652 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



tery was then sent along the wire, as a preliminary experiment had shown me 

 would, by making the wire red-hot, inflame the powder. The glass globe with- 

 stood the explosion, and of course retained whatever gases were generated ; its 

 interior was thinly coated with quicksilver in a very divided state. A bent glass 

 tube was now screwed to the stop-cock of the brass cap, which being introduced 

 under a glass jar standing in the mercurial bath, the stop-cock was opened. 

 Three cubical inches of air rushed out, and a 4th was set at liberty when the 

 apparatus was removed to the water-tub. The explosion being repeated, and the 

 air all received over water, the quantity did not vary. To avoid an error from 

 change of temperature, the glass globe was, both before and after the explosion, 

 immersed in water of the samel temperature. It appears therefore, that the JOgr. 

 of powder, produced 4 cubical inches only of air. 



To continue the comparison between the mercurial powder and gunpowder, 10 

 gr. of the best Dartford gunpowder were in a similar manner set fire to in the 

 glass globe : it remained entire. The whole of the powder did not explode, for 

 some complete grains were to be observed adhering to the interior surface of the 

 glass. Little need be said of the nature of the gases generated during the com- 

 bustion of gunpowder : they must have been, carbonic acid gas, nitrogen gas, 

 sulphureous acid gas, and, according to Lavoisier,* perhaps hydrogen gas. As to 

 the quantity of these gases, it is obvious that it could not be ascertained ; because 

 the 2 first were, at least in part, speedily absorbed by the alkali of the nitre, left 

 pure after the decomposition of its nitric acid. 



^ 8. From the experiments related in the 4th and 5th §, in which the gun- 

 powder proof and the gun were burst, it might be inferred, that the astonishing 

 force of the mercurial powder is to be attributed to the rapidity of its combustion ; 

 and, a train of several inches in length being consumed in a single flash, it is 

 evident that its combustion must be rapid. From the experiments of the 6th and 

 7th §, it is sufficiently plain that this force is restrained to a narrow limit; both 

 because the block of wood charged with the mercurial powder was more shattered 

 than that charged with the gunpowder, while the sand surrounding it was least 

 disturbed; and also because the glass globe withstood the explosion of lOgr. of 

 the powder fixed in its centre : a charge I have twice found sufficient to destroy old 

 pistol barrels, which were not injured by being fired when full of the best gun- 

 powder. It also appears, from the last experiment, that lOgr. of the powder, 

 produced by ignition 4 cubical inches only of air ; and it is not to be supposed 

 that the generation, however rapid, of 4 cubical inches of air, will alone account 

 for the described force ; neither can it be accounted for by the formation of a little 

 water, which, as will hereafter be shown, happens at the same moment : the quan- 

 tity formed from 10 gr. must be so trifling, that I cannot ascribe much force to 

 the expansion of its vapour. The sudden vaporization of a part of the mercury, 

 seems to me a principal cause of this immense, yet limited force ; because its limi- 

 * See Lavoisier, Traitc elementaire, p. 527. — Orig. 



