~Quantity pressed.~ ~Amount of pressure.~ About 800 lbs. of the meal is put into this box while the plates are in the position we have described. When full, the slips are withdrawn, the plates being then only separated by the powder between them: the lid is now firmly screwed down, and the box turned over by an arrangement of pulleys, so that the plates which were vertical will now be horizontal. The present upper side is then unscrewed, and a travelling crane, moving on a rail overhead, is lowered till the claws attached to it hook on to two trunnions fixed on the sides of the box; it is now hoisted by means of a handwheel windlass, and the box being suspended, is pushed easily by means of the rail, and deposited in this position on to the table of the ram under the press block. The pumps are now set in motion by a water-wheel, and are allowed to work up to the required pressure, which is about seventy tons to the square foot; it is then conveyed from under the block in the same manner, and very easily unloaded. The press cake is then taken out in layers between each plate, resembling dark pieces of slate, about half an inch in thickness. After a day or so, this hardens so much as to be difficult to break, and the appearance of the fracture resembles that of the finest earthenware. Many important advantages are gained by this pressure, of which the following are the principal:-- ~Reasons for pressure.~ First, the density of the powder is increased, which prevents it falling to dust in transport, or by rough usage. Secondly, its keeping qualities are improved, for it withstands the action of the atmosphere, and absorbs less moisture than a porous light powder. Thirdly, it produces more grain in the manufacture than mill cake; and a less proportion, consequently, is lost in dust. Fourthly, a closer connection of the ingredients is obtained. Fifthly, a greater volume of inflammable gas is produced from a certain bulk, than from a corresponding bulk of lighter powder. ~Disadvantages of pressure.~ The range, however, is lessened, from a greater quantity being blown out of a gun unignited; but this small loss is more than counterbalanced by the former advantages, and actually it is only perceptible in newly-made powder; for a light, porous powder soon loses its superior range from its absorption of moisture, while that of the dense powder remains unaltered. GRANULATING THE PRESS CAKE. ~Mode of granulation.~ ~Screening.~