An account of the medicinal virtues of magnesia alba: more particularly of calcined magnesia; ... By Thomas Henry, ...

AN ACCOUNT OF THE MEDICINAL VIRTUES OF MAGNESIA ALBA, &c.

ABOUT two years since I published a small volume of Experiments and Observations on va∣rious Subjects, which also contained some ac∣count of the diseases in which Magnesia Alba is particu∣larly useful, and a recommendation of that medicine in a state of calcination, as preferable, in many instances, to the uncalcined Magnesia. But as the remarks on this subject are intermixed with a number of others which are only interesting to medical or philosophical readers, I have been frequently requested to draw up a plain detail of the history and medicinal uses of Magnesia, for the use of those persons who may be purchasers of the medi∣cine, and to whom the other part of my former publica∣tion would be entirely useless.

Previous therefore to the recital of the virtues of Mag∣nesia, it may not be improper to give a short history of the invention of this medicine, and of the gradual pro∣gress by which it has arrived at the degree of estimation in which it now stands.

To those mineral bodies which contain metallic earths, the earlier Chemists gave the name of Marcasites; and those earths, which were capable of attracting the acid from the atmosphere, and thereby forming salts, were termed Magnesia. The first preparers of Magnesia Alba, who procured it from the mother-ley of nitre, or liquor remaining after the crystallization of that salt, imagining it to be the proper absorbent of the nitrous acid, are supposed to have given it the name of Magnesia, and the epithet Alba appears to have been added as a distinction, on account of its superior whiteness.

Magnesia Alba was first introduced by the Jesuits at Rome, and the preparation of it was concealed by them, for some time, as a nostrum. But the secret, at length, was divulged, and its use became more general in several countries on the continent. It has been observed above that it was at first prepared from the mother-ley of nitre, and it was sometimes obtained by evaporating the liquor, and afterwards driving off, by means of a strong fire, the acid with which it was combined; and sometimes by precipitating the Magnesia by pouring in a sufficient quantity of an alkaline lixivium.

The powder, thus prepared, was not however pure Magnesia. A quantity of wood ashes and quick-lime are necessary to the crystallization of nitre, and, in con∣sequence, the Magnesia, separated from the liquor re∣maining

maining after that process, contained a proportion of these substances. Besides, as but little nitre is prepared in Europe, the difficulty of obtaining the liquor in suffi∣cient quantity was an impediment to the general prepa∣ration of Magnesia. That excellent Physician and inge∣nious Chemist, Hoffman,* 1.1 was induced, from the simi∣larity between that lixivium and the brine remaining af∣ter the crystallization of sea salt, to try whether Magne∣sia might not be precipitated from the latter. The ex∣periment succeeded to his wishes, and he even found the powder, thus obtained, to be more purgative than the other. His animadversions and experiments on this preparation were published, and engaged the attention of physicians to a medicine so strongly recommended by that celebrated professor. Dr. Black, to whom we are obliged for many ingenious experiments tending to in∣vestigate the Chemical History of Magnesia, rendered the process still more easy by substituting the bitter purg∣ing salt, commonly known by the name of Epsom Salt, which is prepared from the last mentioned brine, instead of the brine itself, thereby enabling chemists to prepare the medicine, though at a distance from those places where sea-water is evaporated.

The process, notwithstanding, published by Dr. Black, was little known, and in some respects defective. Mag∣nesia Alba was indeed sold in the shops, but ill prepared, coarse and adulterated. Scarcely any was to be met with, in a tolerable state of purity, except what was prepared by the late Mr. Glass of Oxford, who, having

bestowed much attention on the subject, produced it greatly superior to any at that time vended. This gentleman however had not the generosity to divulge his process, but carefully concealed it as a profitable nostrum.

About sixteen years ago, I happened to reside in the neighbourhood of Mr. Glass; I had before that time frequently prepared Magnesia, but had never been able to make it equally fine as his, though far superior to what was commonly sold. My ambition was excited, I wished to attain to a like degree of perfection, and, after many trials I arrived at the desired point, and found, by repeated comparisons, that the Magnesia which I pre∣pared, equalled that of Mr. Glass in every respect.

When I left Oxford, I made no other use of the dis∣covery I had made than preparing Magnesia for my own shop, and freely communicating what I knew on the subject to my acquaintance. After some years it occur∣red to me that it might be of public utility to draw up an account of the method I had made use of, and to de∣liver it to the College of Physicians, who are the proper guardians of medicine in this kingdom. I accordingly transmitted my process to the College, who did me the honour of publishing it in their Transactions.* 1.2

Some time after the publication of the Volume of Transactions which contained my method of preparing Magnesia; Dr. Saunders, a very ingenious physician in London, whose extensive knowledge in chemistry has been displayed in several publications, mentioned in con∣versation, to Dr. Percival, the great improvement which

Magnesia was capable of receiving by calcination. That by this means it might be deprived of those disagreeable qualities which occasioned flatulencies in the bowels of some tender people, and had brought the medicine into a degree of disrepute. My worthy friend, sensible how much I was interested in every discovery on that subject, communicated the information to me, and on trial of this process, I found the Magnesia improved to the ut∣most of my expectation; it was perfectly mild, and as free from causticity after as before calcination; it operated in half the dose, and occasioned none of those disagree∣able sensations in the bowels which often follow the use of common Magnesia.

From hence I was insensibly led into a train of other experiments which have been since published,* 1.3 and it is hoped may have contributed to explain the nature of Mag∣nesia, and determine its medicinal properties more accu∣rately than had hitherto been done. In the course of these experiments, it was observed that the Calcined Magnesia did not dissolve so rapidly in the vitriolic acid as the uncalcined, and being desirous of comparing some other with my own, and imagining I might depend on the purity of that vended under the name of Mr. Glass, who had, some time before, sold his process to Mr. Delamotte, who then resided, as a stationer, at Weymouth; I purchased a box, from the agent for the sale of it in Manchester, that I might calcine it, and observe whether it acquired the same or different properties from that which I had prepared.

The result of these experiments, and the caution with which I proceeded, has been already delivered to the public; and the torrent of abuse, which has so plentifully flowed upon me in consequence of the disco∣very, is notorious. Conscious of my own integrity, I have stood undaunted at the attacks which malice and revenge suggested. The unchemical doctrines, the ab∣surd inferences, the glaring contradictions, and illiberal language, with which the publications of my antago∣nists abounded, served only to convince the public of the badness of a cause so meanly, so ungenerously de∣fended.

Notes

• * 1.1

  Hoffman, Vol. 4. p. 500.
• * 1.2

  Vide Medical Transactions, Vol. 2. p. 226.
• * 1.3

  Experiments and Observations on various Subjects, by Thomas Henry, London, 1773.