EXPLOSIVE MIXTURES 107 



heat of formation of nitric oxide, recurs in the nitro-deri- 

 vatives and nitrates, such as nitromethane and methyl 

 nitrate 



and HoCON/ 

 ^O 



which contain the nitro group NO 2 . 



The strained position of oxygen in combination with 

 chlorine shows itself in the explosive character of the 

 chlorates and perchlorates, which all contain the chlorine- 

 oxygen linkage. 



It may be added that the combination of carbon and 

 nitrogen which causes cyanogen to be explosive, exists also 

 in the true nitro-compounds, such as nitromethane. The 

 list of explosive linkages is therefore : 



0-0, N=N, C=C, 



H Sb, H As, O N, 0-C1, 



N Cl, N S, N-Se, 



C_S, C N, C Ag. 



(b) Explosive Mixtures. 



Two elements. In what precedes, the cause of explosive 

 character was regarded as a strained atomic combination, 

 the freeing of which produces a sudden reaction. In the 

 reverse way a mixture may lead to explosion if it affords 

 opportunity for new atomic combinations. Starting again 

 with the simplest case, this will be a mixture of two 

 elements which can combine with large evolution of heat 

 and yield gaseous products, especially if the elements are 

 taken in the solid or liquid state. The essentials are thus, 

 miscibility, evolution of heat, initial solid or liquid state, 

 and production of gas. With regard to evolution of heat, 

 choice may be made by means of the table on p. 93. For 

 metals the highest values are obtained by combination 

 with fluorine, chlorine, oxygen, and sulphur ; these, how- 



