ABSTRACT
The various bodies contained in the coal-tar are separated from each other by taking advantage of fact that each substance has its own boiling-point; that is, there is certain temperature, different for each body, at which it will rise into vapour. The coal-tar, as it is received from gas-works, is placed in large stills, capable, perhaps, of holding several thousand gallons, and usually made of wrought iron. Stills sufficiently good for purpose are commonly, constructed from worn-out boilers of steam engines. The chief colours-producing substances contained in coal-tar are benzol, toluol, phenol, naphthalene, and anthracene. The aniline which is present in tar is very small in amount, and if this ready-formed aniline were our only supply, it would be impossible to make colours from it on the industrial scale. The quantity of aniline obtained from coal-tar is very small compared to amount of coal used in which the respective weights of various products required in manufacture of mauve are arranged.
