The Colors of Coal Tar. Number II.

Scientific American 20, 17.5.1862

The art of dyeing various colors with one principal coloring substance and different reagents, has long been known and practiced in all countries. Thus with cochineal and lac insects, scarlet, red, purple and lilac colors can be dyed by using different reagents, principally metallic salts such as the bichloride of tin, oxides of iron, &c. With madder - a vegetable substance - red, purple, and lilac colors are also dyed by employing such reagents as alum and the acetate of iron. Applying the same well known principles of color chemistry to aniline colors great success has already been obtained. It is indeed one of the most remarkable facts connected with modern chemistry, that, although it is but a very few years since colors have been produced from the products of coal tar, a far greater varieety has already been obtained than from any other chief coloring agent. Thus from Perkin's aniline purple, described in our last article on this subject, a blue dye can be made by boiling the insoluble purple for some time in hydrochloric acid diluted at the rate of 10 parts of commercial acid to 100 parts of water.

Aniline Red Dyes. - The beautiful crimson color now called magenta, was produced by Dr. Hoffman in September, 1858, and an account of it was then transmitted to the Academy of Sciences. He called it carbo-triphenyl-triamine, a crystalline base formed by the condensation of three molecules of aniline reunited by carbon substituted for hydrogen. It was M. Verguin, of France, however, who first produced this beautiful color in merchantable quantities for dyers, and his mode of preparation was first patented in Europe April, 1859, by MM. Reynard Brothers, in Lyons, France. It is usually prepared as follows: - Into a glazed iron pan 100 parts of aniline and 60 of anhydrous bichloride of tin are placed, and the whole heated to about 392° for about twenty minutes. This produces a dark liquid, which becomes thick and glutinous when it cools. It is then mixed with boiling water and filtered, and to this filtrate is added common salt which precipitates the color called fuchsine. M. Joseph Renard obtained an American patent July 31, 1860, from which the following is an extract: - The preparation of the coloring matter referred to is based upon the discover that if aniline be heated to a temperature of from 380° to 400° Fah., together with several anhydrous or desiccated compounds, the mixture thus produced will be changed into a substance of such dark color that it appears to be almost black, but which, when applied in layers or diluted, is transparend and of a beautiful red color. The substances or chemical compounds by the treatment of which aniline produces the red coloring matter are quite numerous, but may be classified under the following groups: -
Sulphates of peroxide of iron.
Nitrates of protoxide of mercury.
Chlorates of protoxide of tin.
Bromates of binoxide of mercury.
Iodates of binoxide of tin.

All ferric, mercuric, stannic and uranic compunds, the yellow oxide of uranum, the oxide, chloride, bromide, iodide and fluoride of silver. Many of these compounds being too rare or expensive for practical purposes, M. Renard therefore confines himself to the use of the following: -
Bichloride of tin.
Bichloride of Mercury.
Protosulphate of mercury.
Photonitrate of mercury.
Deutonitrate of mercury.
Sulphate of tin.
Nitrate of peroxide of iron.
The following is the claim of the patent: -
I claim combining with aniline the metallic salts specified, or their equivalents, and treatin gthe same in such a manner as to produce a red in contradistinction to a purple or bluish coloring matter or dye.

Magenta has also been made with the permanganate of potash and the binoxide of lead, and with arsenic acid, as described by Dr. Crace Calvert. Two parts of aniline and one of arsenic acid are heated to about 250°, and when the color becomes red boiling water is added, and the product allowed to cool; common salt is then added, which precipitated the coloring matter, and this is then washed and dissolved in methylated alcohol. This substance is a powerful organic base slightly soluble in water. When solid it is a brittle mass having a beautiful green metallic luster.

Commercial purple and red aniline colors differ in their composition as follows: - Purple, C₃₆H₁₇N₃O₂. Red C₃₆H₂₀F₄O₄. The fuchsine, red, dissolves in ammonia and in sulphuric acid, and is discolored with the acid, but the purple is unaffected with these reagents. Silk and wool are dyed with fuchsine by simply adding some of the color to a slightly acidulated bath of water. Its dyeing power is so great that ten grains of it will color two square yards of silk. This beautiful red color of aniline has been called azeleine fuchsine, roseine, magenta, &c. Dr. Hoffman proposed the appropriate name rosaniline for it, as magenta and solferino are flash tems which should be repudiated.