2 FORCE OF EXPLOSIVES IN GENERAL. 



practice, in the form of useful work, a considerable amount 

 being absorbed in heating the surrounding medium, in creating 

 in it wave-motion, and in various other ways. For instance, in 

 blasting rock, the useful work consists partly in shattering the 

 rock, and partly in displacing the shattered masses. The 

 remaining energy is absorbed by work, owing to (1) incomplete 

 combustion, (2) compression and chemical changes induced in 

 the surrounding material operated on, (3) energy expended in 

 the cracking and heating of the material which is not displaced, 

 (4) the escape of gas through the holes and fissures caused by 

 the explosion. 



The calculation of the distribution of the energy of an 

 explosive between the mechanical work accomplished, the heating 

 of the surrounding medium, and the vibratory movement com- 

 municated to the ground or air, etc., is very complicated, and 

 will be treated of in a later portion of this work. 



A knowledge of the special properties of explosives enables 

 us to judge, more or less, which particular explosive is likely to 

 be suitable for a particular class of work. In popular language, 

 they are divided into " High " and " Low," and of these two 

 classes, Dynamite and Gunpowder may be taken as the par- 

 ticular types, but no hard and fast line can be drawn between 

 them. 



Generally speaking, we mean by " high " explosives, those in 

 which the chemical transformation is very rapid, and which 

 exert a crushing or shattering effect; a comparatively slow 

 chemical transformation and propelling effect being, on the 

 other hand, characteristic of a " low " explosive. 



In mercury fulminate we have an extreme instance of rapid 

 chemical transformation, accompanied by intense local action, 

 and other phenomena common to this class of explosives. 



The more common " high " explosives are bodies containing 

 a large amount of oxygen, and possessing a definite chemical 

 composition. 



They are produced by the action of nitric acid on organic 

 substances forming nitric ethers (nitroglycerin, nitromannite) 

 or nitro-substitution compounds (picric acid and its derivatives). 



In consequence of the intimate contact of the combustible 

 and the oxygen in such compounds, a more energetic and rapid 

 action is developed on explosion than that which would result 

 from a simple mixture. 



Perchloric ethers and mercury oxycyanide produce analogous 

 effects, as also ammonium nitrate, bichromate and perchlorate 

 (under certain conditions), the acid giving up its oxygen, and 

 the ammonia its hydrogen. 



Formerly the force of an explosive was deduced from the 

 weight of available oxygen which it contained; but this idea 

 is inaccurate, for oxygen does not necessarily enter into the 



