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.

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.

FINIS.

FOOTNOTES:

[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.

[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.

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

[e] Ibid. p. 64.

[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.

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

[h] Ibid.

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

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

[k] Ibid. p. 87.

[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 Œconomia NaturÆ, p. 56.

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

[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.

[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.

[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 experiment.

[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.

[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.

[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 ingredients.

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

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

[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.

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

[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.

[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.

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

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

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.

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

The Errata listed have been corrected in the text.

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