MODERN EXPLOSIVES 19 



particles is shown by the fact that the most powerful explo- 

 sive is not the most powerful detonator ; neither is it entirely 

 due to heat, since wet substances undergo detonation. The 

 probability is that the result is brought about by vibrations 

 of particular velocity which vary for different substances, 

 the decomposition being caused by the conversion of the 

 mechanical force into heat in the explosive, thus bringing 

 about a change in the atomic arrangement of the molecule. 

 According to Sir Frederick Abel's theory of detonation, 

 the vibrations caused by the firing of the detonator are 

 capable of setting up similar vibrations in the explosive, 

 thus determining its almost instantaneous decomposition. 



The most common and familiar of explosives is undoubt- 

 edly gunpowder, and although for military purposes it has 

 been largely superseded by smokeless powders, yet it has 

 played such an important part in the history of the world 

 during the last few centuries that apart from military uses 

 it is even now of sufficient importance to demand more than 

 a passing notice. 



Its origin, although somewhat obscure, was in all prob- 

 ability with the Chinese. Roger Bacon and Berthold 

 Schwartz appear to have rediscovered it in the latter 

 years of the thirteenth and earlier part of the fourteenth 

 centuries. It was, undoubtedly, used at the battle of Crecy 

 (1346) . The mixture then adopted appears to have consisted 

 of equal parts of the three ingredients sulphur, char- 

 coal, and nitre; but some time later the proportions, even 

 now taken for all ordinary purposes, were introduced, 

 namely : 



Potassium nitrate 75 parts 



Charcoal 15 " 



Sulphur 10 " 



100 parts 



Since gunpowder is a mechanical mixture, it is clear that 

 the first aim of the maker must be to obtain perfect incor- 

 poration, and, necessarily, in order to obtain this, the 



