no CHEMICAL PROPERTIES AND COMPOSITION 



chanism of the explosion is explained by the fact that 

 in nitre 



>N-0_K, 



the oxygen combined with nitrogen is, according to p. 105, 

 in a strained position ; it is destined to combine with the 

 carbon, which, according to p. 107, is among the first in 

 point of evolution of heat of those elements that yield 

 gaseous products. The potassium is then free to combine 

 with the element with which its heat of combination is 

 greatest, sulphur, the reaction taking place in the follow- 

 ing way : 



This expression corresponds with the composition actu- 

 ally used : but in consequence of incomplete mixture other 

 reactions occur locally. 



(/3) Liquid mixtures. Besides the disadvantage just 

 mentioned, solid mixtures suffer from another, in that the 

 reaction on account of imperfect mixture and contact 

 cannot go fast, causing only a gradually propagated com- 

 bustion at a few metres per second, instead of the explo- 

 sive wave (Part I, p. 253) travelling at more than icoo 

 metres. The danger in handling liquid explosives thus 

 arising may be avoided in several ways. At the present 

 moment such a mixture is used e. g. in carbon and liquid air, 

 and perhaps the new resources in low temperatures and 

 liquefied gases will make available much better mixtures 

 still, such as those mentioned on p. 108. It may be added 

 that, if one of the components contains carbon, the inertia 

 of the affinity of carbon (p. 97) is favourable to safety, 

 although it does not hinder the development of an explo- 

 sive wave. Thus a mixture of ether with peroxide of 

 hydrogen up to 70 per cent, can be kept entirely without 

 danger, and is used by dentists, although it is undoubtedly 

 capable of violent explosion. 



(y) More complex compounds. (Smokeless gunpowder.) 



