VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. ,173 



contracted that the bullet which is next to the powder may stick fast in it. I ought 

 to add, that though the bullets are of the common size, and are always consider- 

 ably less in diameter than the bore, means are used which effectually prevent the 

 loss of force by windage ; and to this last circumstance it is doubtless owing, in a 

 great measure, that the charge appears to exert so great a force in propelling the 

 bullets. That the conical form of the lower part of the bore, where it unites with 

 the chamber, has a considerable share in producing this extraordinary effect, is 

 however very certain, as I have found by experiments made with a view merely to 

 ascertain that fact. 



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 has been shown by a variety of experiments made in 

 England and in other countries, and lately by a well-conducted set of experiments 

 made in France by M. de Betancour, and published in Paris under the auspices of 

 the Royal Academy of Sciences, in the year 179O, that the elasticity of steam is 

 doubled by every addition of temperature equal to 30 degrees of Fahrenheit's ther- 

 mometer. Supposing now a cavity of any dimensions, equal in capacity to 1 cubic 

 inch, for instance, to be filled with gunpowder, and that on the combustion of the 

 powder, and in consequence of it, this space is filled with steam (and I shall pre- 

 sently show that the water, existing in the powder as water, is abundantly suffi- 

 cient for generating this steam) ; if we know the heat communicated to this steam 

 in the combustion of powder, we can compute the elasticity it acquires by being so 

 heated. 



Now 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 some- 

 thing less than iron visibly red-hot in day-light. 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 tem- 

 perature 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 212° + 30° = 242° its elasticity will be equal 



* Having, by a fallacious mode of comparison applied to his experiments, raised the force of fired 

 gunpowder to a monstrous degree, the author now has recourse to a most preposterous invention to 

 account for it, viz. moisture in the powder! whicl^has always heretofore been found greatly to injure 

 and depress the strength of that substance. 



f We have not been able to discover that this rate of increase, in the strength of the steam, is ac- 

 cording to the scale in Betancour's experiments. An account of these experiments, with the table of 

 corresponding temperature and strength of the steam, may be seen at the end of Dr. Hutton's Philos, 

 Dictionary, and may doubtless be found in other places in this country. Now in this table it does not 

 appear that the law of the increase of strength is at all conformable to the law above-mentioned, or that 

 the strength is doubled by the addition of any constant number of degrees of heat whatever. These 



