ANILINE REDS.
181
The liquid is run, through large filters of woollen cloth, into large sheet-ironreservoirs, holding 8 to 10 cubic metres each, and so arranged that their con-tents can be heated by currents of steam. The filtrate, which no longercontains any matters insoluble in water, consists of solution of hydrochlorate,arsenite, and arseniate of rosaniline, along with free arsenious and arsenicacids. It is now necessary to eliminate the arsenic. For this purpose, andfor every 200 kilos, of raw colour, 240 kilos, of common salt are added to theliquid in small quantities at a time. The decomposition is accelerated byblowing in steam, the final result being hydrochlorate of rosaniline, and, onthe other hand, arsenite and arseniate of soda. The rosaniline compound,being insoluble in strong saline solutions, separates out and rises to thesurface. The liquid is cooled, the colour collected, and, after a few days, themother-liquor is run into large tanks, where it deposits the small amount ofcolouring matter still held in suspension.
The colour thus obtained is washed with boiling water, in small quantities,to remove the chloride of sodium and the bulk of the arsenical salts whichit still retains.
If a higher degree of purity is required, it is re-dissolved in boiling water,filtered, and allowed to crystallise.
There is a method of effecting the solution of the crude aniline red underpressure. This procedure saves time and labour, lessens the quantity of wateremployed, giving consequently a more saturated solution, and abridging thefiltrations. The apparatus is represented in Fig. 17.
The colour thus obtained is the hydrochlorate of rosaniline, a base havingthe composition C 20 Hi 9 N3,H 2 0. This base, when uncombined, pure andcrystalline, appears in the form of small tables or needles, which if preservedfrom the attion of the air are colourless, but redden rapidly on exposure. Itpasses from a colourless state to a rose, or even red condition, on fusion,without any change of composition. It is inodorous in the cold, but whenheated gives off a scent of diphenylamine. Its taste is rather bitter. Itsspecific gravity is i*8. It melts in boiling water, and is decomposed at 220 0 C.If kept for ten hours, or upwards, at the temperature of 210° to 220° C., it isgradually transformed into a violet colouring matter, insoluble in water, andbut sparingly soluble in acetic acid and boiling alcohol. Rosaniline dissolvesm boiling water to the extent of 2 or 3 grammes per litre, and is chiefly re-deposited as the liquid cools. A litre of ammonia dissolves 4 grammes. Insoda and potash lyes it is soluble to about the same extent. Lime-waterdissolves 3 grammes, and baryta-water rather more. In alcohol it dissolvesto the extent of 10 grammes per litre. Wood-spirit, acetone, carbolic acid,and aniline dissolve it freely; the latter in all proportions. On the otherhand, it is insoluble in ether, benzol and its homologues, and bisulphide ofcarbon. It is soluble in almost all acids, mineral and organic, forming well-defined salts, which crystallise with great facility.
Rosaniline is a powerful base, displacing ammonia from its combinationswith acids at xoo° C. The coloured solutions of rosaniline and of its saltsare completely decolourised by caustic and carbonated alkalies, but the colouris restored by the addition of a sufficient quantity of an organic acid. Proto-chloride of tin decolourises them at ordinary temperatures. Free chlorinehrst changes the colour to blue, and then destroys it. Chloride of lime rapidly