the Force of Filled Gtmpowder. 163 



force depends solely on the elasticity of watery vapour, or 

 steam. 



It has been shewn 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 1790, 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 i 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 presently shew that the water, existing in 

 the powder as water, is abundantly sufficient for generat- 

 ing this steam), if we know the heat communicated to 

 this steam in the combustion of powder, we can com- 

 pute the elasticity it requires by being so heated. 



Now it is certain that the heat generated in the com- 

 bustion 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 Fahren- 

 heit's scale, or something less than iron visibly red-hot in 

 daylight. This is about as much hotter than boiling lin- 

 seed 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 2i2°-|-30°= 242^ its elasticity 

 will be equal to the pressure of 2 atmospheres; at the 



