Consequently, in the former instance, 16 parts of magnesia were contained in 800,000 parts of water, or 1 of the earth in 50,000 of the fluid; whilst in the latter, the respective proportions were as 1 to 24,000.

The same insensibility to the presence of magnesia, I find to be possessed by the phosphate of ammonia, which Dr Murray has proposed to substitute for phosphate of soda *; but I am not aware that this test, which is somewhat less easily procured, possesses any positive advantages over the latter, except where we wish to analyse the residual liquor after the separation of the magnesia, as in the examination of a mineral water.

In such cases, it is better no doubt to employ a salt having a base of ammonia, which, in all its combinations, admits of being readily disengaged, than to make use of a fixed salt, where the alkali might by its presence occasion some perplexity in our subsequent operations.

In order to ascertain the comparative accuracy of these two tests, I made use of given quantities of sulphate of magnesia, a salt, the composition of which, in its crystallised state, appears to be pretty accurately determined.

From 50 gr. of this substance dissolved in water, I obtained, by means of phosphate of soda, a triple salt, which, when dried under an exhausted receiver, in connection with recently fused muriate of lime, amounted to 45.8 gr., and was reduced by a red heat to 20.3; whilst, from the same quantity of sulphate of magnesia, treated with phosphate of ammonia, I obtained 44.5 gr. of triple phosphate, which, after exposure to the same temperature with the former precipitate, weighed 19.7.

But as it is difficult, by the method employed above, to deprive the ammoniacó-magnesian phosphate of the whole of its water †, and as a very inconsiderable heat decomposes

See Dr Murray's "General Formula for the Analysis of Mineral Waters," in the Edinburgh Philosophical Transactions.

+ Unless this be admitted, we must suppose a larger quantity of ammonia to enter into the composition of the triple phosphate than Dr Marcet imagines, ac

it*, I prefer calculating the quantity of magnesia from the residuum, after exposure to a red heat, taking it in both instances at 40 per cent. of the precipitate.

The analysis, therefore, by phosphate of soda, indicates 20.3 gr. of phosphate of magnesia, equivalent to 8.1 of the pure earth; that by phosphate of ammonia 19.7 gr., or 7.88 of base. Now, we have stated, on the authority of the latest experiments, that 50 gr. of crystallised sulphate of magnesia contain 8.0 of base, which is nearly the mean between the two analyses.

To satisfy myself still further that the whole of the magnesia is thrown down by this re-agent, I observed whether potash, which (as I shall afterwards mention) is one of the most delicate tests of magnesia, produced any effect on a magnesian solution, after the alkaline phosphate had ceased to act; but although this re-agent was added in considerable quantity to water that had contained solutions both of sulphate and muriate of magnesia, the liquor remained, in either case, just as transparent as before.

(To be concluded in next Number.)

cording to the calculation made by him of the proportion between the amount of the base present in the precipitate, before and after exposure to a red heat. For, as he estimates the former at 19, and the latter at 40 per cent. of the whole, the precipitate by phosphate of soda ought, in that case, to have been reduced from 45.8 gr. only to 21.75; and the one obtained by phosphate of ammonia from 44.5 to 21.14. For, as 40: 19::45.8: 21.75; and as 45.8 : 21.75 :: 44.5: 21.14. Whereas the residuum in the former was less by 1.45, and in the latter by 1.44. The circumstance that the two precipitates were reduced by a red heat, in exactly the same ratio, (corresponding to theth of a grain), whilst it gives me some confidence in the accuracy of the results themselves, seems rather to favour the idea that the quantity of ammonia present exceeds Dr Marcet's statement, for it is not likely that the precipitates, after remaining under an exhausted receiver, should have both retained precisely the same proportion of water. I am unwilling, however, to call in question the experiments of so accurate a chemist, without having more solid grounds to go upon.

100

* I have found that the triple phosphate begins to be decomposed at a temperature very little exceeding 100° of Fahrenheit.

ART. XIX.-Researches on Hydrocyanic Acid and Opium, with reference to their Counter-Poisons. By JOHN MURRAY, Esq. F. L. S. M. W. S. &c. Communicated by the Author.

IN June 1815, a paper of mine was read to the Linnean Society, developing a simple and apparently decisive method of ascertaining the sedative virtues of vegetable juices and their counter-agents.

The sciatic nerves of the prepared frog were taken up by a silver probe, and moistened with the tincture, and the result indicated the sedative power or its obverse; the degree was determined by the specific gravity of the solution employed, and the power measured by the duration of the period required to produce its maximum effect.

It would be superfluous now to describe what has already been amply detailed. It was clearly proved from the result, that a suspension of the voltaic excitement, more or less decided, was the consequence of certain vegetable juices, and that in such as were operative in this manner, acetic acid was found to be a counteragent.

It may be worthy of remark in this place, that discoveries have since manifested new alkaline bases, characterised by specific characters in such as having produced a sedative effect, were neutralised by acetic acid, as morphia, atropia, &c.

The following paper is intended simply to detail the results of some experiments, instituted with reference to the discovery of counter-poisons to their agency on the system. Facts are soon detailed; and it is not necessary that they be amplified or extended by unnecessary details. The truths gleaned from actual experiment are immutable, while the consequences which may be deduced in support of a theory, may soon be overlooked in the progression of intelligence.

I had always found, that the violent headach which sometimes occurred in preparing hydrocyanic or prussic acid, was relieved and removed by ammonia, which induced me to think that the antidote to that acid, and virulent and formidable poison, might be found in ammonia.

A small portion of hydrocyanic acid was given to a healthy young rabbit, which proved fatal in ten minutes. Soon after its administration, the head declined on one side, violent spasm supervened, while the eye lost its lustre, and the animal died in dreadful convulsions.

On dissection after death, the lobes of the lungs appeared paler than usual, coagulable lymph was found lining the tra chea, as in Cynanche Trachealis, and the stomach was found inflamed near the pylorus. The brain was not examined.

The muscular fibre was still excitable by voltaic agency, but the excitability soon declined.

A drop or two of hydrocyanic acid on the head of a frog soon proved fatal. The colour promptly changed to an unwonted paleness.

The sciatic nerves of the prepared limbs were moistened with hydrocyanic acid, but no suspension of the voltaic excitement supervened. It was accompanied by a tremulous movement of the muscular fibre, connected with the lines of the nerves; and this spontaneous irritability seemed increased by the application of alcoholic solution of iodine.

It is a singular fact, that not unfrequently an alcoholic solution of iodine, dropped on the muscular fibre of a frog, excited phenomena similar to the action of the voltaic apparatus. It seemcd also to renew excitability when the susceptibility had declined or was lost.

When the symptoms were verging to a fatal issue in a frog, a drop or two of ammonia on the head effectually restored the animal.

A greater quantity of hydrocyanic acid was given to a young rabbit than proved fatal in the case detailed. Ammonia was occasionally applied to the mouth on a sponge. The animal exhi bited no unhealthy symptom whatever.

A considerable quantity of the hydrocyanate of ammonia with excess of base, was administered to another rabbit, but without any deleterious effect.

Half a drachm of hydrocyanic acid was given to a healthy young rabbit. The effects were prompt. Respiration became laborious and difficult, with a grating in the throat,—the eye lost its brilliancy,-the head dropped,-it raised a sharp cry, and

was convulsed. Strong ammonia was dropt into the animal's mouth, and it was repeatedly moistened with a sponge dipped into ammonia. It almost instantly revived, and even licked repeatedly the finger which sometimes applied the ammonia, apparently quite sensible of the instant and continued relief it afforded. The animal effectually recovered. Its lips were excoriated by the ammonia.

Conscious of the complete antidote to this formidable poison found in ammonia, I took a quantity of hydrocyanic acid, sufficient to produce violent headach, stupefaction, &c., but diluted ammonia afforded me instant relief. I occasionally applied it to the olfactory organs, and bathed the forehead.

Since hydrocyanic acid has been introduced into our pharmacopoeia, and employed in phthisis pulmonalis, and accidental poisoning may be anticipated, it is of much moment to know an ef fectual barrier to its virulence; and such is my complete conviction of the antidote, that I would feel no hesitation whatever in taking a quantity sufficient to prove fatal, provided there stood 'by a skilful hand to administer the remedy.

It is admitted that morphia is the active principle in opium. Morphia dissolved in alcohol, in which, however, it is sparingly soluble, produced, on the sciatic nerves of a prepared frog, effects analogous to those of the tincture of opium. Acetic acid restored the voltaic excitability.

The sciatic nerves were moistened with superacetate of morphia, but the excitement was the same as if none had been applied. A frog's head and abdominal viscera were steeped in superacetate of morphia, but the voltaic action remained unchanged.

Half a drachm of superacetate of morphia was given to a young rabbit, but no apparent derangement of its healthy functions took place it rather seemed to act as a stimulus to appetite.

These experiments pointed out acetic acid as the counter-poison to opium, and from its volatile properties, and other charac ters, in which it differs almost essentially from acetous acid, having no affinity with it except in an acid character, and having much of the features of an ether, I am of opinion acetic acid may prove serviceable where acetous acid would not prove effectual. Two and a half drachms of tincture of opium were given to a rabbit. In a short time the eye became more opake, the pupil