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    EXPERIMENTS

    AND

    OBSERVATIONS

    ON THE

    FOLLOWING SUBJECTS;

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

    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
    putrefaction.

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

    6. On the Sweetening Properties of FIXED AIR.

    BY

    THOMAS HENRY, APOTHECARY.

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

    SYDENHAM.


    LONDON:

    Printed for JOSEPH JOHNSON, No. 72,

    St. Paul's Church-Yard.

    MDCCLXXIII.




  TO

  THOMAS PERCIVAL, M.D.
  F.R.S. & S.A.

  DEAR SIR,

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,


  DEAR SIR,

  Your truly affectionate

  and very humble Servant,

  THOMAS HENRY.

  MANCHESTER,
  18th Jan. 1773.




THE

PREFACE.


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.




THE

CONTENTS.

  CHAP. I.                         Page

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

  CHAP. II.

  _Miscellaneous Observations._      12

  CHAP. III.

  _On the Medicinal Properties of
  Magnesia Alba._                    25

  CHAP. IV.

  _On the Calcination of Magnesia
  Alba._                             39

  CHAP. V.

  _On the Medicinal Virtues of
  Calcined Magnesia._                48

  CHAP. VI.

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

  CHAP. VII.

  _On the Solvent Qualities of Calcined
  Magnesia._                         80

  CHAP. VIII.

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

  CHAP. IX.

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

  CHAP. X.

  _On the Sweetening Properties of
  Fixed Air._                       114

  CHAP. XI.

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

  AN APPENDIX                       143




ERRATA.

  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_.




CHAP. I.

AN ACCOUNT OF AN IMPROVED METHOD OF PREPARING MAGNESIA ALBA.


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
_pharmacopaeia_ 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
successful.

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.




CHAP. II.

MISCELLANEOUS OBSERVATIONS.


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