EXPLOSIONS AND EXPLOSIVES. 775 



material. Both the India and the artificial products are mixed with 

 hot water, which takes up the salts, leaving the earthy matters be- 

 hind ; this liquid is then evaporated, the saltpeter crystallizing as a 

 fine white powder ; if the original be very crude, this product is again 

 subjected to a similar process. 



The charcoal requires more care in its preparation than either of 

 the other ingredients, as upon its quality depends largely the violence 

 of the action of the powder ; the more nearly pure carbon it is, the 

 better will be the result. It is made from some very light wood, such as 

 the black alder or willow, as these contain much carbon, and but little 

 ash : small pieces of these woods, stripped of their bark, are placed 

 in a retort which is kept at a uniform heat ; the vapors are allowed a 

 free exit, and the roasting is kept up until the experienced eye of the 

 workman warns him that it is time to withdraw the charge, lest it be 

 overburned. The entire contents of the retort are removed at once, 

 and covered in air-tight drums, where the charcoal is left to cool. 

 Thus prepared, charcoal is quite a different material from that in ordi- 

 nary use ; it being of a bluish-black tinge, somewhat elastic and 

 slightly resonant when struck lightly with the finger, with the appear- 

 ance of the woodv fiber clear and distinct. 



m 



The sulphur is prepared from its ore, by roasting the latter in a 

 retort, the vapors given off being condensed, and the resulting liquid 

 run into molds, and allowed to harden. 



Having procured the materials of proper fineness and in the de- 

 sired proportions, the sulphur and charcoal are placed in a revolving 

 cylinder with cylindrical rollers inside, by the action of which they 

 are broken up into small pieces. These are then transferred to a 

 similar cylinder containing bronze or zinc balls, in which they become 

 very highly pulverized. When this is fully accomplished, the salt- 

 peter is mixed with them, and the whole mass placed in the incorpo- 

 rating mill, being kept moist enough to be like dough, but still not 

 too wet, as that would interfere with its proper mixture. This mill 

 consists of two heavy iron wheels, revolving at the extremities of an 

 horizontal axis, the whole being revolved about a vertical axis in the 

 center of a cast-iron bed, surrounded with wooden sides. As this 

 upright axis revolves, the wheels move about their own axes, having 

 at the same time a forward motion, which causes the powder to be 

 both mixed and pressed at the same time ; in this manner, the mixture 

 is rendered much more intimate than by the old method of stamping, 

 in which the ingredients were placed in huge wooden mortars, and 

 subjected to the action of heavy pestles of the same material. When 

 sufficiently mixed, the mill-cake, as it is then called, is allowed to dry ; 

 after which it is taken to the breaking-down machine, where, on pass- 

 ing between heavy wooden rollers, it is broken into small fragments. 

 The next step is to subject it to the action of the press ; this is an 

 horizontal wooden trough in which are placed (about an inch and a 



