200

DYEING AND CALICO PRINTING.

rosaniline, analogous to the sulphindigotic. In the preparation of the earliersoluble blues a very large proportion' of sulphuric acid was employed. The

mixture was—

Sulphate of triphenylic rosaniline. io parts.

Sulphuric acid.40 ,,

The ingredients are mixed at once, and the rea&ion accelerated by means ofheat. The temperature is raised, by means of a steam-jacket, to 130° or 140*C., but must never pass 150°. When the mass is homogeneous, and when adrop of the acid blue gives a complete and clear solution in ammonia, thereaction is over. The mass is allowed to cool, and poured by slow degreesinto 8 to 10 times its weight of water, with constant stirring. The blueis thrown down in a state of fine division, which is filtered and washed till thewater begins to take a blue colour, showing that the mass is no longer acid,the coupled blue sulpho-acid being insoluble in dilute acids, though soluble inpure water. It is then dried in any convenient manner. When dry it is putin a cast-iron vessel enamelled within, mixed with a slight excess of ammonia,and heated. The coloured salt floats on the surface as a golden-bronzy layer.It is collected, broken up, dried, and powdered, and is now ready for use.The more recent method of preparing soluble blues differs in employing asmaller proportion of sulphuric acid, and in keeping the temperature belowioo° C. One kilo, of B.B. blue is finely powdered, and added by degrees to3 litres of concentrated sulphuric acid, and the mixture is kept at the tem-perature of the water-bath till a drop thrown into water gives a blue precipitate,which is washed by decantation. The precipitate thus purified and freed fromacid should not colour water, and should dissolve without residue in aqueoussolutions of soda or ammonia. The whole mass is then poured into 30 litresof water, constantly stirring,—an operation performed in wooden vats hoopedwith wood. The whole is allowed to settle for twenty-four hours, and is filteredthrough stout flannel. The precipitate, when it ceases to drop, is pressed.The pressed residue is heated in the water-bath with hydrate of soda till allthe mass is dissolved. The neutralisation of the soda should be as exadt aspossible. The blue is then allowed to dry on enamelled plates, in a hotchamber, powdered, and mixed with 20 per cent of crystalline carbonate ofsoda.

Nicholson blue and Guernsey blue are manufactured by Messrs. Brooke,Simpson, and Spiller, and have the advantage of ready solubility in water,combined with a greater degree of fastness than most aniline colours canoffer. The exact method of their preparation has not been made public.

In dissolving and dyeing with aniline blues, a variety of processes areemployed. The ordinary blues, as we have already intimated, are insoluble inwater, and can be brought into solution by the use of alcohol or wood-spirit.*The purer a blue, the more alcohol is required for its solution, and the greaterdifficulty is experienced in fixing it upon cotton. The common blues areprepared for use by boiling in alcohol sufficient to take them up, and then verycarefully straining. They dye wool and silk without mordants, the former at

* It may be useful to point out a distinction often overlooked. Methylated spirit is commonalcohol mixed with a small percentage of wood-spirit, which latter is otherwise known asmethylic alcohol or wood-naphtha.