For example, aniline is contained in coal-tar, but if we depended on the aniline contained ready made in coal-tar for our aniline dyes, the prices of these dyes would place them beyond our reach, would place them amongst diamonds and precious stones in rarity and cost, so difficult is it to extract the small quantity of aniline from coal-tar.  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 is shown very clearly in the following table (Table A).

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.  But our table shows us more; it indicates to us what the steps are from each raw material to each colouring matter, as well as showing us each colouring matter.  We see here that our benzene yields us an equal weight of aniline, and the toluene (9/10 lb.) about 3/4 lb. of toluidine, the mixture giving, on oxidation, between 1/2 and 3/4 lb of Magenta.  From carbolic acid are obtained both Aurin and picric acid, and here is the actual quantity of Aurin obtainable (1-1/4 lb.).  From naphthalene, either naphthylamine (a body like aniline) or naphthol (resembling phenol) may be prepared.  The amounts obtainable you see in the table.  There are two varieties of naphthol, called alpha- and beta-naphthol, but only one phenol, namely, carbolic acid.  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.  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.  Chemically pure Alizarin crystallises in bright-red needles; it is the colouring principle of madder, and also of Alizarin paste.  But the most wonderful thing about substantive coal-tar colours is their immense tinctorial power, i.e. the very little quantity of each required compared with the immense superficies of cloth it will dye to a full shade.

TABLE A.[2]

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