the Force of Fired Gunpowder. 127 



grains of gunpowder, determined by weighing them in 

 air, and in water, is to the specific gravity of water as" 

 1.868 to I.OOQ. But if a measure whose capacity is one 

 cubic foot hold 1000 ounces of water, the same meas- 

 ure will hold just 1077 ounces of fine grained gun- 

 powder, such as I made use of in my experiments; that 

 is to say, when it is well shaken together. When it was 

 moderately shaken together, I found its weight to be 

 exactly equal to that of an equal volume, or rather 

 measure, of water. But it is evident that the weight of 

 any given measure of gunpowder must depend much 

 upon the forms and sizes of its grains. 



I shall add only one observation more, relative to the 

 particular appearances which attended the experiments 

 in which the elastic vapour generated in the combustion 

 of gunpowder was confined, and that is with regard to 

 a curious effect produced 'upon the inferior flat surface 

 of the leathern stopper, where it was in contact with the 

 generated elastic vapour. Upon removing the stopper, 

 its lower flat surface appeared entirely covered with an 

 extremely white powder, resembling very light white 

 ashes, but which almost instantaneously changed to the 

 most perfect black colour upon being exposed to the 

 air. 



The sudden change of colour in this substance, upon 

 its being exposed to the air, has led me to suspect that 

 the solid matter found in the barrel was not originally 

 black, but that it became black merely in consequence 

 of its being exposed to the air. The dirty gray colour it 

 appeared to have immediately on its being drilled out of 

 the cavity of the bore, where it had fixed itself, seems 

 to confirm this suspicion. An experiment made with a 

 very strong glass barrel would not only decide this 



