This is by far the most valuable metal that has been brought into notice during the past few years. It has been long familiar to chemists, and as a component of German silver, electrum, and similar alloys, it has been in common use, but as an unalloyed coating for other metals it has only been employed for about ten years.
It is hard, not easily corroded by acids, and, unlike silver, it is entirely unaffected by sulphur. In addition to these valuable qualities it has one of special importance in some cases, and that is the ease with which a nickel surface slides over any other smooth body. Hence, for the sliding parts of telescopes, microscopes, etc., it has come into very general use, and it is not improbable that it will prove of great value in the case of slide valves, pistons, etc.
Nickel is almost always applied as a coating by the electroplating process, for instructions in which art we must refer our readers to any good work on the art of electro-metallurgy.
A foreign journal gives the following directions for nickel plating without a battery: To a solution of five to ten per cent, of chloride of zinc, as pure as possible, add sufficient sulphate of nickel to produce a strong green color, and bring to boiling in a porcelain vessel. The piece to be plated, which must be perfectly bright and free from grease, is introduced so that it touches the vessel as little as possible. Ebullition is continued from 30 to 60 minutes, water being added from time to time to replace that evaporated. During ebullition nickel is precipitated in the form of a white and be pliant coating. The boiling can be continued for hours without sensibly increasing the thickness of this coating. As soon as the object appears to be plated it is washed in water containing a little chalk in suspension, and then carefully dried. This coating may be scoured with chalk, and is very adherent. The chloride of zinc and also the sulphate of nickel used must be free from metals precipitable by iron. If during the precipitation the liquor becomes colorless, sulphate of nickel should be added. The spent liquor may be used again by exposing to the air until the contained iron is precipitated, filtering and adding the zinc and nickel salts as above. Cobalt also may be deposited in the same manner.