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The valuable constituents actually extracted are then these: benzene, toluene, xylene, naphthalene, anthracene, and phenol or carbolic acid. One ton of Lancashire coal, when distilled in gas retorts, yields about 12 gallons of coal-tar. Let us now learn what those 12 gallons of tar will give us in the shape of hydrocarbons and carbolic acid, mentioned as extracted profitably from tar.
This pure anthracene exhibits the phenomenon of fluorescence, that is, it not only looks white, but when the light falls on it, it seems to reflect a delicate violet or blue light. Our table shows us that from the 12 gallons of tar from 1 ton of coal we may gain 2-1/4 lb. of 20 per cent. Alizarin paste.
Naphthol Yellow is of course a naphthol colour, whilst Vermilline Scarlet is a dye containing both naphthylamine and naphthol. You see the quantities of these dyes, namely 7 lb. of Scarlet and 9-1/2 lb. of the Naphthol Yellow. The amount of pure anthracene obtained is 1/2 lb.
The number of coal-tar colours is thus very great, and the variety also. Adjective Colours. As regards the artificial coal-tar adjective dyestuffs, the principal are Alizarin and Purpurin. These are now almost entirely prepared from coal-tar anthracene, and madder and garancine are almost things of the past.
The naphtha on redistillation yields benzine, from which are prepared some of our most beautiful dyes; the dead oil, as the less volatile portion is termed, furnishes carbolic acid, used as a disinfectant and antiseptic, together with anthracene and naphthaline; all three substances the starting points of new series of coloring matters.
Separate the residuum in as many definite parts as possible, bottle and label, and keep accurate records as to process, weights, etc., so a reproduction of the experiment can at any time be made: Gelatine, 4 lbs.; asphalt, hard Cuban, 10 lbs.; coal-tar or pitch, 10 lbs.; wood-pitch, 10 lbs.; Syrian asphalt, 10 lbs.; bituminous coal, 10 lbs.; cane-sugar, 10 lbs.; glucose, 10 lbs.; dextrine, 10 lbs.; glycerine, 10 lbs.; tartaric acid, 5 lbs.; gum guiac, 5 lbs.; gum amber, 3 lbs.; gum tragacanth, 3 Lbs.; aniline red, 1 lb.; aniline oil, 1 lb.; crude anthracene, 5 lbs.; petroleum pitch, 10 lbs.; albumen from eggs, 2 lbs.; tar from passing chlorine through aniline oil, 2 lbs.; citric acid, 5 lbs.; sawdust of boxwood, 3 lbs.; starch, 5 lbs.; shellac, 3 lbs.; gum Arabic, 5 lbs.; castor oil, 5 lbs."
The so-called aniline colours are not all derived from aniline, such colouring matters being in some cases derived from other coal-tar products, such as benzene and toluene, phenol, naphthalene, and anthracene, and it is remarkable that although the earlier dyes were produced from the lighter and more easily distilled products of coal-tar, yet now some of the heaviest and most stubborn of the distillates are brought under requisition for colouring matters, those which not many years ago were regarded as fit only to be used as lubricants or to be regarded as waste.
The 12 gallons of tar yield 1-1/10 lb. of benzene, 9/10 lb. of toluene, 1-1/2 lb. of carbolic acid, between 1/10 and 2/10 lb. of xylene, 6-1/2 lb. of naphthalene, and 1/2 lb. of anthracene, whilst the quantity of pitch left behind is 69-1/2 lb.
Besides directly attacking the production of raw materials and intermediates, the Germans used an indirect method which has been described as "full line forcing." They were the sole producers of certain specialities, such as alizarine colours, anthracene colours, and synthetic indigo.
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