To obtain a positive copy a cast has to be taken from a negative or reverse. This negative is called the mold or matrix, and can be of plaster, glue, wax, or other compositions. There are a number of processes in use, but the Adams process (no relation to the author) will give a boy a clear idea of this electro-chemical and mechanical art. This process was patented in 1870, and is said to give a perfect conduction to wax and other molds, with greater certainty and rapidity than any other, and will accomplish in a few minutes that which plumbago (black-lead) alone would require from two to four hours to effect. As applied to the electrotyping of type, and cuts for illustration, the warm wax impression is taken by pressing the chase or form of type into a bed of wax by power or hydraulic pressure. Then remove it, and while the wax is still warm, powdered tin, bronze, or white bronze powder is freely dusted all over it with a soft hair-brush, until the surface presents a bright, metallic appearance. The superfluous powder is then dusted off, and the mold is immersed in alcohol, and afterwards washed in water to remove the air from the surface. It is then placed in the copper bath and the connection made from the negative pole to the face of the mold, so that the current will flow over its entire surface. A deposit of copper will quickly appear, and become heavier as the mold is left in longer. When a mold has received the required deposit it should be taken from the bath and the copper film removed from it. This is done by placing the mold in an inclined position and passing a stream of hot water over the back of the copper film. This softens the wax and enables one to strip the film off, taking care at the same time not to crack or bend the thin copper positive. The thin coating of wax, which adheres to the face of the copper, can be removed by placing it, face up, on a wire rack and pouring a solution of caustic potash over it, which, in draining through, will fall into a vessel or tank beneath the rack. The potash dissolves the wax in a short time, and the electro-deposited shell may then be rinsed in several changes of cold water, or held under the faucet until thoroughly freed from the caustic. As many, if not all, of the chemicals used in the various plating processes, and also the cleaning fluids, are highly poisonous, great care should be taken when handling them. Do not let the fingers or hands come in contact with caustic solutions or cyanide baths. Never use any of these solutions if you have recently cut your fingers or hands, and do not allow the cyanides or caustics to get under the finger-nails. Never add any acid to liquids containing cyanide or ferro-cyanide while in a closed room. This should always be done in the open air, where the fumes can pass away, for the gases which rise from these admixtures are poisonous when inhaled. Chapter XII MISCELLANEOUS APPARATUS