In consequence of its great affinity for oxygen, potassium must be kept in some fluid destitute of that element, such as naphtha.
Caution!—As the globules of potassium after conversion into potash, when thrown on ice or water burst, strewing small particles of caustic hot potash in every direction, the greatest care should be taken to keep at a sufficient distance whilst performing the above experiment.
Saltpetre, or nitre, is a compound of this metal (or rather its oxide) with nitric acid. It is one of the ingredients of gunpowder, and has the property of quickening the combustion of all combustible bodies.
Mix some chlorate of potash with lump sugar, both being powdered, and drop on the mixture a little strong sulphuric acid, and it will instantly burst into flame. This experiment also requires caution.
Want of space precludes us from considering the individual metals and their compounds in detail; it must suffice to describe some experiments showing some of their properties.
The different affinities of the metals for oxygen may be exhibited in various ways. The silver or zinc tree has already been described, [page 357].
EXPERIMENTS.
1. Into a solution of nitrate of silver in distilled water immerse a clean plate or slip of copper. The solution, which was colourless, will soon begin to assume a greenish tint, and the piece of copper will be covered with a coating of a light grey colour, 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 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.