In order, as much as possible, to guard against any explosion spreading, above each bed, placed so as just to clear the runners, is suspended or balanced a copper tank, holding about forty gallons of water. On one side of the tank is fixed a small shaft, which communicates with similar cisterns over the beds of the mills on either side. The other end of the tank rests on a flat board, which is subjected to a great part of the force of an explosion. This consequently lifts, disengaging the support of the tank, the contents of which drench the bed which has just exploded, thereby putting out all fire, and cooling the machinery, besides having a similar effect on the mills right and left, preventing, by this means, any extension of fire. INCORPORATING THE INGREDIENTS. ~Incorporation.~ ~Mill cake.~ ~Proof of mill cake.~ The charge is spread pretty evenly over the surface of the bed, and moistened with from four to six pints of distilled water; the quantity varying according to the state of the atmosphere; the runners are then set in motion, and run from seven to eight revolutions per minute for three and a half hours, during which time the powder is often routed up by a copper-shod spud, and watered slightly with a fine rose watering pot, according to the experience of the millman; at the end of this time the mixture is thoroughly incorporated, possesses all the chemical properties of Gunpowder, and is taken off the bed in the form of a cake, varying from a quarter to half an inch in thickness, and of a blackish-grey colour. This is called “Mill Cake,” and when broken, the fracture should exhibit the same uniform appearance, without presenting any sparkling or yellow specks; should this, however, be the case, it is a sign of the ingredients not being sufficiently incorporated. In this stage it undergoes certain proofs; samples of the cake are taken from every charge that is worked, dried in an oven, and granulated; half a drachm of this is fired in a vertical eprouvette, which it ought to raise 3.5 inches; and half an ounce is flashed on a glass plate. If very little residue or ash is left, it is an additional proof of its being well incorporated, and that the millman has done his work properly. ~Importance of incorporation.~ Incorporation is by far the most important process in the manufacture of Gunpowder; for, however carefully the other part of the fabrication is carried on, should there be a failing in this, the powder will be worth nothing. ~Object of manufacture.~