Substitutes for Indigo.

Scientific American 20, 16.11.1861

Owing to the scarcity and high prices of indigo and the great demand for dying fast blue woolen cloth and flannel, a cotemporary states that the woolen dyers in Hampden county, Mass., are buying up carrot tops from the farmers, paying at the rate of twelve to fifteen dollars per acre, and using them for dying blue. Carrot tops yield a species of indigo, the same as woad, and they are used in what is called the "pastel-vat." The color obtained from them is as durable, we think, as that of indigo, but it requires a great quantity of them to yield a small amount of coloring matter.

It appears to us that chemists will find what are called "the refuse products of petroleum oils," good subjects for experiments to obtain a rich coloring substitute for indigo. Scarlet, red, crimson, drab, green and blue colors have been obtained from compounds of aniline, but these are not fast colors. What is wanted is some discovery to render aniline blue a permanent color, and when it is well known that, according to Dumas, a radical salt of indigo is anyle, which is composed of C₁₆H₅N, the manufacture of indigo from coal tar is not a hypothetical proposition.