DYEING AND CALICO PRINTING.

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Refined Blues are obtained by various'methods. The crude produdt is mixedwith alcohol, and poured in thin streams into water acidulated with hydro-chloric acid. There is formed a salt of aniline, which remains in solutionalong with any excess of unconverted rosaniline, and the blue is precipitated.It is then colleded on a filter, and repeatedly washed with boiling acidulatedwater.

Night blue, so called because it preserves its tone by artificial light, issimply a salt of triphenylic rosaniline, perfedtly pure. To prepare it, therefined blue resulting from the last operation is repeatedly washed with coldalcohol, and then dissolved in boiling alcohol, after having been finely

Fig. ig.

Apparatus for the Preparation of Aniline Blue.a. Retort of enamelled cast-iron, immersed in the oil-bath, b. c. Vertical shaft,carrying two agitators, the one d , a spiral, and the other fitted with wings parallelto the sides of the retort, and with teeth extending very nearly to the bottom.

/. Cover fitted on to the retort by the pressure-screws, g, and carrying h, a stuffing-box for the shaft c; another, t, for the thermometer and a tubulurej', communicatingat will by means of cocks with a worm, k, or a worm cohobator, k', and l, a tube forintroducing steam into the apparatus. The steam may be otherwise introduced byhaving a hollow shaft for the agitator in place of a solid one. Movement is givenby the pullies, m m, and the cog-wheels, n 11.

powdered. The mixture is then filtered, and mixed with an alcoholic solutionof caustic soda, when the blue is entirely thrown down as a base. When thewhole is cold the colour is collected on a filter, washed repeatedly with boilingwater, and then treated with a sufficient quantity of the acid intended to forma salt.

Another method is to dissolve the refined blue, in a mixture of alcohol andhydrochloric acid, in double-bottomed retorts enamelled within. The mixtureis boiled, when a part of the alcohol distils off, and it is then allowed to cool.

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