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a a. Cerebellum.

bb. Two of the tubercula quadrigemina.

cc. The part which corresponds with the fourth ventricle in the human brain, surrounded by an oval, continued, nervous band, from which the principal nerves go off.

ddd. Portions of the three semicircular canals of the ear in the cartilaginous cavity in which they are contained.

PLATE XXI.

A view of the upper surface of the brain of the Squalus Acanthias, taken from a fish three feet long, to shew the difference of appearance and size between it and that of the Squalus Maximus.

The brain is entire, and the eyes are left in their situation, so that when this Plate is compared with that of the large brain, the parts that are wanting in it will be readily distinguished.

PLATE XXII.

A view of the heart of the Lophius Piscatorius in a distended state, shewing the transparency of its coats, which are extremely thin.

a. The auricle.

b. The ventricle.

c. The branchial artery.

d. The projecting muscular tube serving as a valve.

XXVIII. Some further Observations on a new detonating Substance. In a Letter from Sir Humphry Davy, LL.D. F. R. S. V. P. R. I. to the Right Hon. Sir Joseph Banks, Bart. K. B. P.R.S.

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MY DEAR SIR,

Read July 1, 1813.

Berkeley square, June 20, 1813.

HAVE already described, in a letter which you were so good as to communicate to the Royal Society, a few facts respecting a new detonating compound. I shall now do myself the honour of inentioning to you some other particulars on the subject.

I received, in April, a duplicate of the letter in which the discovery was announced, containing an Appendix, in which the method of preparing it was described. M. AMPERE, my correspondent, states that the author obtained it by passing a mixture of azote and chlorine through aqueous solutions of sulphate, or muriate of ammonia. It is obvious, from this statement, that the substance discovered in France, is the same as that which occasioned my accident. The azote cannot be necessary; for the result is obtained by the exposure of pure chlorine to any common ammoniacal salt.

Since I recovered the use of my eyes, I have made many experiments on this compound; it is probable that most of them have been made before in France; but as no accounts of the investigations of M. DULONG on the substance have

appeared in any of the foreign journals which have reached this country, and as some difference of opinion and doubts exist respecting its composition, I conceive a few details on its properties and nature will not be entirely devoid of interest.

I have been able to determine its specific gravity, I hope, with tolerable precision, by comparing its weight at 61° FAHRENHEIT, with that of an equal volume of water. 8,6 grains. of the compound, carefully freed from the saline solution in which it was produced, filled a space equal to that filled by 5,2 grains of water, consequently its specific gravity is 1,653.

When the compound is cooled artificially, either in water or in solution of nitrate of ammonia, the fluid surrounding it congeals at a temperature a little below 40° FAHRENHEIT, which seems to be owing to its becoming a solution of chlorine; for, as I have stated in a paper published in the Philosophical Transactions, the saturated solution of chlorine in water freezes very readily. The congelation of the fluid, in contact with the new compound, led me, when I first operated on it in very small quantities, to suppose it readily rendered solid by cooling; but I find in experimenting upon it, out of the contact of water, that it is not frozen by exposure to a mixture of ice and muriate of lime.

The compound gradually disappears in water, producing azote, and the water becomes acid, and has the taste and smell of a weak solution of nitro-muriatic acid.

The compound, when introduced into concentrated solution of muriatic acid, quickly resolves itself into gas, producing much more than its own weight of elastic fluid, which proves to be pure chlorine, and the solution evaporated affords muriate of ammonia.

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In concentrated nitric acid it afforded azote.

In diluted sulphuric acid it yielded a mixture of azote and oxygen,

It detonated in strong solutions of ammonia. In weak solutions it produced azote.

It united to or dissolved in sulphurane, phosphorane, and alcohol of sulphur, without any violence of action, and dissolved in moderately strong solution of fluoric acid, giving it the power of acting upon silver.

When it was exposed to pure mercury, out of the contact of water, a white powder and azote were the results.

The first attempt that I made to determine the composition of the detonating substance, after my accident, was by raising it in vapour in exhausted vessels, and then decomposing it by heat; but in experiments of this kind, even though the whole of the substance was expanded into elastic matter, yet the vessel was often broken by the explosion, and in several instances violent detonations occurred during the process of exhaustion, probably from the contact of the vapour of the substance with the oil used in the pump.

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In the only instance in which I was able to examine the products of the explosion of the substance in an exhausted vessel, no muriatic acid or water was formed, and chlorine and azote were produced; but it was impossible to form any correct opinion concerning the proportions of the gaseous matter evolved, as an unknown quantity of common air must have remained mixed with the vapour in the vessel.

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The action of mercury on the compound appeared to offer a more correct and less dangerous mode of attempting its analysis; but on introducing two grains under a glass tube

filled with mercury and inverted, a violent detonation occurred, by which I was slightly wounded in the head and hands, and should have been severely wounded, had not my eyes and face been defended by a plate of glass attached to a proper cap, a precaution very necessary in all investigations of this body.

In using smaller quantities and recently distilled mercury, I obtained the results of the experiments, without any violence of action; and though it is probable that some accidental circumstance might have occasioned the explosion of the two grains, yet I thought it prudent, in my subsequent experiments, to employ quantities which, in case of detonation, would be insufficient to do any serious mischief.

In the most accurate experiment that I made, ths of a grain of the compound produced, by its action upon mercury, 49 grain measures of azote. I collected the white powder which had been formed in this and other operations of the same kind, and exposed it to heat. It sublimed unaltered, without giving off any elastic or fluid matter, which there is the greatest reason to believe would not have happened, if the compound had contained hydrogen, or oxygen, or both. The sublimed substance had the properties of a mixture of corrosive sublimate and calomel.

If the results of this experiment be calculated upon, it must be concluded that the compound consists of 57 of azote to 643 of chlorine in weight, or 19 to 81 in volume; but this quantity of azote is probably less than the true proportion, as there must have been some loss from evaporation, during the time the compound was transferred, and it is possible that a minute quantity of it may have adhered to mercury not immediately within the tube.

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