382 GENERAL DATA. 



It should also be ascertained whether the substance, when 

 subjected for several days to a series of shocks in conditions 

 similar to such as would arise during conveyance by sea or land, 

 occasions the separation of some of its components. 



These exudation tests are, above all, essential as regards 

 dynamites, as the separation of the nitroglycerin tends to make 

 them very dangerous. 



5. Shock. It should be tried whether the substance explodes 

 by the shock of a hammer on an anvil, or better still by the 

 fall of a given weight falling from various heights on a portion 

 of the substance placed on an anvil. 



An explosive should not explode through the shock or friction 

 of wood on wood or of wood on metal (bronze or iron). Some 

 substances do not explode by the shock of bronze on bronze, 

 but do so by iron on iron. 



The accidental introduction of some grain or fragment of 

 sand or other hard rock facilitates the explosion, especially by 

 friction. 



The action of the shock of bullets at different distances 

 should be studied, especially in the case of substances intended 

 for military operations. 



6. Immersion. The explosive substance is placed under 

 water without any covering for fifteen to twenty minutes. It 

 ought neither to, dissolve nor split up, nor give rise to the 

 separation of small liquid drops. This test is only applicable to 

 substances which are liable to be in contact with water when used. 



7. Heat. It is first ascertained whether the substance 

 becomes inflamed when in contact with an ignited body, and 

 how it burns in this condition. 



The influence of very slow progressive heating is also studied 

 in order to see whether it gives rise to the partial evaporation 

 of any of its components. 



We then proceed to more rapid heating, placing, for instance, 

 a small quantity of the substance in a thin metallic capsule, 

 which is laid on the surface of an oil or a mercury bath l main- 

 tained beforehand at a fixed temperature. It is ascertained at 

 what temperature the explosion takes place, and whether simple 

 burning or even progressive decomposition can take place at a 

 lower temperature. 



These general questions being defined, we proceed to the 

 study of the various groups and kinds of explosive substances. 

 Let it, however, be remembered that it is not intended to give 

 an individual and a practical history of each of them in all its 

 details, which would lead us too far ; but we especially wish to 

 point out the scientific data which characterise them by study- 

 ing the principal explosive bodies hitherto known, these bodies 

 being considered as typical of all similar substances. 



1 The capsule must then be made of platinum. 



