has shown, by numerous experiments, that it produces two very important effects. 1. It increases the rapidity of the combustion. 2. It greatly increases the quantity of gaseous matter evolved. Upon these two circumstances the force of gunpowder entirely depends. Proust has shown that the quantity of sulphur ought not to exceed 12.5 grains, supposing the nitre to amount to 75 grains, otherwise the rapidity of the combustion is dimi nished. Charcoal having a much greater affinity for oxygen than sulphur, the combustion of the gunpowder ought, theoretically speaking, to depend upon the charcoal. There can be little doubt, that it is the charcoal chiefly which burns; though probably the sulphur likewise comes in for a share. It is obvious, that the charcoal can serve no purpose whatever in the powder, except as far as it is consumed. Now 76 parts of nitre contain about 38 parts of nitric acid. The quantity of oxygen in this acid has not been ascertained in an unexceptionable manner; but, by the highest calculation, it cannot amount to more than five times the azote present; and there is reason to believe that it does not fall far short of that quantity. Hence it is probable, that the oxygen present in 76 parts of nitre amounts to 30 parts. We are certain that it cannot exceed that quantity. Now 15 parts of charcoal require for combustion no less than 37.5 parts of oxygen. The quantity of charcoal which would consume 80 parts of oxygen would be 12 parts. From these considerations, it follows, that the best proportions of the constituents of gunpowder would be the following:

Nitre...

Charcoal

Sulphur.

76

12

12

100

Or, perhaps, the sulphur might be diminished to ten parts, without impropriety. For it appears from Proust's experiments, that such a proportion of sulphur would produce its full effect. The advantage of these new proportions would be a stronger powder, or at least as strong a powder, two per cent. lighter than the powder at present in use.

VI. Test of Alumina.

Mr. J. Gotlieb Gahn, the celebrated discoverer of the metallic nature of manganese, and of the composition of the earth of bones, has pointed out a valuable test for discovering the presence of alumina in mineral substances exposed to the action of the blow-pipe. It is as follows. Place upon the substance to be tried a drop of nitrate of cobalt, and expose it to the white flame of the blow-pipe. If the mineral contain alumina in any quantity, and is not too much charged with iron, or other

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colouring metals, it soon acquires a blue colour, more or less brilliant, and more or less intense; according to the purity and the abundance of the alumina which it contains. "I had never," says M. Gahn, in a letter to the editor of this journal," extended the application of this experiment to minerals of a very great degree of hardness, such as the sapphire, the spinell, corundum, topaze, &c.; but the other day I was under a kind of necessity of making the trial, and I observed, with pleasure, that all these substances exhibited the blue colour as well as others. It is only necessary to pulverize them well, and expose them to the action of the blow-pipe in the manner above described. This test labours under one disadvantage, however ; for the earth of zircon produces the same blue colour with cobalt as alumina does."

VII. Extracts from two Letters of Dr. John Redman Coxe, Professor of Chemistry in Philadelphia.

1. "It has long been unknown upon what principle the combustion of pyrophyrus depended. Mr. Davy, since his discovery of potassium, has ascribed it to its presence in some way. A few weeks past I had occasion to lecture on this substance (pyrophyrus); and finding a portion, which I had prepared some time before (but which had failed, except in one or two instances), to be useless, I was under the necessity of making some fresh. After the first portions of gas had escaped, and the inflammable gas began to come over, I was, near the period I intended to stop the process, struck with the appearance of the flame, which possessed, as I thought, the rose-coloured flame of potassium. I immediately stopt the process; and obtained as fine pyrophyrus as I ever met with. Reasoning upon the subject, I was led to suppose that the frequent failure of the process depended on our carrying it so far, that the potassium formed was entirely consumed. In consequence of this, I poured out all my old pyrophyrus, and found that no combustion ensued. To this mass I added 30 or 40 drops of a pure alkaline solution potash), and exposed it, as usual, to heat, in a crucible surrounded with sand. Inflammable gas began to escape, and at length appeared tinged with a rose-coloured flame; when I stopt the process, and when cool poured the contents into a dry warm vial. This possessed, in a very excellent degree, the properties of perfect pyrophyrus. I apprehend, in this compound, the potassium is diffused through the mass in its metallic state, and, eizing on the atmospheric moisture, gives origin to some potassuretted hydrogen, which, inflaming by the contact of : oxygen, communicates combustion to the carbonaceous materials surrounding it. If it existed in any other form than metallic, ought it to be so long, as we sometimes see it, before

combustion ensues? and why should moisture be necessary often, as by breathing on it? In this preparation, either not carrying on the heat sufficiently long to metallize the potash, or, beyond this, to its complete burning off, will equally prejudice it. If my idea was correct, as to the colour of the flame, we may have a criterion to judge when to stop."

2. "In places where Welter's tubes of safety cannot be had, such an arrangement of Woulfe's apparatus as will enable an operator to saturate water with the gases, without danger from absorption, cannot fail of being acceptable. The following plan explains such a method, which supersedes the use of Welter's tubes, and will permit the absence of the operator, without danger from absorption.

"The tube E is twice bent at right angles, with legs of equal length; one descends to the bottom of the tubulated receiver, A; the other to the bottom of a three-necked bottle, B. In this bottle is placed the only tube of safety, F, which is necessary, descending about half an inch below the surface of the

water.

"The tube G is twice bent, and only perforates the corks, without descending into the bottles B and C.

"The tube H, bent as before, descends to the bottom of the bottles C and D. Other bottles may be added at pleasure, connected as C and D; that is, having the tubes near the bottom of each bottle; or, perhaps, rather as represented above.

"If the apparatus is wanted to saturate water with muriatic acid gas, a little water must be put in B, as usual, to absorb any sulphurous acid gas evolved; C is left empty; and into D, &c. must be introduced the distilled water to be saturated.

"If during the absence, or from inattention of the operator, an absorption should take place, the water in B will pass up the tube E, and be deposited on the bottom of the empty receiver. When the orifice of the tube F is exposed, the air will rush into the bottle B ; and by its presence, if the absorption is great, will force the remaining water into the receiver, until the orifice of the tube E is exposed, when the air will pass through the tube E, and, rising through the water in the receiver, restore the equilibrium.

"A part of the water in bottle D will rise simultaneously with the solution in B, and pass into C; but as the tube G does not

descend to the bottom, it can pass no farther, and is preserved from contamination by the sulphurous gas in the bottle B. Further, after the orifice of tube F is exposed, the atmospheric air, rushing in through G, arrests the further passage of the liquid of D.

"When an absorption has thus taken place, by exciting a fresh action in the retort, the gas accumulates in the receiver; and when sufficient to support a column of fluid of the height of one leg of the tube E, the fluid in the receiver will be forced into the bottle B again; when the gas will follow and pass into C; when, acting on the surface of the liquid that may have come over into it, it forces it back through H into D, and the process of saturation will proceed as before.

"If a bent funnel is used, as I, the equilibrium is still sooner restored, by the air passing through it at once into the retort.

"In obtaining nitric acid, when the strong acid is desired to be kept unmixed in the receiver, it will be advisable to place an empty bottle between the receiver and bottle B; connecting it and the receiver as B and C; and connecting B with it, as B is above connected with the receiver.

"Since writing the above I have tried the apparatus, I think very fairly; and find it answer all I could wish. Where, however, the extrication of gas is very sudden, and large in amount, it will be best to leave each alternate bottle empty. Thus:

"The Gentleman who has improved this apparatus, as described above, has, within a few days, suggested the plan of a self-registering contrivance to send over the acid which may be required in the retort for the decomposition of the materials. This I mean to try in a few days. The plan is simply thus: From the tubular of the retort

goes a bent tube into a bottle of (say) sulphuric acid to the bottom. When absorption of the extricated gas, from the materials in the retort, takes place, the atmos

pheric pressure will force some acid up the

&c.

ribe, and it will pass into the retort; and this will occur as

often as the acid is so far neutralised as to be unable to keep up an adequate action. You will comprehend the intention by this rough sketch-for which I beg you to pardon me, as I am unexpectedly engaged, and must finish this for the packet about to sail."

ARTICLE XI.

Proceedings of Philosophical Societies.

ROYAL SOCIETY.

THE Royal Society, as usual, resumed its sittings on Thursday the 5th of November. The Right Hon. Sir Joseph Banks, Bart. in the chair. A letter from Sir Humphrey Davy to the President was read, giving some account of a new and very extraordinary detonating compound. This is the combination of chlorine and azote, of which we have given some account in the preceding article. Our information on the subject was chiefly derived from Sir Humphrey Davy's letter. We shall only add here the method of preparing the compound. Expose a weak solution of nitrate of ammonia to chloric gas in a jar ; the gas absorbed, and after a certain time a yellow oily-looking substance is seen floating on the surface of the solution. This is the substance in question. Great caution is requisite in making experiments on it. Oxalate of ammonia, and several other ammoniacal salts, were tried instead of nitrate, and were found to answer the purpose.

is

On the 12th of November, a paper by the Astronomer Royal, Mr. Pond, was read, on the summer solstice and the mural quadrant at Greenwich.

On the 19th, a paper on near sight, and the best remedies for defective vision, by Mr. Ware, was read. There is reason to believe, from the observations of Mr. Ware, that this disease is much promoted by the use of glasses; and that if glasses are not employed, it soon wears off and disappears. Hence it is much more common among the higher ranks than among the common people. In the regiments of Life Guards Mr. Ware did not find a single person afflicted with the disease, and not above five or six recruits had been dismissed on account of defective vision; while in one of the colleges at Oxford, consisting of 125 students, no less than 37 were near sighted.

On the 26th, the Bakerian lecture was read by Dr. William Hyde Wollaston, on the constitution of those crystalline bodies whose primitive form is the octahedron or tetrahedron. It is well known to crystallographers, that a kind of anomaly exists with respect to these bodies, as far as regards their primitive form. When an octahedron is subjected to mechanical division, it is separated into octahedrons and tetrahedrons. The same holds