Cyanogen and hydrocyanic acid, recognizable by their odour, indicate decomposable cyanides.
Carbon dioxide, recognized by turning lime-water milky, indicates decomposable carbonates or oxalates.
The bark of the horse-chestnut contains a greenish oil, resin, a yellow body, a tannin, C26 H 24012, existing likewise in the seeds and various parts of the tree, and decomposable into phloroglucin and aesciglyoxalic acid, C 7 H 6 O 3, also aesculetin hydrate, and the crystalline fluorescent compound aesculin, of the formulaC21H24013 (Rochleder and Schwarz), with which occurs a similar substance fraxin, the paviin of Sir G.
Chlorine, bromine, and iodine, each recognizable by its colour and odour, result from decomposable haloids; iodine forms also a black sublimate.
To form (1) oxides and nitric acids, (2) ammonia, (3) readily decomposable nitrides, (4) cyanides, (5) cyanamides.
In general these compounds are decomposable by heat, but some of them, such as those of gold, silver, copper and the alkali metals, even when heated above the boiling point of mercury retain mercury and leave residues of definite composition.
Mehner patented heating the oxides of silicon, boron or magnesium with coal or coke in an electric furnace, and then passing in nitrogen, which forms, with the metal liberated by the action of the carbon, a readily decomposable nitride.
The process may be accelerated by exhausting the desiccator; this so-called vacuum desiccation is especially suitable for the concentration of aqueous solutions of readily decomposable substances.
It may also be accomplished by calcination with ferrous sulphate, or other easily decomposable sulphates, such as aluminium sulphate.