The mother-liquor from a previous crystallization is generally used for dissolving the crude rosaniline after the separation of the humus ; a crop of crude crystals is obtained, and the motherliquor, which still holds much colouring matter in solution, is treated with milk of lime, to remove the arsenious and arsenic acids, so as to avoid the dangers of poisonous salts. Any colouring matter carried down with the brae is taken up by acetic acid. English rosaniline, made in this way, unless carefully crystallized, contains a little arseniate, which accounts for the bad effects produced on the skin by articles dyed with the impure salt. This fact proved very prejudicial to aniline dyes, especially for hose, few years ago. and ought not to be overlooked by the manufacturers of tar colours. The advantages of this method are absence of acid fumes during the boiling, portability of salt as compared with hydrochloric acid, and economy of cost.
The method most extensively adopted is to boil the crude magenta for several hours, with a large excess of lime, under pressure in an ordinary steam boiler, with perforated ag,itating fans closely arranged, so as to thoroughly break up the melt ; any unaltered aniline is thus carried away and condensed, the lime is converted into arsenite or arseniate (insoluble salts), and the rosaniline 'is obtained free by filteriog whilst boiling hot. On cooling, a crop of impure crystals is deposited, the mother-liquor is repeatedly concentrated for fresh crops, or is used for boiling with fresh melt. It is better to exhaust the lime residues by boiling and washing than to extract the remaioing rosaniline by acids, as is frequently done. Wilson and Cant digeat the crude base with commercial benzol, which takes up the resinous or gummy matters—chrysaniline and chrysotolui dine ; these are recovered by driving off the benzol, and, after purification in the usual way, are sold as "phosphine." The rosaniline is converted into hydrochlorate by the addition of acid ; an excess precipitates the salt for the finer class of dyes ; it is washed with solution of common salt, and recrystallized ; by repeatiog the operation, different qualities of dye 9,re obtained.
Treatm,ent of Magenta Residues.—In the ordinary manufacture of rosaniline, chrysotoluidine, mauvaniline, and violaniline are simultaneously formed ; the separation of these not only enables a manufacturer to enhance the beauty of his reds, but by their separation and purification, he obtains a great variety of colouring matters, at comparatively little expense. The separation of these bases
depends upon their solubilities in the menstrua employed. In boiling hydrochloric acid, diluted with 2i times its bulk of water, rosaniline is nearly insoluble, while the other bases are readily soluble ; on cooling, mauvaniline, and a little rosaniline, separate out as hydrochlorates. Chryso toluidine is soluble in an aeid solution of common salt, from which mauvaniline and rosaniline are precipitated. By neutralizing this solution with soda, chrysotoluidine precipitates (or violaniline) may be separated from chrysotoluidine and mauvaniline ; by dissolving these bases in aniline, and just saturating with hydrochloric or acetic acid, the violaniline is precipitated ; the filtrate is diluted, and mixed with common salt, by which mauvaniline is thrown down ; caustic soda in excess preci pitates chrysotoluidine, and the aniline is recovered by distillation.
Girard and De Laire proceed thus :—On boiling 1000 kilo. with 12,000 kilo. water, and 500 kilo. ordinary hydrochloric acid, the violaniline is taken up ; 125 kilo. of the same acid is added to the boiling filtrate, which, on cooling, deposits hydrochlorate mauvaniline, with a little rosaniline and resinous matter ; 625 kilo. common salt added to this filti ate throws down a little mauvaniline, and rosaniline salts ; the mother-liquor, treated with 83 kilo. carbonate soda, soon deposits salts of rosaniline, and a little chrysotoluidine ; the further addition of 37i kilo. carbonate gives a precipitate consisting almost entirely of chrysotoluidine ; in this way, 5-10 per cent. of colouring matter may be recovered from the waste of the crude rosaniline. The separation is more easy and economical if all the rosaniline be extracted by boiling, as for the crude article. The further treat ment of these matters with acid, common salt, and carbonate of soda, will yield different colouring matters, which will he noted in their proper places. See Rosaniline, Violet, Yellow, and Brown.
Letwaniline. C201-12,Na.—On boiling an acid solution of rosaniline with zinc, or mixing it vvith ammonium sulphide, it gradually becomes colourless, and a yellow resinous substance is deposited. This is crushed, washed with water, and dissolved in weak hydrochloric acid ; the addition of strong acid precipitates the hydrochlorate of this base. Ammonia, added to a solution of this salt, yields the pure base, which is a white powder, easily soluble in alcohol. By oxidation, it yields brown colouring matters (q. v.).