The required quantities of sulphur and charcoal are thoroughly pulverised, and intimately mixed, by being rolled for about four hours in a cast-iron drum, with numerous small brass balls, at a speed of about 28 revo • lutions a minute. When the mixture is complete, the powdered sulphur and charcoal are removed from the drum, and a proportionate quantity of saltpetre is added. Great care must be used in weighing out the various ingredients, according to the quality of the powder required, as upon that, and the complete mixing of the materials, the success of the manufacture depends.
The powder is put in a mixing machine, which is a leather drum, in which are placed numerous small bronze balls. The machine revolves at 25 to 30 revolutions a minute, and in about 4 hours' time the mixing is complete.
The powder, having been damped and pressed into cakes, must then be crushed to the required size of grain. It is first roughly broken into lumps by small mallets; it is then fed into the granulating machine, which is caused to revolve for 35 or 40 minutes, at about 10 revolutions a minute. A small stream of water enters the granu-lator; the movement of the machine rolling the damp grains constantly among the dry meal powder causes the latter to adhere to their surface, and each grain is thus increased by concentric layers. When the small meal powder is all absorbed by the action of the gianu-lator, the material is placed in a barrel ready for equalisation.
The grains as they come from the granulator are of various sizes; they are therefore sifted over two leather or parchment sieves, one of which is pierced to separate the grains which are too large, whilst the other allows all the dust to pass through, retaining only the grains which are of the desired size. The small refuse powder which has passed through the sieve is again placed in the granulator, and acted upon as before described.
The powder is placed in a cask or barrel, which revolves on its axis at about 40 revolutions a minute; by the friction of the grains against each other they become round, smooth, and polished, in which state the powder will bear the shaking and friction of carriage without injury, and is less likely to absorb moisture than when in rough and angular grains.
The powder must not be too rapidly dried, a temperature commencing at about 66° F., and gradually increased to 130° or 140° F., is a safe one; the operation requires 3 to 4 hours, and is best performed in a room (warmed by steam pipes or hot-air flues. The powder is then fit for use, and may be packed in sacks, to be afterwards placed in casks, or in double casks; sporting powder is usually packed in tin canisters. A much more complete account is given in Spons' Encyclopaedia.