the Force of Fired Gunpowder. 167 



That this estimation is not too high is evident from 

 the following experiment. 1160 grains Troy of ap- 

 parently 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 

 II grains of its weight. This shews 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 re- 

 tained 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 i cubic inch, we shall find that, either that 

 contained in the nitre which enters into the composition 

 of I cubic inch of gunpowder as water of crystallization^ 

 or even that small quantity which exists in the powder 

 in the state of moisture, will be much more than suffi- 

 cient for that purpose. 



Though the density of steam has not been determined 

 with that degree of precision that could be wished, yet 

 it is quite certain that it cannot be less than 2000 times 

 rarer than water, when both are at the temperature of 

 212°. Some have supposed it to be more than 10,000 

 times rarer than water, and experiments have been made 

 which seem to render this opinion not improbable ; but 

 we will take' its density at the highest estimation, and 

 suppose it to be only 2000 times rarer than water. As 

 I cubic inch of water weighs 253.175 grains, the water 

 contained in i cubic inch of steam at the temperature 

 of 212° will be 2 0^0^0 P^''^ o^ ^53-175 grains, or 0.12659 

 of a grain. 



But we have seen that i cubic inch of gunpowder 



