Coal-tar Colours





Our work might be considered incomplete without some allusion to the

coal-tar colours, even though they are rather dyes than pigments, not

possessing sufficient stability for the palette. To avoid repeated

reference, we have preferred grouping them in this chapter, irrespective

of hue. Consequently, yellow, red, blue, orange, green, purple, brown,

and black, will be all comprised under the heading of coal-tar colours.



Previous to the year 1856 the colouring matters derived from coal-tar

were practically unknown. Until then, that black evil-smelling substance

was looked upon as almost worthless; but gradually the unsightly grub

emerged into a beautiful butterfly, clothed first in mauve and next in

magenta. After its long winter of neglect, there sprung from coal-tar

the most vivid and varied hues, like flowers from the earth at spring.

At a touch of the fairy wand of science, the waste land became a garden

of tropic tints, and colour succeeded colour, until the whole gamut had

been gone through. Never was transformation more dazzling or more

complete. The once despised refuse was now a valued commercial

product--indeed a trade in itself. Perfectly fascinated by the study,

chemists threw themselves heart and soul into coal-tar, and coal-tar

colours were to be seen everywhere.



It were beside our purpose to enter into the various stages through

which coal has to pass to become colour. Enough to state that to the

introduction of gas-light we are indebted for the acquisition of

coal-tar colours, the starting point for the production of mauve,

magenta, &c., being the manufacture of coal-gas. From the destructive

distillation of coal, coal-tar oil results; and from this are obtained

the products which yield the colours in question. Among these products

may be mentioned aniline, rosaniline, napthaline, chinoline, carbolic

acid, picric acid, &c., with their derivatives.



Of the fifty-one compounds furnished by the distillation of coal,

perhaps the most popularly associated with coal-tar colours is aniline,

to which we will therefore confine ourselves. Discovered in 1826, this





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