Experiments.
1. Into a solution of nitrate of silver in distilled water immerse a clean plate or slip of copper. The solution, which was colorless, will soon begin to assume a greenish tint, and the piece of copper will be covered with a coating of a light gray color, which is the silver formerly united to the nitric acid, which has been displaced by the greater affinity or liking of the oxygen and acid for the copper.
2. When the copper is no longer coated, but remains clean and bright when immersed in the fluid, all the silver has been deposited, and the glass now contains a solution of copper.
Place a piece of clean iron in the solution, and it will almost instantly be coated with a film of copper, and this will continue until the whole of that metal is removed, and its place filled by an equivalent quantity of iron, so that the nitrate of iron is found in the liquid. The oxygen and nitric acid remain unaltered in quantity or quality during these changes, being merely transferred from one metal to another.
A piece of zinc will displace the iron in like manner, leaving a solution of nitrate of zinc.
Nearly all the colors used in the arts are produced by metals and their combinations; indeed, one is named chromium, from a Greek word signifying color, on account of the beautiful tints obtained from its various combinations with oxygen and the other metals. All the various tints of green, orange, yellow, and red, are obtained from this metal.
Solutions of most of the metallic salts give precipitates with solutions of alkalies and their salts, as well as with many other substances, such as what are usually called prussiate of potash, hydro-sulphuret of ammonia, etc.; and the colors differ according to the metal employed, and so small a quantity is required to produce the color that the solutions before mixing may be nearly colorless.