material. Both the India and the artificial products are mixed with hot water, which takes up the salts, leaving the earthy matters behind; 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 over burned. 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 ordinary use; it being of a bluish-black tinge, somewhat elastic and slightly resonant when struck lightly with the finger, with the appearance of the woody fiber clear and distinct.
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 desired 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 saltpeter is mixed with them, and the whole mass placed in the incorporating 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 passing 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