On the solvent qualities of CALCINED MAGNESIA.
DR. Macbride, whose experimental researches have very justly acquired him a high degree of reputation in the philosophical world, supposes fixed air to be the combining principle of bodies, and has applied this ingenious theory to pharmaceutical improvements. He discovered that lime triturated with resinous gums,promotes their dissolution in water; which, he thinks, is thus enabled to take up the same parts of these substances, as are soluble in spirit of wine. These aqueous tinctures are transparent, not milky like the solutions made with yolk of egg, or gum arabic; but the lime communicates a highly disagreeable taste to them, and the action of lime water, which he used in some instances, is not sufficiently powerful to extract strong tinctures from these bodies. As calcined Magnesia has a great affinity with fixed air, I was desirous of trying whether it would contribute to render resinous substances soluble in water; for being itself insoluble, the solutions would consequently be free from any other impregnation than that of the resins.
EXPERIMENT X.
Five grains of camphor were rubbed for five minutes with an equal quantity of calcined Magnesia: after the camphor was reduced to powder, it united into a hard concrete with the Magnesia, but immediately dissolved on the addition of a small quantity of distilled water, of which an ounce was mixed with them, and immediately passed through filtering paper. The filtrated liquor was highly impregnated with the camphor.
EXPERIMENT XI.
Five grains of opium triturated in the same manner, yielded atransparent tincture, of as deep a colour as the tinctura Thebaica of the London Dispensatory, and tasting strongly of the opium.
EXPERIMENT XII.
Gum guaiacum and calcined Magnesia, of each a scruple, being rubbed with an ounce of water, and filtered, gave an elegant green tincture, quite transparent, and possessing, in a considerable degree, the taste of the gum.
Gum galbanum, storax, mastick, myrrh, assafætida, scammony and balsam of Tolu, being severally triturated with equal weights of calcined Magnesia, diluted with water and filtered, afforded neat tinctures, strongly impregnated with the different drugs.
EXPERIMENT XIII.
In order to determine the quantity of opium thus dissolved, half an ounce of crude opium, the same quantity of calcined Magnesia, and eight ounces of distilled water were rubbed for a quarter of an hour in a glass mortar, and having stood to infuse during two hours, the liquor was separated through paper. The tincture was of a darker colour than that before described, and was reduced by a gentle heat to a pilular consistence. This extract weighed sixty-eight grains, which, allowing for impurities, for what would be dissipated in evaporation, and for the air probably absorbed by the Magnesia, is a large proportionto be so soon dissolved. The residuum which was left in the filter was dried, and weighed six drachms.
EXPERIMENT XIV.
A drachm of Peruvian bark, twenty grains of calcined Magnesia, and four ounces of distilled water being rubbed together during fifteen minutes, the filtered infusion resembled in appearance the simple tincture of bark, and had an intensely bitter taste, but was not strongly impregnated with the peculiar aroma of the bark.
Thus then we have an easy and very elegant method of preparing aqueous tinctures from the gum resins, and administering them in a more convenient form and inlarger doses than could be done when dissolved in a spirituous menstruum; and much more agreeably than in the half-dissolved state to which they are reduced by the aid of egg or gum arabic. The Magnesia does not impart any thing to them, whereas the lime will seldom be so saturated with air but that some part of it will remain soluble in the water: and as they may be given diluted to whatever degree the prescriber chuses, considerable advantages may be expected therefrom, it being probable that they will be better enabled to pervade the very small vessels; and the heating properties of the balsams be more effectually obviated than by any other mode of preparation.
Indeed, tinctures prepared by the above method, are not calculated for officinal compositions, but for extemporaneous prescription; as most of them, except camphor, deposite a sediment when they have been kept a week or two.
On the various solvent powers of QUICK-LIME in different quantities.
THE difficulty of solution in the vegetable astringents has been complained of by various writers on theMateria Medica. Water and alcohol are the menstrua in use; but great quantities of each are necessary to procure even a slight impregnation, and much heat and long boiling are said actually to destroy the astringent quality, and vegetable texture.[t]As a menstruum capable of dissolving them with greater facility appeared to be a desideratum, not only in pharmacy, but in other arts, particularly in that of dying blacks, I resolved to try Dr. Macbride's method of increasing the solvent power of water, by means of quick-lime. But as I was aware that the quantity of lime he made use of in obtaining an aqueous tincture of Peruvian bark, would be too great for the dyer's use, I wished to use only such a quantity as would be sufficiently saturated with the air contained in the vegetable, to be itself precipitated; and to compare the tinctures thus made,with a standard prepared with simple water.
EXPERIMENT XV.
I rubbed three drachms of Aleppo galls reduced to powder, with four ounces of filtered rain water, for fifteen minutes, and then passed the solution through paper. It was very styptic to the taste, and was nearly of the same colour as Huxham's tincture of bark. The residuum in the filter was unchanged in colour. The bottle containing the liquor was marked number 1.
EXPERIMENT XVI.
Three drachms of the samegalls, and two scruples of quick-lime, were triturated with four ounces of rain water, as in the last experiment. The filtered liquor had scarcely any astringency to the taste, and was of a very pale colour. The residuum was of a deep purple. Marked number 2.
EXPERIMENT XVII.
The same quantity of galls as in the two former experiments, after triture in the same degree with four ounces of lime-water, was separated by filtering through paper. The tincture thus obtained was highly astringent to the palate, of a deep chocolate colour, and the residuum was of a lighterbrown than number 1. Marked number 3.
EXPERIMENT XVIII.
To each of the above tinctures were added forty drops of a strong solution of sal martis. Number 1 became very black. Number 2 changed colour but little, and on standing precipitated a brown sediment, which, the superiour part of the liquor being decanted off, became again transparent on the addition of a few drops of the vitriolic acid. Number 3 appeared to strike a deeper black than number 1; and these being tried as inks, number 3 seemed to have the superiority; but a slip of linen cloth being macerated in each forsome hours, that in number 1 had taken a more perfect black than the slip number 3. No trial was made with cotton or woollen, which it is probable would have differed from the linen.
EXPERIMENT XIX.
Oak bark was used instead of galls, with similar success, except that the infusion made with lime-water was not so deep in colour as that with simple rain water, though much deeper than that prepared with quick-lime.
EXPERIMENT XX.
Peruvian bark, quick-lime, andlime water, in the same proportion as directed by Dr. Macbride, were rubbed together. The filtered infusion had little colour, tasted very slightly of the bark, though strongly of the lime, and on my blowing in a stream of air from my lungs, the surface of it was immediately covered with a cremor calcis, the liquor grew turbid, and deposited a copious sediment.
EXPERIMENT XXI.
The same quantity of Peruvian bark, and of lime water, without the addition of any fresh lime, being rubbed in the same manner, afforded a tincture tasting strongly of the bark, nearly of the samecolour as the simple tincture obtained by proof spirit, and retaining its transparency when blown into. This tincture was much more strongly impregnated than one made by triture with common rain water only. And by this process, allowing a few hours for maceration, an infusion is prepared, greatly superiour in strength to any decoction, infusion, or tincture of bark I ever saw.
From the result of these experiments I suspect, that by using a greater quantity of lime in the sixteenth and twentieth experiments than the vegetable could saturate with fixed air, the water became so impregnated with lime as to be more unfit to act on the vegetable. From the purple colour of the residuum of number 2, it was evident that the galls weredecompounded, but the water was not capable of dissolving and suspending the particles. Dr. Percival[u]mentions his having unsuccessfully repeated Dr. Macbride's experiment with bark and quick-lime. To what then can this difference be owing? Perhaps it may be accounted for thus: It seems probable that the lime used by Dr. Macbride, not being fresh calcined, had recovered part of its air; for he says, "It will no doubt be reckoned superfluous, that lime water is ordered to be added to these several substances, when they are also to be rubbed along with quick-lime; but the reason is this.If the lime were so quick and fresh as to raise heatwhen common water is poured on it, the solution might then be made without the aid of lime water; but, as it will for the most part happen, that the lime kept in the shops will not be perfectly fresh, it will be best that the prescriber should direct lime water to be used." On the contrary, Dr. Percival usedlime fresh from the kiln. These circumstances, if my theory be just, would greatly vary the event of the experiment; and the trials I have here recited seem to prove, that so great a quantity of lime, and even a much smaller than is directed by Dr. Macbride, if fresh, instead of increasing, diminishes the solvent power of water on astringent vegetables.
But as different drugs yield their virtues with more ease, and in greater quantity to some menstrua than to others, it seemed probable, that even a very small quantity of lime might render water less solvent of particular vegetables, than it is in its pure state, though with others as large or perhaps a greater quantity than what I had used might be necessary: and as the determination of this point might be of some use in pharmacy, the following experiments were made; in the relation of which I shall make use of numbers as before, viz. the vegetable rubbed with four ounces of distilled water will be distinguished by number 1, that with two scruples of lime and four ounces of lime water, number 2, and that with lime water only, number 3.
EXPERIMENT XXII.
Two drachms of snake root were rubbed for fifteen minutes with the above-mentioned different proportions of distilled water, quick-lime and lime water, and lime water alone.
Number 1 was a dark brown tincture, tasting strongly of the serpentaria.
Number 2, straw coloured, taste of the lime disagreeable, that of the root not distinguishable.
Number 3, amber coloured, tastes of the root.
EXPERIMENT XXIII.
Two drachms of Columbo being triturated in the same manner,
Number 1, dark brown tincture; tastes much of the Columbo.
Number 2, yellow; faint taste of the Columbo, but that of the lime very disagreeably prevalent.
Number 3, colour as number 1; but tastes more highly of the Columbo.
EXPERIMENT XXIV.
Two drachms of contrayerva root with the same treatment yielded in the following proportions:
Number 1 gave a pale brown tincture, tasting of the contrayerva.
Number 2, bright amber colour; taste of the lime so strong as to admit of no other.
Number 3 exceeded number 1 both in colour and taste.
EXPERIMENT XXV.
Jalap being triturated in the same proportions,
Number 1 dark brown; taste of the jalap strong.
Number 2 pale yellow; taste of the lime predominant, though that of the jalap perceptible.
Number 3, colour not quite so high as number 1, but equal in taste.
EXPERIMENT XXVI.
The result of the same trial with ipecacuanha was, that number 1 was of a light brown colour, tasting highly of the ipecacuanha.
Number 2 was of a deep yellow, having the same disagreeable taste of the lime complained of in the other tinctures, but that of the ipecacuanha scarcely perceptible.
Number 3 produced a tincture of the colour of red port wine, strongly flavoured with the ipecacuanha, though it had not so much of the distinguishing sharpness of that root as number 1.
EXPERIMENT XXVII.
The different tinctures of rhubarb, prepared in the same manner as above, had the following appearances:
Number 1 brown, with a yellowish tinge, strongly impregnated with the taste of the rhubarb.
Number 2 deep yellow, taste of the lime as in the other tinctures prepared with it.
Number 3 crimson; taste of the rhubarb strong, but unequal to number 1.
None of the tinctures prepared with lime water grew turbid from a stream of fixed air being conveyed into them.
Hence it appears that the triture of quick-lime with all the above roots did not in the least degree promote, but rather impede their solution in water; that lime water extracts the soluble parts of many, and especially their colouring principles, more powerfully than distilled water; but that this is by no means always the case, as in three instances out of six, the tinctures prepared with distilled water exceeded those with lime water in taste, and in two instances were superiour, and in one equal in colour.
On the Comparative ANTISEPTIC POWERS of vegetable infusions prepared with LIME, &c.
SIR John Pringle, in the Appendix to his excellent Observations on the Diseases of the Army, allows lime water to possess but a slight antiseptic quality. Doctor Macbride on the contrary asserts, that it has great power in resisting putrefaction, but at the same time acknowledges that it destroys the cohesion of the constituent particles of animal substances, and therefore cannot be called atrueantiseptic, as it absorbs the fixable air from them, and only preserves them sweet by confining it within their texture, into which the lime is enabled to insinuate itself in this dissolved state. As even this effect, if possessed by the tinctures of the antiseptic vegetables prepared with lime or its water, would be an objection to their administration in putrid diseases, I resolved to determine by experiment, how far their antiseptic powers were increased or diminished by this mode of preparation: and I thought it probable, as those prepared with the latter contain no lime when filtered, and yet in the extraction of the tinctures the vegetables are deprived of, at least, a part of theirair, they might be rendered less able to resist putrefaction than either the infusions prepared with distilled water, or those with the addition of quick-lime. How far this reasoning was just, the result will discover.
EXPERIMENT XXVIII.
Pieces of beef, each weighing about two drachms, were separately infused in the different tinctures of Peruvian bark, snake root, Columbo, and contrayerva, prepared with lime, lime water, and distilled water, as in the preceding experiments; and the bottles containing them were exposed for two days to a degree of heat equal to that of the human blood. They were afterwards suffered toremain without any artificial heat, the temperature of the air being warm. The tincture of Columbo prepared with quick-lime was the only one not tried, the bottle containing it having been broken.
After thirty-six hours infusion they were all sweet, except the infusion of Columbo in distilled water, which began to emit a disagreeable, though not putrid fœtor. The beef in it, and in the tincture of the same root in lime water, was swelled, and whiter than before infusion. That in the tincture of bark prepared with quick-lime, had its texture greatly destroyed, was of a chocolate colour, but sweet. That in aqua calcis, the same in colour, shrivelled, firm, and sweet. The pieces of beef in the tinctures of snake root and of contrayervawith quick-lime, had more the appearance of calf's lights than of beef, were quite spongy, but had acquired no putrid smell. Those in the lime and distilled water, firm, and shewing no signs of putrescency.
On the fifth day the infusion of Columbo in lime water was very offensive, though the beef when taken out of it was not putrid. That of the same root with distilled water had made no further progress. The tincture of snake root in distilled water was grown turbid, and had lost colour, which it seemed to have imparted to the beef. This and all the others continued sweet.
On the tenth day the beef in the distilled water and Columbo, as on the fifth. That in the lime water and Columbo, putrid.
The contrayerva infusion in distilled water had acquired a disagreeable fœtor, but the beef was not yet putrid. That with lime water and that with quick-lime still sweet.
The infusion of bark with distilled water smelled rather musty; the beef in it sweet. The two infusions of the same with lime and lime water shewed no further change.
The tincture of snake root in distilled water had a scum on the surface; beef not putrid. The other two tinctures of the same root unchanged.
On the eleventh day, the beef in the infusions of Columbo and of contrayerva in distilled water beginning to putrefy, and
On the fourteenth day, both entirely putrid. The infusionof bark in distilled water mouldy, but the beef sweet.
The beef in the snake root and distilled water, putrid on the sixteenth day; and the infusion of contrayerva with lime water beginning to be offensive, but the beef in it not yet putrid; but
On the nineteenth it was quite putrefied. The snake root infusion in lime water, mouldy on its surface; no change in the beef; but this likewise became putrid in a few days more.
The remaining tinctures, viz. those of the bark, snake root, and contrayerva with quick-lime, and that of the bark with lime water, remained above five weeks without any further change. Some time after, the beef in the snake root became septic. The other three were unaltered at the endof six weeks from their first immersion; and though the infusion of bark in distilled water was very mouldy, the beef in it was free from any putrid fœtor. But it should be observed that all the tinctures in the preparation of which quick-lime had been added to the lime water, had a peculiar odour during the whole time, from which the others were exempt.
From this experiment we may conclude that lime water, when used in such a quantity in extracting the virtues of vegetables, as not to be saturated with the fixed air it receives from them,stronglycounteracts putrefaction, though it at the same time destroys the texture of animal bodies exposed to its action. But when employed for the same purposes, in suchproportion as to be fully saturated with air; it abstracts nothing from, but rather increases the antiseptic power of the vegetable; nor does animal flesh immersed in tinctures thus prepared, suffer any diminution in the cohesion of its fibres.
On the SWEETENING PROPERTIES of FIXED AIR.
THE very curious fact, that fixed air not only preserves bodies from becoming septic, but is also possessed of the power of restoring sweetness to them when actually putrid, seemed to be established by a number of very accurate experiments adduced in support of the doctrine by its ingenious author. This has, however, lately been controverted by a learned writer, who has favoured the public withan Experimental Inquiry concerning the causes which have been generally said to produce putrid diseases, in which he has recounted several experiments, in direct contradiction to those of Dr. Macbride. The authorities of both these gentlemen deserve considerable attention, and it might seem presumption in me to attempt to decide between them, had I only my own opinion to adduce; but as the accuracy of the following trials was witnessed by a Physician, well known for his medical and philosophical writings, I feel the less diffidence in submitting them to the public. They were made with a view, only, to my own information, having in one of the former chapters recommended Magnesia to be taken in the act of effervescence with an acid, as a corrector and evacuant of putrid bile; but as the event appeared to be so satisfactory, and as a determination of this point is the more important, from the late introduction of fixed air as an article of the materia medica, I hope I shall not be deemed to have impertinently obtruded into the dispute by relating them, and endeavouring to point out what, probably, has been the cause of Dr. Alexander's drawing conclusions, so contrary to those of the other celebrated experimentalist.
In the experiments which Dr. Alexander has related in support of his opinion, he has made use of the following methods. He included pieces of putrid muttonin bladders, one containingfour ounces in measureof fixed air from fermenting wort; another the same quantity from wort with a piece of putrid mutton in it; and the third, onlyabout half the quantityfrom a mixture of bread, water, and saliva. In another experiment, he exposed a slice of beef that had just begun to have the putrid smell, to a stream of air brought over from an effervescing mixture of distilled vinegar and salt of wormwood. In a third, the putrid flesh was suspended in the neck of a wide mouthed bottle, whilefour ouncesof distilled vinegar were made intospirit. minderer.In a fourth,four ouncesof air from bottled small beer were confined twenty-four hours with the putrid substance, which in a fifth experiment was put into theneck of a bottle of small beer, while it fermented before the fire for half an hour. In a sixth, the septic body was included in a bottle witheight ouncesof air from an effervescing mixture of common vinegar and salt of hartshorn. In one only, out of all these experiments, he found the beef in any-wise sweetened, and even in that single instance, though he at first thought the piece a little changed, yet when washed it recovered its putrid smell. However he confesses, that by bringing over fixed air from several other fermenting and effervescing mixtures, on pieces of meat just beginning to putrefy, they were rendered a little sweeter, though never to such a degree, as entirely to lose their putrid taint.
So very different an account of so interesting a subject was truly mortifying: The old adage,experientia fallax, judicium difficile, seemed to be too applicable to the present occasion. Some cases, in which fixed air used medicinally as an antiseptic, appeared to have produced good effects, had occurred to some of my medical friends[v], and I even flattered myself that I had directed it to good purpose in an instance or two. But if the theory on which this practice was founded should be false, the whole superstructure seemed likely to be destroyed. On revising Dr. Alexander's book, I imagined that I had discovered some thing in the conducting of his experiments, which might account for their terminating so differently from those of Dr. Macbride.
The largest quantity of fixed air which Dr. Alexander made use of in any of these experiments waseight ounces in measure, and in one instance, only two ounces were employed to sweeten the putrid substance. In that where the meat was suspended in a wide mouthed bottle while the vinegar was made intospirit. minderer.no method seems to have been taken to retard the too rapid flight of the fixed air, which, from the quick distribution of the salt, would be soon dissipated. From hence I suspected, that a larger atmosphere, or a longer continued streamof fixed air might be requisite to restore septic bodies to perfect sweetness; and in order to decide this point, the following experiments were instituted, having previously obtained some slices of beef so exceedingly putrefied as to render the fœtor of them scarcely tolerable.
EXPERIMENT XXIX.
A bottle capable of containing three pints was filled with water, and inverted into a bason of the same; a tube which communicated with another bottle, in which was an effervescing mixture of chalk and oil of vitriol, was then introduced into the mouth of the former, and a stream offixed air continued, till the whole of the water was driven out by it. A piece of the above-mentioned putrid beef, fastened by a string to a cork, was conveyed into the bottle, which was corked before it was taken out of the water. The beef, after having been suspended in this atmosphere of fixed air for thirteen hours, was very considerably, though not entirely sweetened.But the air in the bottle seemed to have acquired all the putrid smell of which the flesh had been deprived.Another slice of the same beef was not at all sweetened by exposure, during the same time, to the open air.
EXPERIMENT XXX.
A piece of this beef suspendedall night in the neck of a bottle of artificial Pyrmont water[w], was rendered less putrid, though not near so much altered as that in the foregoing experiment. The water was strongly impregnated with the putrid effluvia.
EXPERIMENT XXXI.
Two drachms of Magnesia Alba diluted with two ounces of water were placed in a quart bottle, to which was added a sufficient quantity of the strong spirit of vitriol to let loose all the fixed air from the Magnesia, during the separation of which, another equally putrid piece of beef was suspended in the bottle, which was so corked as to retard, though not totally prevent the escape of the air. Another piece of the same beef, was exposed in like manner to the vapour arising from the addition of oil of vitriol to two drachms of chalk diluted with water. They were suffered to remain for twenty two minutes, and being then examined were absolutely free from any putrid fœtor, and though well washed in water continued quite sweet.
EXPERIMENT XXXII.
Air expelled from Magnesia by the nitrous acid, sweetened a piece of the same putrid flesh suspendedin the neck of the bottle during the effervescence. The beef smelled of the nitrous acid, but remained equally sweet when washed from it in water. Very little change was produced in another piece exposed to the smoaking spirit of nitre.
It may be some additional evidence in support of the sweetening properties of fixed air, to declare that the highly offensive, sanious discharge of a cancer has been rendered considerably sweeter by it[x]; and that I have seen a case of a dysenteric fever, attended with extremely fœtid and bloody stools, in which fixed air was directed, by the Physician who attended, to be thrown into the intestinal tube by way of clyster; the consequences of which were the correction of the putrid smell of the discharges, and the reduction of the inflation of the abdomen, together with contributing considerably to the ease of the patient after each injection of air[y]. A third case of this kind has very lately occurred to Dr. Percival, in which the injection of fixed air removed the fœtor of the stools, and the patient recovered without the assistance of any other medicine, except the moderate use of wine as a cordial, and of a decoction of Peruvian bark during the convalescent state. I have also experienced the removal of avery large and deep slough, and the healing of the ulcer in the putrid sore throat, more expeditiously by the inspiration of fixed air than by any other method.[z]
One circumstance in the twenty ninth experiment peculiarly attracted my attention, viz. that the air in the bottle was so very putrid, though the beef exposed to it was restored to sweetness. The septic effluvium therefore did not appear to be destroyed, but to have changed place. From this fact it occurred to me that there might possibly be an affinity between the fixed air and the septic particles, and that this airmight act as a menstruum on the effluvia emitted by putrid bodies. I have since had the pleasure to see that Dr. Priestley, whose investigation into the nature of factitious air has lately been laid before the Royal Society, and must contribute to exalt him to a still higher rank as a Philosopher, has taken notice of something similar hereto. I am sensible that difficulties attend this theory. Doctor Percival, in the second volume of his Essays, which is now in the press, has offered some ingenious conjectures on the subject, and to them I refer the reader. I shall only mention one experiment which seems to give some force to this doctrine.
EXPERIMENT XXXIII.
Slips of linen cloth dipped in very rancid oil, had their rancidity much diminished by exposure to a stream of fixed air from an effervescent mixture of chalk and spirit of vitriol. But a pint bottle of the same oil being saturated with this vapour, was equally offensive as before the air was thrown into it, though the oil appeared to absorb a considerable quantity of air.
Dr. Macbride exposed a piece of rag dipped in lixivium tartari, and another tinged blue by the scrapings of raddishes, to the vapour arising from a large vat of melasses wash in high fermentation, without any change being effected in either, which could be supposed to proceed from an acid vapour. But as water impregnated with fixed air has evidently an acidulous taste, and it seemed probable that some of the vitriolic acid might be volatilized during the effervescence which proceeds from its admixture with the alkaline body, when the air is procured from these substances, it was apprehended that the antiseptic and sweetening powers of air thus obtained, might depend on the acid contained in it. In order to evince how far this conjecture was just, Doctor Percival was so obliging to assist me in suggesting and making the following experiments.
EXPERIMENT XXXIV.
Twenty drops of syrup of violets mixed with a glass-full of water were changed into a lively red by the addition of one drop of dilute spirit of vitriol. The season of the year did not allow us to use the fresh juices of vegetables, but this trial shews the genuineness of the syrup of violets, and that it was a sufficiently delicate test of acidity.
EXPERIMENT XXXV.
A paper besmeared with this syrup, was placed over a vessel which contained an effervescing mixture of chalk and oil of vitriol. No change of colour took place except in one small point[aa], which had probably been accidentally touched by the vitriolic acid.
EXPERIMENT XXXVI.
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.
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 lixiviumtartari 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?
A review of the GENERAL CONCLUSIONS deducible from the foregoing observations and experiments.
1.THE due preparation ofMagnesia Albadepends on the proper mixture of the alkaline lixivium with the solution of the sal catharticus amarus; on the precipitated powder being immediately thrown into avery 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, orsal 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 theEpsom Magnesiabeing calcined, impregnateddistilled water with a calcareous earth.
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 Albadiffers 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, ispurgative in a much smaller quantitythan chalk, crab's eyes, or any of the calcareous or testaceous earths.
5. The calcination of Magnesia divests it of those disagreeableproperties 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, theconsequence 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 thesolvend; 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.
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TOExperiments and ObservationsOn thePreparationofMAGNESIA, &c.CONTAININGStrictures on Mr.Glass's Magnesia.ByThomas Henry, Apothecary.
Manchester, March 8, 1773.