EXPLOSIVES 



103 



but nine simple bonds, as in the centric formula (Part II, 

 p. 96) would give 



9 (C C) = -9x5-7= -5i-3' 

 which comes fairly near to the observed value. 



The relations are not quite exact, and it is not to be 

 expected they should be, for, as will be seen later, the 

 presence of one element affects the affinity of another, e.g. 

 the substitution of each new chlorine atom in methane 

 produces a lessened heat effect ; the numbers are as follows : 



CH 4 CH 3 C1 CH 2 C1 2 CHC1 3 CC1 4 

 17-2 19-2 24-6 20-9 17-8 



Difference +2 +5-4 ~ 3'7 3* 1 - 



2. Constitution of Explosives. 



Explosives are characterized by the fact that they cause 

 a sudden increase of pressure. If a chemical reaction is 

 concerned in it, it is necessary that it should take place 

 rapidly and with a large increase of volume and tempera- 

 ture. (See Part I, p. 251.) The essential factors in this 

 process were discussed, and attention was paid on p. 253 

 to the velocity of explosion. We shall restrict ourselves to 

 considering the pressure, and especially to the part played 

 by evolution of heat, noting that the pressure theoretically 

 depends on the following relation : 



where V l and F 2 are the volumes at o and one atmosphere 

 before and after the explosion, and t the rise of temperature 

 caused by the production of heat at constant volume. 



F 



Since ^- can only be large when the products of ex- 



"i 

 plosion are gaseous, two categories must be distinguished 



y 



in regard to this effect, according as the factor -^ is of 



" 



