolved in a sufficient quantity of water. The bile in this solution
became putrid in about sixty hours. That in the solutions made in the
vegetable acid retained its sweetness for several days longer.

These experiments, which terminated so very differently from what I had
expected, seem to justify, in some degree, the practice of giving the
testaceous and absorbent medicines in fevers of a putrescent type, at
the same time that they point out some of that class which ought to
be avoided, and evince how fallacious a method it is to judge of the
effects of medicines _a priori_.

As the bile is, by many, supposed to be the great source of putrid
diseases, ought not the antiseptics which may be prescribed in these
cases, to be such as more particularly impede the corruption of this
fluid, rather than that of flesh?

On account of the superiour antisepticity of the calcined Magnesia
to most of the absorbents, and its greater purity and solubility,
together with the probability of its acting as an evacuant, as well as
a corrector of putrid bile, does it not appear to merit a preference
to all other medicines of this class?

In diseases where an acid cacochymy prevails, and an alkalescent diet,
such as wild fowl, fish, &c. is prescribed, but from the scarcity of
these articles in some countries, cannot be complied with; may not
taking Magnesia or the testaceous powders, immediately before or after
meal time, coincide with this intention, by increasing the putrefactive
fermentation of other animal food in the stomach, which in these
disorders is almost totally subdued by the superabundant acid?

But where animal food is used in putrescent diseases, either through
necessity, or the obstinacy of the patient, ought not Magnesia, in an
uncalcined state, and all the calcareous and testaceous earths to be
carefully abstained from?

Dr. Percival, in a volume of very ingenious experiments and
observations which have been before referred to, has mentioned a
physician of his acquaintance, who always observed his stools to be
more particularly offensive after having taken Magnesia. Might not
this proceed from the action of the Magnesia on the animal food he had
eaten; and is it not reasonable to suppose that the effect might have
been very different where a vegetable or milk diet had been used, as is
generally the case in putrid fevers, and in young children?

I know a person whose stools are, in common, very little tinged with
bile, who after taking calcined Magnesia, evacuates fæces of a very
bilious appearance, though less foetid than usual. It is a fact
worthy of observation, that in the experiments which were made with
calcined Magnesia and bile, the latter was absorbed by, and had united
with the former; and another remarkable circumstance was, that the
watery part of all the mixtures which resisted putrefaction, acquired a
very pungent, saline taste.



Dr. Macbride, whose experimental researches have very justly acquired
him a high degree of reputation in the philosophical world, supposes
fixed air to be the combining principle of bodies, and has applied
this ingenious theory to pharmaceutical improvements. He discovered
that lime triturated with resinous gums, promotes their dissolution
in water; which, he thinks, is thus enabled to take up the same parts
of these substances, as are soluble in spirit of wine. These aqueous
tinctures are transparent, not milky like the solutions made with yolk
of egg, or gum arabic; but the lime communicates a highly disagreeable
taste to them, and the action of lime water, which he used in some
instances, is not sufficiently powerful to extract strong tinctures
from these bodies. As calcined Magnesia has a great affinity with fixed
air, I was desirous of trying whether it would contribute to render
resinous substances soluble in water; for being itself insoluble, the
solutions would consequently be free from any other impregnation than
that of the resins.


Five grains of camphor were rubbed for five minutes with an equal
quantity of calcined Magnesia: after the camphor was reduced to powder,
it united into a hard concrete with the Magnesia, but immediately
dissolved on the addition of a small quantity of distilled water, of
which an ounce was mixed with them, and immediately passed through
filtering paper. The filtrated liquor was highly impregnated with the


Five grains of opium triturated in the same manner, yielded a
transparent tincture, of as deep a colour as the tinctura Thebaica of
the London Dispensatory, and tasting strongly of the opium.


Gum guaiacum and calcined Magnesia, of each a scruple, being rubbed
with an ounce of water, and filtered, gave an elegant green tincture,
quite transparent, and possessing, in a considerable degree, the taste
of the gum.

Gum galbanum, storax, mastick, myrrh, assafætida, scammony and balsam
of Tolu, being severally triturated with equal weights of calcined
Magnesia, diluted with water and filtered, afforded neat tinctures,
strongly impregnated with the different drugs.


In order to determine the quantity of opium thus dissolved, half an
ounce of crude opium, the same quantity of calcined Magnesia, and eight
ounces of distilled water were rubbed for a quarter of an hour in a
glass mortar, and having stood to infuse during two hours, the liquor
was separated through paper. The tincture was of a darker colour than
that before described, and was reduced by a gentle heat to a pilular
consistence. This extract weighed sixty-eight grains, which, allowing
for impurities, for what would be dissipated in evaporation, and for
the air probably absorbed by the Magnesia, is a large proportion to be
so soon dissolved. The residuum which was left in the filter was dried,
and weighed six drachms.


A drachm of Peruvian bark, twenty grains of calcined Magnesia, and four
ounces of distilled water being rubbed together during fifteen minutes,
the filtered infusion resembled in appearance the simple tincture
of bark, and had an intensely bitter taste, but was not strongly
impregnated with the peculiar aroma of the bark.

Thus then we have an easy and very elegant method of preparing
aqueous tinctures from the gum resins, and administering them in a
more convenient form and in larger doses than could be done when
dissolved in a spirituous menstruum; and much more agreeably than in
the half-dissolved state to which they are reduced by the aid of egg
or gum arabic. The Magnesia does not impart any thing to them, whereas
the lime will seldom be so saturated with air but that some part of
it will remain soluble in the water: and as they may be given diluted
to whatever degree the prescriber chuses, considerable advantages may
be expected therefrom, it being probable that they will be better
enabled to pervade the very small vessels; and the heating properties
of the balsams be more effectually obviated than by any other mode of

Indeed, tinctures prepared by the above method, are not calculated for
officinal compositions, but for extemporaneous prescription; as most of
them, except camphor, deposite a sediment when they have been kept a
week or two.



The difficulty of solution in the vegetable astringents has been
complained of by various writers on the _Materia Medica_. Water and
alcohol are the menstrua in use; but great quantities of each are
necessary to procure even a slight impregnation, and much heat and
long boiling are said actually to destroy the astringent quality, and
vegetable texture.[t] As a menstruum capable of dissolving them with
greater facility appeared to be a desideratum, not only in pharmacy,
but in other arts, particularly in that of dying blacks, I resolved to
try Dr. Macbride's method of increasing the solvent power of water, by
means of quick-lime. But as I was aware that the quantity of lime he
made use of in obtaining an aqueous tincture of Peruvian bark, would
be too great for the dyer's use, I wished to use only such a quantity
as would be sufficiently saturated with the air contained in the
vegetable, to be itself precipitated; and to compare the tinctures thus
made, with a standard prepared with simple water.

  [t] Vid. Lectures on the Materia Medica, as delivered by William
  Cullen, M.D. p. 195.


I rubbed three drachms of Aleppo galls reduced to powder, with four
ounces of filtered rain water, for fifteen minutes, and then passed
the solution through paper. It was very styptic to the taste, and was
nearly of the same colour as Huxham's tincture of bark. The residuum in
the filter was unchanged in colour. The bottle containing the liquor
was marked number 1.


Three drachms of the same galls, and two scruples of quick-lime, were
triturated with four ounces of rain water, as in the last experiment.
The filtered liquor had scarcely any astringency to the taste, and was
of a very pale colour. The residuum was of a deep purple. Marked number


The same quantity of galls as in the two former experiments, after
triture in the same degree with four ounces of lime-water, was
separated by filtering through paper. The tincture thus obtained was
highly astringent to the palate, of a deep chocolate colour, and the
residuum was of a lighter brown than number 1. Marked number 3.


To each of the above tinctures were added forty drops of a strong
solution of sal martis. Number 1 became very black. Number 2 changed
colour but little, and on standing precipitated a brown sediment,
which, the superiour part of the liquor being decanted off, became
again transparent on the addition of a few drops of the vitriolic acid.
Number 3 appeared to strike a deeper black than number 1; and these
being tried as inks, number 3 seemed to have the superiority; but a
slip of linen cloth being macerated in each for some hours, that in
number 1 had taken a more perfect black than the slip number 3. No
trial was made with cotton or woollen, which it is probable would have
differed from the linen.


Oak bark was used instead of galls, with similar success, except that
the infusion made with lime-water was not so deep in colour as that
with simple rain water, though much deeper than that prepared with


Peruvian bark, quick-lime, and lime water, in the same proportion as
directed by Dr. Macbride, were rubbed together. The filtered infusion
had little colour, tasted very slightly of the bark, though strongly
of the lime, and on my blowing in a stream of air from my lungs, the
surface of it was immediately covered with a cremor calcis, the liquor
grew turbid, and deposited a copious sediment.


The same quantity of Peruvian bark, and of lime water, without the
addition of any fresh lime, being rubbed in the same manner, afforded
a tincture tasting strongly of the bark, nearly of the same colour
as the simple tincture obtained by proof spirit, and retaining its
transparency when blown into. This tincture was much more strongly
impregnated than one made by triture with common rain water only. And
by this process, allowing a few hours for maceration, an infusion is
prepared, greatly superiour in strength to any decoction, infusion, or
tincture of bark I ever saw.

From the result of these experiments I suspect, that by using a
greater quantity of lime in the sixteenth and twentieth experiments
than the vegetable could saturate with fixed air, the water became so
impregnated with lime as to be more unfit to act on the vegetable.
From the purple colour of the residuum of number 2, it was evident
that the galls were decompounded, but the water was not capable of
dissolving and suspending the particles. Dr. Percival[u] mentions his
having unsuccessfully repeated Dr. Macbride's experiment with bark and
quick-lime. To what then can this difference be owing? Perhaps it may
be accounted for thus: It seems probable that the lime used by Dr.
Macbride, not being fresh calcined, had recovered part of its air; for
he says, "It will no doubt be reckoned superfluous, that lime water is
ordered to be added to these several substances, when they are also to
be rubbed along with quick-lime; but the reason is this. _If the lime
were so quick and fresh as to raise heat when common water is poured
on it, the solution might then be made without the aid of lime water;
but, as it will for the most part happen, that the lime kept in the
shops will not be perfectly fresh, it will be best that the prescriber
should direct lime water to be used._" On the contrary, Dr. Percival
used _lime fresh from the kiln_. These circumstances, if my theory be
just, would greatly vary the event of the experiment; and the trials I
have here recited seem to prove, that so great a quantity of lime, and
even a much smaller than is directed by Dr. Macbride, if fresh, instead
of increasing, diminishes the solvent power of water on astringent

  [u] Percival's Essays Medical and Experimental, 2d Edit. p. 65.

But as different drugs yield their virtues with more ease, and in
greater quantity to some menstrua than to others, it seemed probable,
that even a very small quantity of lime might render water less solvent
of particular vegetables, than it is in its pure state, though with
others as large or perhaps a greater quantity than what I had used
might be necessary: and as the determination of this point might be
of some use in pharmacy, the following experiments were made; in
the relation of which I shall make use of numbers as before, viz.
the vegetable rubbed with four ounces of distilled water will be
distinguished by number 1, that with two scruples of lime and four
ounces of lime water, number 2, and that with lime water only, number


Two drachms of snake root were rubbed for fifteen minutes with the
above-mentioned different proportions of distilled water, quick-lime
and lime water, and lime water alone.

Number 1 was a dark brown tincture, tasting strongly of the serpentaria.

Number 2, straw coloured, taste of the lime disagreeable, that of the
root not distinguishable.

Number 3, amber coloured, tastes of the root.


Two drachms of Columbo being triturated in the same manner,

Number 1, dark brown tincture; tastes much of the Columbo.

Number 2, yellow; faint taste of the Columbo, but that of the lime very
disagreeably prevalent.

Number 3, colour as number 1; but tastes more highly of the Columbo.


Two drachms of contrayerva root with the same treatment yielded in the
following proportions:

Number 1 gave a pale brown tincture, tasting of the contrayerva.

Number 2, bright amber colour; taste of the lime so strong as to admit
of no other.

Number 3 exceeded number 1 both in colour and taste.


Jalap being triturated in the same proportions,

Number 1 dark brown; taste of the jalap strong.

Number 2 pale yellow; taste of the lime predominant, though that of the
jalap perceptible.

Number 3, colour not quite so high as number 1, but equal in taste.


The result of the same trial with ipecacuanha was, that number 1 was
of a light brown colour, tasting highly of the ipecacuanha.

Number 2 was of a deep yellow, having the same disagreeable taste
of the lime complained of in the other tinctures, but that of the
ipecacuanha scarcely perceptible.

Number 3 produced a tincture of the colour of red port wine, strongly
flavoured with the ipecacuanha, though it had not so much of the
distinguishing sharpness of that root as number 1.


The different tinctures of rhubarb, prepared in the same manner as
above, had the following appearances:

Number 1 brown, with a yellowish tinge, strongly impregnated with the
taste of the rhubarb.

Number 2 deep yellow, taste of the lime as in the other tinctures
prepared with it.

Number 3 crimson; taste of the rhubarb strong, but unequal to number 1.

None of the tinctures prepared with lime water grew turbid from a
stream of fixed air being conveyed into them.

Hence it appears that the triture of quick-lime with all the above
roots did not in the least degree promote, but rather impede their
solution in water; that lime water extracts the soluble parts of
many, and especially their colouring principles, more powerfully than
distilled water; but that this is by no means always the case, as in
three instances out of six, the tinctures prepared with distilled water
exceeded those with lime water in taste, and in two instances were
superiour, and in one equal in colour.



Sir John Pringle, in the Appendix to his excellent Observations
on the Diseases of the Army, allows lime water to possess but a
slight antiseptic quality. Doctor Macbride on the contrary asserts,
that it has great power in resisting putrefaction, but at the same
time acknowledges that it destroys the cohesion of the constituent
particles of animal substances, and therefore cannot be called a
_true_ antiseptic, as it absorbs the fixable air from them, and only
preserves them sweet by confining it within their texture, into which
the lime is enabled to insinuate itself in this dissolved state. As
even this effect, if possessed by the tinctures of the antiseptic
vegetables prepared with lime or its water, would be an objection
to their administration in putrid diseases, I resolved to determine
by experiment, how far their antiseptic powers were increased or
diminished by this mode of preparation: and I thought it probable, as
those prepared with the latter contain no lime when filtered, and yet
in the extraction of the tinctures the vegetables are deprived of, at
least, a part of their air, they might be rendered less able to resist
putrefaction than either the infusions prepared with distilled water,
or those with the addition of quick-lime. How far this reasoning was
just, the result will discover.


Pieces of beef, each weighing about two drachms, were separately
infused in the different tinctures of Peruvian bark, snake root,
Columbo, and contrayerva, prepared with lime, lime water, and distilled
water, as in the preceding experiments; and the bottles containing
them were exposed for two days to a degree of heat equal to that of
the human blood. They were afterwards suffered to remain without any
artificial heat, the temperature of the air being warm. The tincture of
Columbo prepared with quick-lime was the only one not tried, the bottle
containing it having been broken.

After thirty-six hours infusion they were all sweet, except the
infusion of Columbo in distilled water, which began to emit a
disagreeable, though not putrid foetor. The beef in it, and in the
tincture of the same root in lime water, was swelled, and whiter than
before infusion. That in the tincture of bark prepared with quick-lime,
had its texture greatly destroyed, was of a chocolate colour, but
sweet. That in aqua calcis, the same in colour, shrivelled, firm,
and sweet. The pieces of beef in the tinctures of snake root and of
contrayerva with quick-lime, had more the appearance of calf's lights
than of beef, were quite spongy, but had acquired no putrid smell.
Those in the lime and distilled water, firm, and shewing no signs of

On the fifth day the infusion of Columbo in lime water was very
offensive, though the beef when taken out of it was not putrid. That of
the same root with distilled water had made no further progress. The
tincture of snake root in distilled water was grown turbid, and had
lost colour, which it seemed to have imparted to the beef. This and all
the others continued sweet.

On the tenth day the beef in the distilled water and Columbo, as on the
fifth. That in the lime water and Columbo, putrid.

The contrayerva infusion in distilled water had acquired a disagreeable
foetor, but the beef was not yet putrid. That with lime water and
that with quick-lime still sweet.

The infusion of bark with distilled water smelled rather musty; the
beef in it sweet. The two infusions of the same with lime and lime
water shewed no further change.

The tincture of snake root in distilled water had a scum on the
surface; beef not putrid. The other two tinctures of the same root

On the eleventh day, the beef in the infusions of Columbo and of
contrayerva in distilled water beginning to putrefy, and

On the fourteenth day, both entirely putrid. The infusion of bark in
distilled water mouldy, but the beef sweet.

The beef in the snake root and distilled water, putrid on the sixteenth
day; and the infusion of contrayerva with lime water beginning to be
offensive, but the beef in it not yet putrid; but

On the nineteenth it was quite putrefied. The snake root infusion in
lime water, mouldy on its surface; no change in the beef; but this
likewise became putrid in a few days more.

The remaining tinctures, viz. those of the bark, snake root, and
contrayerva with quick-lime, and that of the bark with lime water,
remained above five weeks without any further change. Some time
after, the beef in the snake root became septic. The other three were
unaltered at the end of six weeks from their first immersion; and
though the infusion of bark in distilled water was very mouldy, the
beef in it was free from any putrid foetor. But it should be observed
that all the tinctures in the preparation of which quick-lime had been
added to the lime water, had a peculiar odour during the whole time,
from which the others were exempt.

From this experiment we may conclude that lime water, when used in
such a quantity in extracting the virtues of vegetables, as not to
be saturated with the fixed air it receives from them, _strongly_
counteracts putrefaction, though it at the same time destroys the
texture of animal bodies exposed to its action. But when employed for
the same purposes, in such proportion as to be fully saturated with
air; it abstracts nothing from, but rather increases the antiseptic
power of the vegetable; nor does animal flesh immersed in tinctures
thus prepared, suffer any diminution in the cohesion of its fibres.



The very curious fact, that fixed air not only preserves bodies from
becoming septic, but is also possessed of the power of restoring
sweetness to them when actually putrid, seemed to be established by a
number of very accurate experiments adduced in support of the doctrine
by its ingenious author. This has, however, lately been controverted
by a learned writer, who has favoured the public with _an Experimental
Inquiry concerning the causes which have been generally said to produce
putrid diseases_, in which he has recounted several experiments, in
direct contradiction to those of Dr. Macbride. The authorities of both
these gentlemen deserve considerable attention, and it might seem
presumption in me to attempt to decide between them, had I only my own
opinion to adduce; but as the accuracy of the following trials was
witnessed by a Physician, well known for his medical and philosophical
writings, I feel the less diffidence in submitting them to the public.
They were made with a view, only, to my own information, having in one
of the former chapters recommended Magnesia to be taken in the act of
effervescence with an acid, as a corrector and evacuant of putrid bile;
but as the event appeared to be so satisfactory, and as a determination
of this point is the more important, from the late introduction of
fixed air as an article of the materia medica, I hope I shall not be
deemed to have impertinently obtruded into the dispute by relating
them, and endeavouring to point out what, probably, has been the cause
of Dr. Alexander's drawing conclusions, so contrary to those of the
other celebrated experimentalist.

In the experiments which Dr. Alexander has related in support of his
opinion, he has made use of the following methods. He included pieces
of putrid mutton in bladders, one containing _four ounces in measure_
of fixed air from fermenting wort; another the same quantity from wort
with a piece of putrid mutton in it; and the third, only _about half
the quantity_ from a mixture of bread, water, and saliva. In another
experiment, he exposed a slice of beef that had just begun to have the
putrid smell, to a stream of air brought over from an effervescing
mixture of distilled vinegar and salt of wormwood. In a third, the
putrid flesh was suspended in the neck of a wide mouthed bottle,
while _four ounces_ of distilled vinegar were made into _spirit.
minderer._ In a fourth, _four ounces_ of air from bottled small beer
were confined twenty-four hours with the putrid substance, which in
a fifth experiment was put into the neck of a bottle of small beer,
while it fermented before the fire for half an hour. In a sixth, the
septic body was included in a bottle with _eight ounces_ of air from
an effervescing mixture of common vinegar and salt of hartshorn. In
one only, out of all these experiments, he found the beef in any-wise
sweetened, and even in that single instance, though he at first thought
the piece a little changed, yet when washed it recovered its putrid
smell. However he confesses, that by bringing over fixed air from
several other fermenting and effervescing mixtures, on pieces of meat
just beginning to putrefy, they were rendered a little sweeter, though
never to such a degree, as entirely to lose their putrid taint.

So very different an account of so interesting a subject was truly
mortifying: The old adage, _experientia fallax, judicium difficile_,
seemed to be too applicable to the present occasion. Some cases, in
which fixed air used medicinally as an antiseptic, appeared to have
produced good effects, had occurred to some of my medical friends[v],
and I even flattered myself that I had directed it to good purpose
in an instance or two. But if the theory on which this practice was
founded should be false, the whole superstructure seemed likely to be
destroyed. On revising Dr. Alexander's book, I imagined that I had
discovered some thing in the conducting of his experiments, which might
account for their terminating so differently from those of Dr. Macbride.

  [v] See Dr. Percival's Experiments and Observations, p. 72; Dr.
  Priestley's papers on factitious air; and Mr. White's Treatise on the
  Management of Pregnant and Lying-in Women, p. 203.

The largest quantity of fixed air which Dr. Alexander made use of
in any of these experiments was _eight ounces in measure_, and in
one instance, only two ounces were employed to sweeten the putrid
substance. In that where the meat was suspended in a wide mouthed
bottle while the vinegar was made into _spirit. minderer._ no method
seems to have been taken to retard the too rapid flight of the fixed
air, which, from the quick distribution of the salt, would be soon
dissipated. From hence I suspected, that a larger atmosphere, or a
longer continued stream of fixed air might be requisite to restore
septic bodies to perfect sweetness; and in order to decide this point,
the following experiments were instituted, having previously obtained
some slices of beef so exceedingly putrefied as to render the foetor
of them scarcely tolerable.


A bottle capable of containing three pints was filled with water, and
inverted into a bason of the same; a tube which communicated with
another bottle, in which was an effervescing mixture of chalk and oil
of vitriol, was then introduced into the mouth of the former, and a
stream of fixed air continued, till the whole of the water was driven
out by it. A piece of the above-mentioned putrid beef, fastened by a
string to a cork, was conveyed into the bottle, which was corked before
it was taken out of the water. The beef, after having been suspended in
this atmosphere of fixed air for thirteen hours, was very considerably,
though not entirely sweetened. _But the air in the bottle seemed
to have acquired all the putrid smell of which the flesh had been
deprived._ Another slice of the same beef was not at all sweetened by
exposure, during the same time, to the open air.


A piece of this beef suspended all night in the neck of a bottle of
artificial Pyrmont water[w], was rendered less putrid, though not near
so much altered as that in the foregoing experiment. The water was
strongly impregnated with the putrid effluvia.

  [w] See Dr. Priestley's Directions for impregnating Water with fixed


Two drachms of Magnesia Alba diluted with two ounces of water were
placed in a quart bottle, to which was added a sufficient quantity of
the strong spirit of vitriol to let loose all the fixed air from the
Magnesia, during the separation of which, another equally putrid piece
of beef was suspended in the bottle, which was so corked as to retard,
though not totally prevent the escape of the air. Another piece of the
same beef, was exposed in like manner to the vapour arising from the
addition of oil of vitriol to two drachms of chalk diluted with water.
They were suffered to remain for twenty two minutes, and being then
examined were absolutely free from any putrid foetor, and though well
washed in water continued quite sweet.


Air expelled from Magnesia by the nitrous acid, sweetened a piece of
the same putrid flesh suspended in the neck of the bottle during the
effervescence. The beef smelled of the nitrous acid, but remained
equally sweet when washed from it in water. Very little change was
produced in another piece exposed to the smoaking spirit of nitre.

It may be some additional evidence in support of the sweetening
properties of fixed air, to declare that the highly offensive, sanious
discharge of a cancer has been rendered considerably sweeter by it[x];
and that I have seen a case of a dysenteric fever, attended with
extremely foetid and bloody stools, in which fixed air was directed,
by the Physician who attended, to be thrown into the intestinal tube
by way of clyster; the consequences of which were the correction of the
putrid smell of the discharges, and the reduction of the inflation of
the abdomen, together with contributing considerably to the ease of
the patient after each injection of air[y]. A third case of this kind
has very lately occurred to Dr. Percival, in which the injection of
fixed air removed the foetor of the stools, and the patient recovered
without the assistance of any other medicine, except the moderate use
of wine as a cordial, and of a decoction of Peruvian bark during the
convalescent state. I have also experienced the removal of a very
large and deep slough, and the healing of the ulcer in the putrid sore
throat, more expeditiously by the inspiration of fixed air than by any
other method.[z]

  [x] Directions for impregnating Water with Fixed Air, by Joseph
  Priestley, L.L.D. F.R.S.

  [y] This case, together with another similar to it, will probably
  appear more fully in the next volume of the Philosophical Transactions,
  with Dr. Priestley's papers on factitious air.

  [z] The patient in this last case being a lady in the country, at such
  a distance that I could not frequently visit her; by continuing to
  inspire the fixed air, after the ulcer was cleansed, and in a healing
  state, brought on a considerable inflammation of the fauces.

One circumstance in the twenty ninth experiment peculiarly attracted
my attention, viz. that the air in the bottle was so very putrid,
though the beef exposed to it was restored to sweetness. The septic
effluvium therefore did not appear to be destroyed, but to have changed
place. From this fact it occurred to me that there might possibly be
an affinity between the fixed air and the septic particles, and that
this air might act as a menstruum on the effluvia emitted by putrid
bodies. I have since had the pleasure to see that Dr. Priestley, whose
investigation into the nature of factitious air has lately been laid
before the Royal Society, and must contribute to exalt him to a still
higher rank as a Philosopher, has taken notice of something similar
hereto. I am sensible that difficulties attend this theory. Doctor
Percival, in the second volume of his Essays, which is now in the
press, has offered some ingenious conjectures on the subject, and to
them I refer the reader. I shall only mention one experiment which
seems to give some force to this doctrine.


Slips of linen cloth dipped in very rancid oil, had their rancidity
much diminished by exposure to a stream of fixed air from an
effervescent mixture of chalk and spirit of vitriol. But a pint bottle
of the same oil being saturated with this vapour, was equally offensive
as before the air was thrown into it, though the oil appeared to absorb
a considerable quantity of air.

Dr. Macbride exposed a piece of rag dipped in lixivium tartari, and
another tinged blue by the scrapings of raddishes, to the vapour
arising from a large vat of melasses wash in high fermentation, without
any change being effected in either, which could be supposed to
proceed from an acid vapour. But as water impregnated with fixed air
has evidently an acidulous taste, and it seemed probable that some of
the vitriolic acid might be volatilized during the effervescence which
proceeds from its admixture with the alkaline body, when the air is
procured from these substances, it was apprehended that the antiseptic
and sweetening powers of air thus obtained, might depend on the acid
contained in it. In order to evince how far this conjecture was just,
Doctor Percival was so obliging to assist me in suggesting and making
the following experiments.


Twenty drops of syrup of violets mixed with a glass-full of water were
changed into a lively red by the addition of one drop of dilute spirit
of vitriol. The season of the year did not allow us to use the fresh
juices of vegetables, but this trial shews the genuineness of the syrup
of violets, and that it was a sufficiently delicate test of acidity.


A paper besmeared with this syrup, was placed over a vessel which
contained an effervescing mixture of chalk and oil of vitriol. No
change of colour took place except in one small point[aa], which had
probably been accidentally touched by the vitriolic acid.

  [aa] In making this experiment, if the vegetable juice be placed too
  near to the effervescing mixture, some particles of the acid will be
  forced up to it, together with the air, and may occasion an erroneous
  conclusion to be drawn from it.


Twenty drops of the syrup of violets were added to a glass-full of
water strongly impregnated with fixed air, after the method directed
by Dr. Priestley[ab], but without any variation in the colour of the

  [ab] Directions for impregnating water with fixed air, &c. by Joseph
  Priestley, L.L.D.


A few drachms of the syrup of violets were dissolved in half a pint of
water, which was afterwards impregnated with air from an effervescing
mixture of chalk and the smoaking spirit of nitre; but the syrup of
violets suffered no change of colour.


A piece of putrid flesh which had been sweetened by the vapours of iron
filings and the nitrous acid, had a pungent, acidulous smell. It was
carefully washed in water, and still remained free from putridity. A
few drops of lixivium tartari were instilled into this water without
producing any sensible effervescence.

May we not infer from these experiments, that if fixed air be an acid,
it is an extremely weak one, and not sufficient, as such, to sweeten
putrid bodies; which effect must consequently be owing to some other
mode of action, the principles of which are not as as yet positively



1. The due preparation of MAGNESIA ALBA depends on the proper mixture
of the alkaline lixivium with the solution of the sal catharticus
amarus; on the precipitated powder being immediately thrown into a
very large quantity of boiling water; on the purity of the water used
in the process; on the expeditious drying of the medicine, and on an
exact attention to cleanliness.

2. The artificial Epsom salt, or _sal catharticus amarus_, affords
Magnesia, at least, equally pure with that obtained from the Epsom
waters; and as the writers[ac] on mineral waters mention those of Epsom
to contain besides their salt, a considerable quantity of unneutralized
earth, which appears, from Dr. Rutty's experiments, to be calcareous,
they should seem peculiarly unfit for the purpose of preparing
Magnesia. Some of the _Epsom Magnesia_ being calcined, impregnated
distilled water with a calcareous earth.

  [ac] Allen, Lucas, Rutty, Monro, &c.

3. A sufficiently strong and well purified lixivium of potashes is
equally adapted to procure the precipitation of Magnesia, as a ley made
with salt of tartar, or any other fixed alkali.

4. MAGNESIA ALBA differs essentially in its chemical and medicinal
properties from every other known absorbent earth; and when mixed with
an acid, either before or after its admission into the stomach, is
_purgative in a much smaller quantity_ than chalk, crab's eyes, or any
of the calcareous or testaceous earths.

5. The calcination of Magnesia divests it of those disagreeable
properties complained of by Hoffman, and other practitioners; the fixed
air which constitutes so great a share of its composition, and is the
cause of the uneasy sensation produced by this powder, being expelled
in the process. But depriving the Magnesia of its air does not render
it caustic or unfit for internal uses.

6. It is a common, but unchemical practice, to mix acid and alkaline
substances in the same composition, without attending to the changes
which will be produced in their nature by being united. Among other
instances of this kind which might be pointed out, we often meet with
lenitive electuary, cream of tartar and Magnesia Alba prescribed
together in one medicine, the consequence of which is, that the
Magnesia is not only unintentionally neutralized, but the effervescence
produced in it by the acid occasions the electuary to swell and renders
it unsightly, besides altering the nature of the pulps and syrup which
enter the composition, by inducing a vinous fermentation in them. The
calcined Magnesia being a non-effervescent may be united with acids
under this form without any other inconvenience than their producing
a neutral salt, and the propriety of this change must depend on the
intention of the prescriber.

7. It appears that Magnesia Alba, though remarkably septic to animal
flesh, retards the putrefaction of bile, and restores sweetness to it
when actually putrid: That these last effects are still more strongly
produced by the calcined Magnesia, which also powerfully resists the
corruption of flesh: That some of the other absorbents prove antiseptic
to bile; and consequently that the opinion of the universal septic
property of the absorbent class of medicines, and of the impropriety of
prescribing them in bilious diseases, may admit of some exceptions.

8. Magnesia, when calcined, has the same property as quick-lime of
promoting the solution of resinous gums in water.

9. The increased power of water as a menstruum to vegetable
astringents, depends on only such a quantity of lime being employed as
can be saturated with air by the _solvend_; but if a larger proportion
be used, the action of the water on the vegetable is rather prevented
than promoted.

10. Though lime water in several instances appears to be a more
powerful menstruum to vegetables than distilled water; yet the latter
is sometimes preferable, and acts more efficaciously than when
impregnated with lime.

11. Antiseptic vegetables yield tinctures to lime water, which resist
putrefaction more powerfully than those prepared from the same drugs
with distilled water, without lessening the cohesion of animal fibres.

12. Waters which contain a large quantity of calcareous earth, either
simply suspended, or in a neutralized state, are highly improper for
pharmaceutical purposes in general, and especially for the preparation
of extracts, where much water and long continued boiling are requisite.

13. The power of fixed air to restore sweetness to putrid bodies, is,
it is hoped, clearly established: and there appears to be some degree
of probability, that fixed air produces this effect by acting as a
menstruum to the putrid effluvia: It seems also to be proved, that its
antiseptic quality is not owing to any acidity which it carries off
with it from the effervescing mixture.


[Illustration: Decorative Band]

  Experiments and Observations
  Strictures on Mr. GLASS'S MAGNESIA.

  By THOMAS HENRY, Apothecary.

  Manchester, March 8, 1773.

IT is with the utmost reluctance I find myself indispensibly obliged to
address the public on a subject, from the nature of which I may perhaps
incur the suspicion of acting from interested views: should I be so
unhappy, my friends who know me will, I trust, do me the justice to
acquit me of the charge of being influenced by any improper motives;
and I shall hope for the candid indulgence of those persons to whom I
am a stranger.

About a year and half since I transmitted to the College of Physicians
an account of a method of preparing Magnesia Alba, equal to that which
had been long sold by Mr. Glass of Oxford, and which was generally and
deservedly esteemed by others, as well as by myself, to be the standard
of purity. Though that gentleman carefully concealed the minutiæ on
which the success of his process depended, he had always prepared it
with the most laudable attention.

My process was received by the College, and published in the second
volume of the Transactions of that truly respectable society, and has
since been reprinted in a pamphlet which I lately published, and in
which, among other subjects, I have recommended Calcined Magnesia to
the attention of the faculty, as a medicine of considerable importance.

Notwithstanding I had been informed, by a relation of Mr. Glass, that
he had disposed of his name in the Magnesia business to some persons,
for a very valuable consideration, yet I doubted not their adhering to
the proper manner of preparing it; but as I have since had occasion to
change my opinion, and as the credit of the Calcined Magnesia depends
so much on its purity before calcination, I am necessitated to take
this method of informing the public of my reasons for declaring that
sold under the name of Mr. Glass to be impure, calcareous, and improper
for the purpose of calcining.

Two or three years had elapsed since I had seen any of Mr. Glass's
Magnesia, except a small quantity which I had preserved, as a standard
for the levity of what I prepared myself. But having a mind to calcine
some of his, in order to compare it with my own, I sent for a box from
Mr. Harrop, an agent of the proprietors in this town. I was surprized,
on opening if, to find the Magnesia specifically lighter, to an amazing
degree, than any I had formerly seen, insomuch that the six shillings
box, which used to contain about four ounces, now only contained an
ounce and half, Troy weight: _so that this medicine is sold at the rate
of two pounds eight shillings the Troy pound, which is not fourteen
ounces Avoirdupois_. On attempting to dissolve it in the vitriolic
acid, I found the solution very imperfect; and on calcining half of
the contents of the box, it was with indignation that I discovered
this Magnesia, so extolled, so puffed in every newspaper, for _its
superior purity and goodness_, to contain no inconsiderable quantity of
calcareous earth; for the pungency of it was very disagreeable in the
mouth, and one scruple of it impregnated an ounce of water almost as
strongly as so much lime would have done. These are tests, which, tho'
much stronger than that of levity which the proprietors have artfully
placed as the principal one, they have avoided mentioning, being
sensible of its deficient solubility, and that it would not stand the

Willing, however, to believe that this impurity might be accidental,
though I had reason to think, from the artful conduct above alluded
to, that it was not so, I sent for a box of Magnesia, from the agent
for the sale of Mr. Glass's Magnesia at Preston. This likewise proved
calcareous, though I thought the lime, produced by calcining it, not
quite so pungent as the other; it, however, made a strong lime-water.
That I might avoid drawing too hasty conclusions, I procured a third
box from Chester, which being subjected to the same trials, seemed
more impure than either of the other two. This Magnesia formed a very
imperfect solution in the vitriolic acid; and the taste of the lime,
after calcination, was so very disagreeable, that I was not free from
it for some hours. The water impregnated with it was as strong to the
taste as common lime-water, and the precipitate which fell from it,
on blowing air into it, was as copious as I ever observed from that
prepared with stone or oyster-shell lime. The boxes were all purchased
from the agents for the sale of Glass's Magnesia, and every box was
sealed with his arms, and had every other mark of authenticity. I have
retained samples of each in both states.

I have since repeated the above experiments on the contents of two
boxes of Glass's Magnesia, the one of which was purchased of Mr. R.
Davis, in Sackville-street, Piccadilly, the other of Mr. William
Nicoll, in St. Paul's Church-yard. The Magnesia in each proved to be
calcareous, and acquired the properties of quick-lime by calcination.

It would be natural for every person, who might wish to give the
Calcined Magnesia a fair trial, to obtain Mr. Glass's for that purpose,
on the supposition of its being superior to any other; and as the very
first taste of it, in that state, would be sufficient to prejudice any
one against the farther use of it, I am necessitated, in justice to my
own reputation, and to the public, who may otherwise be deprived of a
very valuable medicine, to enter this protest against the use of it.

I have fairly and candidly given up to the public what I have found
to be the best method of preparing Magnesia, sufficiently pure for
every medical and chemical purpose; and I sincerely wish that every
apothecary, who has opportunity and leisure, would prepare it himself.
But as, from various reasons, there are, I am convinced, too many who
omit to do it, and that too little attention is paid to examining
into the purity of what is used; and as it also appears the public
have been imposed on, where they had reason to think themselves most
secure, I have sent to Mr. JOHNSON, No. 72, St. Paul's Church-yard,
and Mr. RIDLEY in St. James's-street, a quantity of Magnesia, both in
a calcined and uncalcined state, which, though not EQUAL IN LEVITY,
nor quite so costly, even when calcined, as that sold as Mr. Glass's,
will, I doubt not, prove to be non-calcareous, and superior to it in
every other respect. And if it should appear so to the gentlemen of the
faculty, I wish for no preference to those apothecaries who prepare the
medicine faithfully; but flatter myself that I have a superior title to
the favour of physicians, of my brethren, and of the community, than
those persons can claim, who have meanly stooped to secrete a process,
the knowledge of which must be beneficial to mankind, and have abused
the public confidence.

I shall only add, that so far was I from expecting to find Mr. Glass's
Magnesia impure, that I bought it as a standard; that, as I am informed
that Gentleman is dead since this inquiry was finished, nothing, less
than the reasons I have adduced, could have prevailed on me to have
published this Appendix at this season; and that I do not consider
him, but the present preparers of the Medicine, as culpable for the
adulteration. That I have been favoured with an account of some
experiments made by a Physician of considerable eminence, on that
Magnesia, the result of which was similar to what I have here recited;
and I appeal for proof of the truth of what I have asserted, to every
reputable person who may now have any of it in his possession, and will
make the experiment; and that having rested my cause on that issue, I
mean not to enter into any controversy on the subject.

N. B. Calcareous Magnesia is neither so absorbent, nor so purgative as
the pure.


       *       *       *       *       *

  Transcriber's Notes

  Obvious typographical errors have been corrected, but variations in
  spelling, punctuation and hyphenation have been retained. In
  particular, the phrase "head achs" in Chapter III. has been retained.

  Experiment I was erroneously numbered II. This has been corrected.

  Footnote identifiers are italic in the book. The italic markers have
  been omitted for the sake of clarity.

  The reference to AN APPENDIX has been added to the Table of Contents.

  The Errata listed have been corrected in the text.

  Italics are shown thus _italic_.

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