Part 1

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 quæ 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 _pharmacopæia_ 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 crystallize, and easily melts when exposed to the air: with distilled vinegar, a saline uncrystallizable mass is formed, resembling glue both in colour and consistence while warm, but becoming brittle when cold. Dr. Black says, that two drachms of this salt purged a middle aged man four times; and half an ounce of the same gave a woman of a strong constitution no less than ten stools.[e]

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

[e] Ibid. p. 64.

Besides, where an acid prevails, much smaller doses than two drachms of Magnesia prove purgative; and it seldom happens that even that dose of the other absorbents[f] will produce the same effect. Nor am I singular in my opinion, when I declare my doubt whether Magnesia be not of itself in some degree purgative, independent of its junction with any acid whatsoever. It appears to be an earth _sui generis_. That of alum resembles it in some respects, yet differs from it essentially, when combined with the vitriolic acid: the alum is strongly astringent and antiseptic, the Epsom salt purgative and septic.

[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.

I have very lately seen a paper signed by Doctor Cadogan and dated in the year 1767, in which he complains grievously of the advertisers of Magnesia, making use of his name without his consent, and has published the process for making _his_ Magnesia. The doctor's intent in this was doubtless benevolent, but his manner of preparing this powder is unnecessarily expensive and wasteful. He directs only one pound of lixivium tartari to five pounds of sal catharticus amarus, which is greatly insufficient to precipitate all the Magnesia. And he insists strongly on the superiority of the lixivium prepared from salt of tartar, to that made of potashes, as if the chemical effects of one, were different from the other. But, says the Doctor, potashes render the Magnesia bitter. Surely the vitriolated tartar produced by a union of one vegetable fixed alkali with the vitriolic acid, is equally soluble in water with that prepared with any other, and if so, will be as easily washed off from the Magnesia.

But behold a champion steps forth, and at one blow levels to the ground the whole tribe of Magnesia makers, who have procured it from the factitious Epsom salts. I confess I have not had the happiness to peruse this ingenious gentleman's pamphlet on the subject, but I have formed a very extraordinary opinion of his _candour_, _modesty_, _and knowledge_, from the very curious paper which he distributes with his Magnesia. Notwithstanding Doctor Black, and since him Mr. Glass and several others, have procured _pure_ Magnesia from the factitious Epsom salts, Mr. Dale Ingram, assures us, that he has made an improvement, "which is by the learned esteemed one of the greatest acquisitions to the materia medica." And wherein does this mighty discovery consist? even that Magnesia prepared from the waters of Epsom, is superiour to that prepared from the bitter purging salt; and he assures us that the Magnesia sold by him is so prepared.

To the first assertion I shall only reply, that every person at all conversant in chemistry knows that Magnesia earth is the same, from whatever substance it can be separated in a pure state; that the factitious Epsom salt yields it in as great a degree of purity as the salt of the Epsom water, and that Dr. Alston assures us, the artificial salt "by various and repeated experiments, made in France as well as in Britain, is demonstrated to be every way as good as, yea to be the very same with, the genuine made of the Epsom waters."[g]

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

As to the other declaration, it will be sufficient to observe that one gallon of Epsom water contains only seven drachms of salt in a dry season, and hardly six drachms in a wet one;[h] and that for this salt to precipitate its Magnesia properly, it is necessary it should be diluted with little more than its own weight of water.[i] Six drachms of salt will yield two drachms of Magnesia. So that to procure a pound of this powder Mr. Ingram must evaporate above sixty gallons of the water, to between five and six pints, before he begins the precipitation. Sure never did empiricism appear so thinly disguised!

[h] Ibid.

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

In the preceding chapter, the necessity of using water free from any calcareous impregnation has been particularly insisted on, and I have, on another occasion,[j] observed that great attention should be given to the purity of the water used in the making of all the saline preparations; and I may add in almost all the operations of pharmacy. Dr. Percival, in his ingenious experiments on water, found a quart of the Manchester pump water to contain upwards of sixty grains of adventitious matter.[k] Suppose therefore, for instance, that in making the extract from a pound of peruvian bark, it be boiled only six times in the quantity of water directed by the London Dispensatory, nine gallons will be consumed in the process; which is a very moderate allowance, six coctions not being sufficient to extract all the virtues of that drug. Dr. Percival boiled half an ounce of bark twenty five times, in so many different pints of water, the last of which had some impregnation, and the residuum gave a deep colour, and considerable bitterness to rectified spirit of wine. If we likewise suppose only one half of the foreign contents of such water to be left by evaporation, then the quantity of calcareous and saline matter, undesignedly mixed with the extract, will be two ounces and two drachms, or nearly equal to the quantity of extract procured from a pound of bark by pure water. Thus this important medicine becomes grossly adulterated, without any such intention in the operator; and I know it is the common practice to use pump water in making it.

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

[k] Ibid. p. 87.

I have particularly selected the Peruvian bark, as requiring a very large quantity of water to extract the whole which it is capable of yielding; but the proportion of water which I have here allowed, will not be too great in obtaining extracts from most vegetable substances; and how greatly not only the quantity, but the quality of the medicine must be affected by the admixture of such a weight of insoluble calcareous earth, is so obvious, that it is needless to expatiate on it.

CHAP. III.

ON THE MEDICINAL PROPERTIES OF MAGNESIA ALBA.