The Romance of Modern Chemistry

TWO METALS BETTER THAN ONE pins are put in a solution containing tin, and the result is that a coating of this metal is deposited on the brass. Such a method of depositing one metal on another is very closely related to the process of electro-plating, When an electric current is passed between two metal rods or electrodes immersed in a salt solution, the salt is decomposed and the metallic constituent is deposited on one of the electrodes. Suppose now that the solution contains a salt of silver, and that we replace the rod on which the metallic constituent is deposited by a spoon made of some alloy, then on passing the current the usual thing happens, and we get a fine, coherent deposit of silver on the spoon ; the latter is electro-plated. In this way articles made of common metals or alloys may be plated with gold, silver, copper, or nickel. For example, we can protect steel articles, such as bicycle fittings, from atmospheric corrosion by plating them with nickel. Articles, on the other hand, which are to be used for the table or for ornament may be similarly coated with silver. Spoons and forks, for instance, are generally made of Britannia metal, an alloy containing mostly tin and antimony, or of German-silver, an alloy of copper, zinc, and nickel; when these articles are coated with silver they are less easily attacked by acid liquids, and at the same time their appearance is improved. Plating, after all, is a device for hiding the short- comings of one metal by covering it with another. There is, however, a second way of making good the deficiencies of a metal, and that is by mixing it thoroughly with another of different character. In what way the properties of one metal are modified by thus alloying it with a second may be best understood from a few examples. The ubiquitous penny piece is commonly known as “ a 74