174 EXPLOSIVES 



these being saltpeter (niter or potassium nitrate). When 

 saltpeter is thoroughly mixed with a combustible substance 

 such as charcoal, the mixture will burn without being in 

 direct contact with the air, producing a gas which expands 

 very rapidly. An explosive prepared in this way is ordi- 

 narily termed gunpowder. Oxygen may be obtained from 

 saltpeter heated properly with sulphuric acid, the resulting 

 product being nitric acid, which contains all the original 

 oxygen of the saltpeter. Such substances as cotton, starch, 

 and glycerin are converted by the action of nitric acid 

 into high explosives much more powerful than gunpowder 

 and are known as guncotton, nitrocellulose, and nitro- 

 glycerin. Nitric acid treated with alcohol will dissolve such 

 metals as silver and mercury, forming compounds still more 

 violent and sensitive in their explosive effects. The com- 

 mercial product of this process is fulminate of mercury. 



As to effect, explosives may be divided into two classes: 

 slow or propulsive, such as gunpowder, which generate 

 pressure comparatively slowly; high or disruptive, such as 

 nitroglycerin or fulminate of mercury, which generate pres- 

 sure instantaneously. Propulsive explosives are of value 

 in firearms, quarry work, and occupations in which the 

 intention is to move material rather gradually and not 

 tear it to pieces. Disruptive explosives can be used only 

 where the intention is to destroy and shatter. 



Gunpowder. A mixture of charcoal and saltpeter alone 

 is not easily fired. The addition of sulphur greatly facili- 

 tates ignition. A combination of seventy-five parts salt- 

 peter, fifteen parts charcoal, and ten parts sulphur, finely 

 ground, is gunpowder, the simplest and most common 

 commercial explosive. Gunpowder was invented about 

 the year 1250. Credit for its invention has been given to 

 Bertholdt Swartz, a German monk, and also to Roger 

 Bacon of England. Some are of the opinion that it origi- 

 nated in China. Its first use as a propelling agent has been 

 ascribed to the Moors and Saracens in the fourteenth century. 



