Colors from Coal Tar.

Scientific American 12, 17.3.1866

Aniline, or coal tar colors, have now been extended in number , so that all the colors of the rainbow, and all the shades, can be obtained from coal tar. Aniline was discovered by Unverdorben in 1826, who procured it by the destructive distillation of indigo. It is now obtained in small quantities directly from the destructive distillation of coal, as in gas-works, but is generally manufactured from the lighter coal tar naphtha. When the naphtha is rectified, the portion which distils over at a temperature of 180° Fah. is benzole, and this substance was discovered by Faraday in 1825. By the action of strong nitric acid, the benzole is converted into nitri-benzole, and this latter, when agitated with water, acetic acid, and iron filings, becomes aniline. By the action of oxidizing agents, such as chloride of lime,bichromate of potash, chrloride of mercury, etc., the aniline, which is colorless by itself, can be transformed into all shades of violet, mauve, magenta etc. By the researches of Hofmann, the number and beauty of the aniline colors have been increased. While numberless shades of reds and purples can be obtained, there is a splendid green, called verdine, discovered by Eusebe, and which remains true, pure green even by candle or gaslight; a blue which is as clear as opal, a good yellow and a fair black. In short, dyes of all hues can be obtained from aniline, which in its turn, is procured from the coal tar. The intensity of these aniline colors may be indicated by the fact that one grain of magenta in a million of water gives a good red; one grain in ten millions of water exhibits a rose pink; one grain in twenty million communicates a blush to the water; and one grain in fifty million tinges the water with a reddish glow. The powerful tinctorial virtues of these dyes may be learned from a circumstance which occured during the passage of the Great Eastern between Liverpool and New York, when the sea was observed to exhibit a crimson hue for some distance around the vessel, and when it was afterwards discovered that the bloody sea owed its color to a wave having stove in a plate of the Great Eastern, and thus the water got access to certain vessels which contained magenta.

- Mining Journal.

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