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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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