Some Uses of Electricity
The ability of the electric current to decompose a liquid and to deposit a metal constituent has practically revolutionized the process of printing. Formerly, type was arranged and retained in position until the required number of impressions had been made, the type meanwhile being unavailable for other uses. Moreover, the printing of a second edition necessitated practically as great labor as did the first edition, the type being necessarily set afresh. Now, however, the type is set up and a mold of it is taken in wax. This mold is coated with graphite to make it a conductor and is then suspended in a bath of copper sulphate, side by side with a slab of pure copper. Current is sent through the solution as described earlier, until a thin coating of copper has been deposited on the mold. The mold is then taken from the bath, and the wax is replaced by some metal which gives strength and support to the thin copper plate. From this copper plate, which is an exact reproduction of the original type, many thousand copies can be printed. The plate can be preserved and used from time to time for later editions, and the original type can be put back into the cases and used again.