Theory of Gunpowder. 511 



Gp = 1-000 grm. 

 Sp = 0-964 „ 

 G, = 0-6806 „ 

 S, = 1-50 „ 

 V = 193-1 cubic centims. 

 t = 3340° C. 

 By substituting them in the formula, we obtain for p^ the value 

 4373-6. 



Calculating the pressure with the assumption of the specific gra- 

 vity of the residue at ordinary temperatures (2-35), we obtain 

 ioTpQ the value 3414-6. Hence about 1000 of the 4374 atmo- 

 spheres are due to the expansion caused by the heating of the 

 powder residue. 



A powder of the composition of that investigated by us, which 

 explodes in a gun behind the projectile, can never exert a press- 

 ure of 4500 atmospheres, in consequence of the unavoidable 

 loss of heat in the combustion. Whether essential changes in 

 the decomposition of powder occur if it explodes freely, or at 

 high pressure in the gun, might be easily ascertained from the 

 composition of the residue deposited in the gun, or from the 

 composition of the gases. If it be shown that under these cir- 

 cumstances the decomposition is. essentially the same, many 

 previous assumptions as to the pressure exerted in guns must 

 depend on very faulty premises, for the best artillery works give 

 this pressure at from 50,000 to 100,000 atmospheres*. 



These experiments give us at the same time the means of de- 

 termining the maximum mechanical effect of powder, that is, the 

 theoretical work which it performs when its gases expand under 

 a pressure corresponding to their respective volume in a space 

 supposed to be impervious to heat. 



Let aiflgffga, (fig. 5) be the space filled by the powder Gp, 

 a^a^a.^a^ the volume occupied by the residue G^, and a, a^Oc^a^ 



C C 

 the volume t'o= ^— -^ occupied by the gases in the moment 



bp O^ 



of the combustion, in which volume the pressure p prevails, 

 which has just been determined ; lastly, let aa^a^a be the space 

 occupied by the gases after they have expanded to the pressure/Ji. 

 Further, if c a^ a^c be the infinitely small expansion of the residue, 

 the work effected during this expansion under the pressure /?„ 

 will be PqcIv, and the total work which the gas effects in its total 

 expansion will be 



Work = j pdv. 



%Jvq 



* Piobcrt, Trailed' Artilterie, 1847, p. 322. 



