The soluble salts are, when in the hydrated condition, also red, but in the anhydrous condition are blue.
Cobalt chloride, CoC1 2, in the anhydrous state, is formed by burning the metal in chlorine or by heating the sulphide in a current of the same gas.
By dissolving it in concentrated sulphuric acid and warming the solution, the anhydrous salt is obtained.
Boron nitride BN is formed when boron is burned either in air or in nitrogen, but can be obtained more readily by heating to redness in a platinum crucible a mixture of one part of anhydrous borax with two parts of dry ammonium chloride.
Thus its non-liability to freeze (when not absolutely anhydrous, which it practically never is when freely exposed to the air) and its nonvolatility at ordinary temperatures, combined with its power of always keeping fluid and not drying up and hardening, render it valuable as a lubricating agent for clockwork, watches, &c., as a substitute for water in wet gas-meters, and as an ingredient in cataplasms, plasters, modelling clay, pasty colouring matters, dyeing materials, moist colours for artists, and numerous other analogous substances which are required to be kept in a permanently soft condition.
