BLUE COLOURING MATTERS. PHENYL-ROBANILINE8.—When a rosaniline salt i8 heated with aniline, hydrogen is replaced hy phenyl, and ammonia is given off, producing monophenyl-, diphenyl-, and triphenyl-roaaniline ; the salts of the first have a reddish-violet colour ; those of the second, bluish-violet ; and those of the third, a pure blue colour, and are known as " candle blue " or " night blue,'' since their colour is unaltered by artificial light. For the inanufacture of aniline blue, the purer the aniline itself, the better will be the colour of the dye produced. The aniline which passes over in the preparation of magenta is generally used for the better kinds of blue, on account of its freedom from the higher homologue bases. Commercial anilines may be fractionized, and the product coming over at 182°-185° (360°-365° F.), may be retained for the preparation of the finest blues.
These blues are more readily formed when weak organic acids, ouch as acetic, benzoic, &c., are present ; in their dyeing qualities, much ia gained by selecting an aniline of low boiling-point. The proportions of the ingre,dients vary ; but, aa a rule, free auiline is used in large excess. On the Con tinent, they are prepared in a series of enamelled cast-iron pots, heated in an oil bath over a furnace. The covers are secured by clamps, and supplied with a small opening for withdrawing samplea, and a bent tube for leading away vapours to a condenser. Sometimea these tubes are inclined so that the condensed vapours are returned. If the heating is carefully conducted, the volatilized aniline should be trifling. Each pot is provided with au agitator, and has a capacity of about 20 lit. When starting, they are half-filled with the materials, and the covers with their appendages are fitted on, and secured. The covers, tubes, and stirrers are best arranged so that they hoist out together when the pots are opened. A thermometer is placed in the oil bath. A charge may be about 5 kilo. rosaniliue salt (acetate, or hydrochlorate), and 10 kilo. aniline ; the temperature of the bath should be kept between 190° (374° F.) max., and 165° (329° F.) min.; the aniline must not boil. The operation lasts about two hours. The free aniline is recovered by distilling with a current of
ateam, or removed hy meana of an acid, or the colouring matter is taken up by alcohol or wood spirit, In this country, a small magenta-still ia used instead of the series of pots.
By the subsequent purification of the crude product, the following colours are obtained:— Direct Blue.—This is the crude colour deprived of the free aniline by a current of steam, or by washing with weak hydrochloric acid, in enamelled iron pana ; the acid poured off one is added to the next, and so on. The aniline is recovered by distillation With lime.
Purified Blue.—The product in the still is liquefied with wood-spirit, and allowed to trickle into dilute hydrochloric acid. The free bases are taken up, and the colouring matter falls to the bottom ; it is oollected on flannel trays, and well washed with acidulated boiling water.
Night Blue.—So called from the absence of violet when viewed by gas or candle light. The crude product is well washed with wood-spirit, and sometimes boiled after being well divided. It is easier and cheaper in all cases to work upon the previously purified product for the next purifi cation. Percolation with alcohol or wood-naphtha will purify the " direct blue" to any required degree, after the heavy anilines have been removed by hydrochloric acid.
By varying the proportion of materials and farther purifying, the following different qualities of tl tete blues are obtained :— B Blue.—This blue is obtained by heating for two hours, at 180° (356° F.), a mixture of 2000 grms. pure rosaniline, 3000 grms. aniline; distilling at 182°485° (360°-365° F.); and adding 270 grma. glacial acetic, or benzoic, acid. The products from benzoic acid are always more tinted with green than those from acetic acid ; the former are uaed for silk, the latter for wool. The ooldur may be made purer by pouring it gently into an enamelled iron pot containing 10 kilo. hydrochloric acid, with brisk and continuous stirring. The precipitate is filtered, and well washed with boiling water acidulated with hydrochloric acid, till it is reduced entirely to powder ; the yield is about 3500 grms.