Solvents for Indigo.
DR. E. JACOBSEN.
Translated by C. Dengenhardt.
Some new solvents for indigo have lately been given by de Aguiar and Baeyer, and by Prof. Wartha. (See American Chemist, Vol. I, p. 472). To these I will also add a few which I have discovered. That aniline will dissolve indigo has been known several years, from my own experiments. But an equally good solvent for indigo is nitrobenzol, which when heated with indigo is colored a deep violet blue, and on cooling deposits flaky crystals and then appears dark red, probably from red indigo.
In greater or less quantities the following substances dissolve indigo at their boiling points:
Castor oil, acetone, hydrate of chloral, camphor, oil of turpentine, balsam of copaiba, cedar oil (oil of Juniper virgin), amylic alcohol, oil of lavender, white beeswax, Japanese vegetable wax and Carnauba wax, (from this last small flaky crystals precipitate).
The higher the boiling point of the solvent, the redder is the appearance of the solution, so that bodies like acetone, amylic alcohol and hydrate of chloral give a clear blue. Castor oil, cedar oil, etc., a violet blue, and the different kinds of wax a purple red solution. If kept for a short time at the boiling point with white wax, the color changes from scarlet to orange, and at last to a brown. The indigo is reduced by the formation of acrolein, and the solution retains its brown color even on the addition of gasoline.
If powdered indigo is added to melting picric acid, the former will be decomposed with deflagration.