Bleu de Paris is prepared by heating 9 parts by weight of bichloride of tin and 16 parts of aniline to a temperature of about 350° F., in a sealed tube, for 30 hours, when a blue product is obtained, which is soluble in alcohol, and crystallizes therefrom in fine needles of a lively blue color. Bleu de Paris is soluble in water, alcohol, wood spirit, and acetic acid, and insoluble in ether and bisulphuret of carbon.
Aniline Green or Emeraldine is obtained by acting upon a hydrochloric acid solution of aniline by chlorate of potash, when the aniline oxidiied/ and yields a dull green precipitate, which, on drying, becomes an olive-green residue. It is insoluble in water, alcohol, ether, and benzole, and in the presence of a free acid the green color improves in appearance, though it returns to its original shade when the free acid is removed.
Quinoline or Chinoline is present in coal-tar, and may be employed to yield three coloring matters—a violet, a blue, and a green; but the processes as yet followed in their preparation belong more to the laboratory experiments of the scientific chemist than to the practical operations of the manufacturer.
Picric Acid is obtained by acting upon many organic substances, such as indigo, ani line, carbolic acid, salicin, silk, aloes, gum-resins, etc., by nitric acid. On the com mercial scale, carbolic acid is generally employed, and it is first treated with nitric acid of slightly less density than 1300 (water = 1000), and afterwards boiled with stronger acid, when it passes into picric acid, and is precipitated on dilution with water. It can be purified by recrystallization from boiling water. Pure picric acid crystallizes in lamina of a primrose yellow color.
Azuline is the only other coloring matter of practical importance derived directly or indirectly from coal-tar. It is a brittle, non-crystallizable substance, with a copper colored metallic appearance. It is sparingly soluble in water, but is soluble in alcohol, yielding a fine blue solution with a shade of red. Treated with concentrated sulphuric acid, it becomes a fine blood-red liquid, which, on dilution with much water, gives a red precipitate of azuline.
Pittacal is a blue coloring matter obtained from coal-tar.
Dyeing of Silk and Wool by the Coal-tar department of the operations of the dyer is very simple, as the silk and wool fibers possess the power of taking up and fixing the majority of these coloring matters with great rapidity, whenever the yarn or textile fabric is placed in the vessel containing a solution of the color. In the dyeing of silk with aniline purple, violine, and roseme, the alcoholic solution of the color is diluted with 8 times its volume of hot water acidulated with tartaric acid, and thereafter treated with a larger quantity of cold water. The silk is merely worked in this compara
tively weak solution of the dye till the shade of color is deep enough. The addition of a little sulphate of indig to the dye-vat assists in bringing out a more decided blue tint. The same result is obtained by first dyeing the goods with Prussian blue before immer sion in the coal-tar color. When silk is to be dyed with fuchsine. picric acid, chinoline blue or chinoline violet, the goods require only to be worked in water-solutions of these colors. A little acetic acid added to the vat containing the fuchsine or picric acid is advantageous, and if a solution of sulphate of indigo is mixed with the solution of picric acid, the goods acquire a fine green color.
Azuline is attached to silk with more difficulty than any of the preceding colors. The silk requires to be worked first in a solution of azuline acidulated with sul phuric acid, and thereafter the liquid is raised to the boiling-point, and the silk con tinued to be worked in it. The goods are then washed in water, worked in a bath of soap-lather, rinsed, and finished in a weak acid bath.
Wool is dyed with aniline purple, violine, roseine, fuchsine, and chinoline by merely working the yarn or cloth in a vat containing a water-solution of the coloring matter at a temperature ranging between 112' and 140' F.
Cotton has not the power of firmly attaching, directly, coal-tar colors to its fiber so as to resist the action of soda and of soap, When the cotton, however, is treated with a solution containing much tannin, such as a decoction of sumach, or galls, for an hour or so, then introduced into a dilute solution of alum or stannate of soda, and, lastly, passed into a dilute acid liquid, and washed in water, it acquires a great power of firmly attaching aniline purple, roseine, violine, fuchsine, and chinoline colors, whenever it is worked in a dye-vat containing these coloring matters. This principle of the attach ment of these colors to cotton by means of a mordant of tannin and alum, may be applied in printing patterns upon cloth, as in calico-printing (q.v.). The pattern is printed on the cloth by means of tannin and alum dissolved in water, and thickened with gum; and afterwards, when the prepared goods have been introduced into a hot dilute acid solution of the coloring matter, the dye becomes attached to those parts on which only the tannin has been printed, and leaves the other parts uncolored. Another mode is to mix the dye with albumen or lacterine, print on the cloth, and then subject to the action of steam, which coagulates the albumen or lacterine, and at the same time fixes the color on the cloth.