A REVIEW OF THE GENERAL CONCLUSIONS DEDUCIBLE FROM THE FOREGOING
OBSERVATIONS AND EXPERIMENTS.
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.
_THE END._
[Illustration: Decorative Band]
AN
APPENDIX
TO
Experiments and Observations
On the PREPARATION of
MAGNESIA, &c.
CONTAINING
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
FIERY ORDEAL.
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.