EXPLOSIONS AND EXPLOSIVES. 777 



to be useful where a stronger explosive than ordinary gunpowder is 

 desired is known as Abel's picric powder ; this is a mixture of picrate 

 of ammonia and saltpeter, prepared in an ordinary powder-mill by the 

 processes just detailed. Picric acid (by means of which the picrate of 

 ammonia is obtained) is derived from the action of strong nitric acid 

 upon carbolic acid. This powder requires confinement to develop its 

 force, is not exploded by friction, and, as it absorbs no moisture by ex- 

 posure to the air, can be used and stored like gunpowder ; for the 

 ordinary uses of gunnery, however, it can never supersede its elder 

 brother. 



As has already been said, gunpowder burns, rapidly it is true, but 

 nevertheless the action is a true combustion. We now come to the 

 consideration of a new class of explosives, which do not burn, but 

 resolve themselves into their constituent gases immediately upon the 

 application of the force which suffices to bring about their disintegra- 

 tion. These are not mixtures like gunpowder, but definite chemical 

 compounds in which the carbon, oxygen, and hydrogen are held a 

 little way apart, as it were, by the nitrogen, but ready to rush together 

 at the first opportunity ; the explosion of one particle means generally 

 the contemporaneous explosion, or detonation, of the whole mass : 

 with such bodies confinement to any great extent is not necessary. 



Pre-eminent among these detonating substances for its use in min- 

 ing and engineering operations of a like character stands the compound 

 known as nitro-glycerine. This is manufactured in greatly increasing 

 quantities in many places, both in this country and in Europe, and its 

 use for the purposes above mentioned is becoming more and more 

 general. Its transportation in the liquid state being excessively dan- 

 gerous, it was for a long time but little used ; but, it having been 

 ascertained that it can be mixed with other materials and carried with 

 comparative safety, its field of usefulness has become greatly enlarged. 

 It is formed by the action of very strong nitric acid upon glycerine at 

 a low temperature, the resulting product being removed and washed 

 free of its impurities. 



Glycerine is a by-product of the stearine-candle manufacture, be- 

 ing separated from the stearic acid contained in animal fat upon the 

 application of superheated steam. It is subsequently redistilled until 

 its impurities are removed, in which condition it is proper to be used 

 in the manufacture of nitro-glycerine. Unfortunately, however, many 

 manufacturers do not restrain themselves to a pure quality of the glyc- 

 erine, but, using inferior ones (which are, of course, cheaper), make a 

 nitro-glycerine which is of a much more dangerous character than 

 should ever be used. 



The process of manufacture is as follows : The nitric acid is mixed 

 with twice the quantity of sulphuric acid, and both then mixed with 

 the glycerine ; the nitric acid acts upon the glycerine, leaving a quan- 

 tity of water free ; were the sulphuric acid not present, this water 



