In the state to which it is now brought, the mould is exceedingly friable, and requires to be handled with becoming care. With the face downwards it is placed upon the flat cast-iron _floating-plate_, which, in its turn, is set at the bottom of a square cast-iron tray, with upright edges sloping outwards, called the "dipping pan." It has a cast-iron lid, secured by a screw and shackles, not unlike a copying machine. This pan having been heated to 400 deg., it is plunged into an iron pot containing the melted alloy, which hangs over a furnace, the pan being slightly inclined so as to permit the escape of the air. A small space is left between the back or upper surface of the mould, and the lid of the dipping-pan, and the fluid metal on entering into the pan through the corner openings, _floats_ up the plaster together with the iron plate (hence called the _floating-plate_) on which the mould is set, with this effect, that the metal flows through the notches cut in the edge of the mould, and fills up every part of it, forming a layer of metal on its face corresponding to the depth of the border, while on the back is left merely a thin metallic film. The dipping-pan, says Tomlinson, is suspended, plunged in the metal, and removed by means of a crane; and when taken out, is set in a cistern of water upon supports so arranged that only the bottom of the pan comes in contact with the surface of the water. The metal thus _sets_, or solidifies, from below, and containing fluid above, maintains a fluid pressure during the contraction which accompanies the cooling. As it thus shrinks in dimensions, molten metal is poured into the corners of the pan for the purpose of maintaining the fluid pressure on the mould, and thus securing a good and solid cast. For if the pan were allowed to cool more slowly, the thin metallic film at the back of the inverted plaster mould would probably solidify first, and thus prevent the fluid pressure which is necessary for filling up all the lines of the mould. Tomlinson concludes his description of these interesting processes by informing us that an experienced and skilled workman will make five dips, each containing two octavo pages, in the course of an hour, or, as already stated, at the rate of nearly ten octavo sheets a day.