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structure as a strong confirmation of it. If we compare the structure of muscles in the human body, with that of the membranous bag, a structure evidently endowed with a similar principle of action, the theories of muscular motion, which are founded on the anatomical structure of a complex muscle, must be overturned. The simplicity of form, in the muscular structure of this species of hydatid, makes it evident that the complex organisation of other muscles is not essential to their contraction and relaxation, but superadded for other purposes; which naturally leads us to suppose that this power of action, in living animal matter, is more simple, and more extensively diffused through the different parts of the body, than has been in general imagined.

On the Nature of the Diamond. By SMITHSON TENNANT, Esq. F.R.S.-[1797.]

As the nature of the diamond is so extremely singular, it seemed deserving of examination; and it will appear from the following experiments, that it consists entirely of charcoal, differing from the usual state of that substance only by its crystallised form. From the extreme hardness of the diamond, a stronger degree of heat is required to inflame it, when exposed merely to air, than can easily be applied in close vessels, except by means of a strong burning lens ; but with nitre its combustion may be effected in a moderate heat.

To expose it to the action of heated nitre free from extraneous matters, I procured a tube of gold, which by having one end closed might serve the purpose of a retort, a glass tube being adapted to the open end for collecting the air produced. To be certain that the gold vessel was perfectly closed, and that it did not contain any unperceived impurities which could occasion the production of fixed air, some nitre was heated in it till it had become alkaline, and afterwards dissolved out by water; but the solution was perfectly free from fixed air, as it did not effect the transparency of lime-water. When the diamond was destroyed in the gold vessel by nitre, the substance which remained precipitated lime from limewater, and with acids afforded nitrous and fixed air; and it appeared solely to consist of nitre partly decomposed, and of aerated alkali.

The quantity of fixed air produced by the diamond does not differ much from that which, according to M. Lavoisier, might be obtained from an equal weight of charcoal. In the Memoirs of the French Academy, he has related the various

experiments which he made to ascertain the proportion of charcoal and oxygen in fixed air. From those which he considered as most accurate, he concluded that 100 parts of fixed air contain nearly 28 parts of charcoal and 72 of oxygen. He estimates the weight of a cubic inch of fixed air under the pressure and in the temperature above mentioned, to be .695 parts of a grain. If we reduce the French weights and measures to English, and then compute how much fixed air, according to this proportion, 24 grains of charcoal would produce, we shall find that it ought to occupy very nearly the bulk of 10 ounces of water.

Experiments to determine the Force of fired Gunpowder. By BENJ. Count RUMFORD, F. R. S. M.R.I.A.— [1797.]

MR. ROBINS, who made a great number of very curious experiments on gunpowder, concluded, as the result of all his enquiries and computations, that the force of the elastic fluid, generated in the combustion of gunpowder, is 1000 times greater than the mean pressure of the atmosphere. But Daniel Bernouilli determines its force to be not less than 10,000 times that pressure, or 10 times greater than Mr. Robins made it. In a paper printed in the year 1781, I gave an account of an experiment, by which it appeared that, calculating even on Mr. Robins's own principles, the force of gunpowder, instead of being 1000 times, must at least be 1308 times greater than the mean pressure of the atmosphere.

In order to make this experiment, I caused a new barrel to be constructed for that purpose: its length was 3.45 inches, and the diameter of its bore of an inch: its ends were closed up by two screws, each one inch in length, which were firmly and immovably fixed in their places by solder. The result of this experiment fully answered my expectations. The generated elastic fluid was so completely confined that no part of it could make its escape. The report of the explosion was so very feeble as hardly to be audible: indeed, it did not by any means deserve the name of a report, and certainly could not have been heard at the distance of 20 paces: it resembled the noise occasioned by the breaking of a very small glass tube. I imagined at first that the powder had not all taken fire, but the heat of the barrel soon convinced me that the explosion must have taken place; and after waiting near half a hour, on loosening the screw which closed the end of the long vent tube, the confined elastic vapours rushed

out with considerable force, and with a noise like that attending the discharge of an air-gun.

Having found means to confine the elastic vapour generated in the combustion of gunpowder, my next attempts were to measure its force. The principal objects I had in view were, first, to determine the expansive force of the elastic vapour generated in the combustion of gunpowder in its various states of condensation, and to ascertain the ratio of its elasticity to its density; and, secondly, to measure, by one decisive experiment, the utmost force of this fluid in its most dense state; that is to say, when the powder completely fills the space in which it is fired, and in which the generated fluid is confined. The dimensions of the barrel used in these experiments were as follow Diameter of the bore at its muzzle = 0.25 of an inch. Joint capacities of the bore, and of its vent tube, exclusive of the space occupied by the leathern stopper, = 0.08974 of a cubic inch. Quantity of powder contained by the barrel and its vent tube when both were quite full, exclusive of the space occupied by the leathern stopper, 24 grains Troy.

The elastic force of the fluid generated in the combustion of the charge of powder is measured by the weight by which it was confined, or rather by that which it was just able to move, but which it could not raise sufficiently to blow the leathern stopper quite out of the mouth of the bore of the barrel. This weight in all the experiments, except those which were made with very small charges of powder, was a piece of ordnance, of greater or less dimensions, or greater or less weight, according to the force of the charge; placed vertically on its cascabel, on the steel hemisphere which closed the end of the barrel; and the same piece of ordnance, by having its bore filled with a greater or smaller number of bullets, as the occasion required, was made to serve for several experiments.

It appears from 109 experiments, that in the afternoon of the 1st of July, 1793, the weight (which was a heavy brass cannon, a 24 pounder, weighing 8081 lbs. avoirdupois,) was not raised by 12 grains of powder, but that 13 grains raised it with an audible though weak report: that the next morning, July 2., at 10 o'clock, it was raised twice by charges of 12 grains: that in the morning of the 3d of July it was not raised by 12 grains, nor by 13 grains; but that 14 grains just raised it: that in the afternoon of the same day, two experiments were made with 14 grains of powder, in neither of which the weight was raised; but that in another experiment, in which 15 grains of powder were used, it was raised with a moderate report: that in the morning of the 8th of July, in two experiments, one with 15 grains, and the

other with 13 grains of powder, the weight was raised with a loud report; and in an experiment with 12 grains, it was raised with a feeble report: and, lastly, that in three successive experiments, made in the morning of the 17th of July, the weight was raised by charges of 12 grains. Hence it appears that under circumstances the most favourable to the developement of the force of gunpowder, a charge 12 grains, filling of the cavity in which it is confined, on being fired, exerts a force against the sides of the containing vessel equal to the pressure of 9431 atmospheres; which pressure amounts to 141,465 lbs. avoirdupois on each superficial inch.

I finish this paper by a computation, showing that the force of the elastic fluid generated in the combustion of gunpowder, enormous as it is, may be satisfactorily accounted for on the supposition that its force depends solely on the elasticity of watery vapour, or steam. It is certain that the heat generated in the combustion of gunpowder cannot possibly be less than that of red-hot iron. It is probably much greater, but we will suppose it to be only equal to 1000 degrees of Fahrenheit's scale, or something less than iron visibly red-hot in daylight. This is about as much hotter than boiling linseed oil, as boiling linseed oil is hotter than boiling water. As the elastic force of steam is just equal to the mean pressure of the atmosphere when its temperature is equal to that of boiling water, or to 212° of Fahrenheit's thermometer, and as its elasticity is doubled by every addition of temperature equal to 30 degrees of the same scale, with the heat of 242° its elasticity will be equal to the pressure of two atmospheres ; at the temperature of 272° it will equal four atmospheres ; and at two degrees above the heat of boiling linseed oil its elasticity will be equal to the pressure of 8192 atmospheres, or above eight times greater than the utmost force of the fluid generated in the combustion of gunpowder, according to Mr. Robins's computation. But the heat generated in the combustion of gunpowder is much greater than that of 602° of Fahrenheit's thermometer, consequently the elasticity of the steam generated from the water contained in the powder must of necessity be much greater than the pressure of 8192 atmospheres. Following up our computations on the principles assumed (and they are founded on the most incontrovertible experiments), we shall find that, at the temperature of 632°, the elasticity will be equal to the pressure of 16,384 atmospheres; at 662°, 32,768; at 692°, 65,536; and at 722°, the elasticity will be equal to the pressure of 131,072 atmospheres, which is 130 times greater than the elastic force

assigned by Mr. Robins to the fluid generated in the combustion of gunpowder; and about one sixth part greater than my experiments indicated it to be.

That the elasticity of steam would actually be increased by heat in the ratio here assumed, can hardly be doubted. It has absolutely been found to increase in this ratio in all the changes of temperature between the point of boiling water, I may even say of freezing water, and that of 280° of Fahrenheit's scale; and there does not appear to be any reason why the same law should not hold in higher temperatures.

A doubt might possibly arise with respect to the existence of a sufficient quantity of water in gunpowder, to fill the space in which the powder is fired, with steam, at the moment of the explosion; but this doubt may easily be removed. The best gunpowder, such as was used in my experiments, is composed of 70 parts in weight of nitre, 18 parts of sulphur, and 16 parts of charcoal; hence 1000 parts of this powder contain 673 parts of nitre, 173 parts of sulphur, and of charcoal 154 parts. Mr. Kirwan has shown that in 100 parts of nitre there are seven parts of water of crystallisation; consequently in 1000 parts of gunpowder, as it contains 673 parts of nitre, there must be 47 parts of water.

Charcoal exposed to the air has been found to absorb nearly one eight of its weight of water; and by experiments I have made on gunpowder, by ascertaining its loss of weight on being much dried, and its acquiring this lost weight again on being exposed to the air, I have reason to think that the power of the charcoal, which enters into the composition of unpowder, to absorb water remains unimpaired, and that it actually retains as much water in that state as it would retain were it not mixed with the nitre and the sulphur.

1160 grains Troy of apparently dry gunpowder, taken from the middle of a cask, on being exposed 15 minutes in dry air, heated to the temperature of about 200°, was found to have lost 11 grains of its weight. This shows that each cubic inch of this gunpowder actually gave out 2 grains of water on being exposed to this heat; and there is no doubt but that at the end of the experiment it still retained much more water than it had parted with.

If now we compute the quantity of water which would be sufficient, when reduced to steam under the mean pressure of the atmosphere, to fill a space equal in capacity to one cubic inch, we shall find that either that contained in the nitre which enters into the composition of one cubic inch of gunpowder as water of crystallisation, or even that small quantity

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