270 



Mr. Mallet on the Physical Conditions 



Table XII. 



In round numbers, therefore, 3 lbs. of gun-cotton will do the work of 8 lbs. 

 of gunpowder ; but its effects may be enormously more destructive upon the 

 gun, though producing only equal effect upon the shot. 



246. As stated at the commencement, the question of stress upon cannon, 

 resolves itself into one of maximum pressure per square inch. The researches 

 of Piobert have shown, that as a determinate time is necessary before the inertia 

 and compressibility of the shot can admit of its sensible motion, so this maximum 

 pressure (with all other conditions the same) is greatly increased, and the 

 maximum more rapidly reached, from the first instant of ignition, in proportion 

 as the powder is of a quality to burn more rapidly : so that, carried to its 

 extreme limit, as in the firing of some of the fulminating compounds, the gun 

 is burst before the shot is sensibly moved, and the velocity attained by the latter 

 is very sliglit. 



247. In order to determine, in an approximate way, the relative maximum 

 mean pressures of the gases from gunpowder and from gun-cotton at different 

 moments of the traject of the shot along the chase, — equivalent charges, viz., 

 eight grammes of gunpowder, and three of gun-cotton, were fired successively 

 with the same shot, from guns of various length, namely, 



64, 49, 38, 29, 22, 16, 11, 7, 5, and 4 



calibers in length, and the velocities of the shot, measured by the balistic pen. 

 dulum, 



