Manufacturer and builder 5, 1870
If to a resinous solution an aniline color is added which is soluble in the same, it will of course be colored red; but when the solution is evaporated, the remnant will wither discolor the aniline entirely or give it a violet tinge, which is especially the case if a solution of common resin in alcohol has been used. If, however, a solution of shellac in alcohol is employed the remnant of the evaporation becomes beautifully blue. The product this obtained will be insoluble in ether, but soluble in alcohol and acetic acid, with a beautiful blue color. If in place of a solution in alcohol, an alkaline solution of shellac is used, and for some time boiled with red aniline, the so-called "bleu de Mulhouse", which was discovered as early as 1861 by Shaeffer and Gros Renaud, is obtained. The solutions of this blue in alcohol or acetic acid are discolored by ammonia, and turn reddish-brown by the addition of potash; but by adding a quantity of acid sufficient to neutralize the alkali, (the ammonia or the potash,) the color is restored; while an excess of acid, in case it is sulphuric, nitric, or hydro-chloric, destroys the color again. By the addition of water to the alcoholic solution, the blue color is precipitated. This color is, however, not permanent, and appears to change by the influence of air and moisture; at least, after some time it does not possess the same solubility as before. The so-called Perkins violet, the mauve-aniline, shows the same results as the Fuchsia, but the coralline acts slightly different.
The above-described action is only produced when using the shellac; and as even a very small quantity of the same is sufficient to produce the blue color, the reaction may be used as a test to recognize aniline red. But what is of more importance, aniline red may in turn be used to detect the presence of shellac in a mixture, or rather solution, of different resins.