The insoluble salts are rose-red or violet in colour.
It is insoluble in water, while its salts are readily soluble.
Certain substances, such as the precious metals, are quite insoluble in the bead, but float about in it.
In a scientific definition the compounds of fatty acids with basic metallic oxides, lime, magnesia, lead oxide, &c., should also be included under soap; but, as these compounds are insoluble in water, while the very essence of a soap in its industrial relations is solubility, it is better to speak of the insoluble compounds as " plasters, " limiting the name " soap " as the compounds of fatty acids with soda and potash.
It is almost insoluble in water, but mixes in all proportions with absolute alcohol, ether, benzene and various oils.