PULVERIZING AND MIXING THE INGREDIENTS.
Pulverizing and mixing the ingredients.
The ingredients are generally pulverized in copper drums, capable of holding 224 kilogrammes. Part of the charcoal is mixed with the sulphur, and part of the sulphur with the saltpetre. They are then put into separate drums, which revolve about twenty-five times per minute for three hours, and in which are about 500 gun-metal or bronze balls, the size of good large marbles. The ingredients are brought to the most minute state of division by these means, and are then mixed all together, for one hour, in similar drums covered with leather, containing wooden balls.
INCORPORATING PROCESS.
Incorporation.
The fine powder thus obtained is sometimes merely moistened, so as to form a stiff paste, and passed through rollers, the cake formed, being dried and granulated. The incorporating cylinders are used occasionally, but the more usual plan adopted on the Continent to effect this operation is the stamping-mill, which requires a short description. It is nothing more nor less than the pestle-and-mortar principle, each mill consisting of from six to twelve bronze or wooden mortars bedded in the floor of the building; they are the shape of the frustum of a cone, the mouth being much narrower than the base; the pestles, or stampers as they are called, are made of wood, shod with either very hard wood or bronze, on which project wooden teeth about twelve inches long; a vertical movement is imparted to them by a shaft worked by the water-wheel having similar teeth attached; in its revolution it raises the stamper about eighteen inches, which falls again as the projection is disengaged, twenty five times in a minute. This operation is carried on for twelve hours, during which period the charge (about 15lbs.) is moistened at intervals, and routed up with a copper-shod spud; at the end of this time the cake is taken out, and left to dry and harden; it seldom receives any pressure—although, in some manufactories, presses are being erected.
GRANULATING.
Granulation.