Part 5
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 violets.
[ab] Directions for impregnating water with fixed air, &c. by Joseph Priestley, L.L.D.
EXPERIMENT XXXVII.
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.
EXPERIMENT XXXVIII.
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 defined?
CHAP. XI.
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._
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.
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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_.