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DYEING AND CALICO PRINTING.

proportion, according to the shade required. The more aniline is added themore hydrogen is replaced, and the more the violet produced inclines to ablue. The aniline employed should be as pure as possible. About equalweights of magenta and aniline are employed, according to the original speci-fication of Girard and De Laire. The retort is raised to a temperature of165° to 190° C., and maintained there till the process is complete, which maybe in 60 to 90 minutes. The progress of the operation is observed by meansof a rod inserted at an aperture arranged for the purpose. A drop of the con-tents being thus withdrawn is placed upon a white porcelain plate, mixed witha little alcohol and acetic acid, and its colour examined. The reddershade of violet is a mono-phenyl rosaniline, whilst the blue shade is diphenyl-rosaniline.

The process is varied slightly by different manufacturers. Levinstein mixes3 parts of aniline with 1 of magenta, and maintains the whole for three orfour hours at 180° C. A reddish shade is yielded by roo parts magenta, 100parts aniline, and 25 parts acetate of soda. As soon as the desired shade isobtained the contents of the retort are run out and heated with very dilutehydrochloric acid, which dissolves out any unconverted aniline that remainsin the mixture. The violet colour is left floating on the surface of theliquid. It is strained off, freed from traces of acid by washing with water,dried, and powdered. The red-violet very much resembles solid magenta inappearance, but is less green. The bluer the violet the more of a coppery-redis its reflection. In the production of the very bluest violets soap is oftenemployed. A favourite mixture is 100 parts aniline, 300 magenta,75 acetate of soda, and 66 of a good curd soap. Prolonged heating, evenwith one and the same mixture, gives the result a bluer tone. The yield isgreater than the weight of the magenta employed.

These violets are insoluble in water, either hot or cold. They dissolve inalcohol, wood-spirit, aceton, acetic acid, and concentrated glycerine. Theuse of these violets has very much diminished since the methylated andethylated substitution-produCts of rosaniline—the so-called Hofmann andParis violets—were discovered.

Of the Hofmann violets, chiefly manufactured by Messrs. Brooke, Simpson,and Spiller, there are a variety of shades, ranging from the reddest (R.R.R.) tothe bluest (B.B.B.). These marks correspond to certain different gradesof substitution, ethyl or methyl here taking the place of hydrogen, in therosaniline atom for atom. The shade R.R.R. consists chiefly of mono-methylated rosaniline, whilst B.B.B. is almost exclusively composed of tri-methylated. The apparatus employed on the Continent in the manufactureof these colours is represented in Fig. 18. It is a boiler of enamelled iron,made strong enough to bear a pressure of 20 to 25 atmospheres, and varyingin capacity from 80 to 100 litres. It may be heated either on the water-bathprinciple or by means of a steam-jacket. It is fitted up with a thermometerand a pressure-gauge.

For a red violet, “ R.R.R,,” the materials are—

Rosaniline. 10 kilos.

Alcohol.100 litres.

Iodide of methyl or ethyl. 8 kilos.

Hydrate of potassa or soda. 10 ,,