ANILINE BLUES .

197

solution of a salt of aniline and alcohol, and adding to this another solutioncontaining chlorate of potassa and hydrochloric acid : after a short time adark indigo-blue precipitate is produced, which, when washed with water, maybe dried and preserved. This colour is not pra&ically available for dyeing,owing to its insolubility. Dr. Hofmann also produced this colour by adtingon a solution of hydrochlorate of aniline with a solution of hypochloric acid.Messrs. Clift, Lowe, and Calvert, of Manchester, also produced it by adtingon hydrochlorate of aniline with chlorate of potassa. M. Willm has alsoobtained this peculiar blue by mixing the sesquichloride of iron with nitrateof aniline : after a short time a chemical adtion sets in, when the liquorbecomes purple, from which is gradually deposited the blue colouring matter.The same readtion is obtained by substituting bichromate of potassa for thechloride of iron. According to this same author, this blue is also procuredwhen a salt of aniline is mixed with red prussiate of potassa, but the blueproduced in this instance is soluble in alcohol, which is not the case with theother varieties. These blues resist all chemical agents excepting acids, whichturn them green. This is the only drawback to their employment as substi-tutes for indigo, but notwithstanding this defedt they are applied in calico-printing for producing greens, blues similar to indigo, and blues and greens sodark as to appear black.

Some of the most important aniline blues are made by phenylation, in amanner similar to what has been already described under aniline violets.The apparatus employed is a retort of enamelled cast-iron, of the capacity ofabout 20 litres, and heated by means of a paraffin-bath. It is composed oftwo pieces, the neck and the cylinder, united by means of pressure-screws.To the neck of the retort are adapted a receiver and a cohobator, the latterserving to maintain the same excess of aniline to the conclusion of theprocess. The retort is fitted with a mechanical agitator, whose axis moves ina tube serving as a passage for a current of steam. (See Fig. 19.) Into

this apparatus are introduced—

Acetate of rosaniline.5 kilos.

Aniline.13 „

Heat is then applied, and the temperature is kept close upon 170° C., by meansof a thermometer plunged in the retort. The operation lasts about two hours,its progress being judged by withdrawing successively small portions with arod, and dissolving them in alcohol and acetic acid upon a piece of whiteporcelain. The spot ought to be entirely and purely blue. If there is a toodecided red halo round the streak the operation is not complete. If the halois of a sallow, brown, or greyish-green tint, the process has been carried toofar. In a well-managed operation the blue should remain dissolved in theexcess of aniline, and when the reaction is over the mass should appear semi-fluid, but perfectly homogeneous. The retort is then raised up by means ofpulleys, and the screws which secure its head to the boiler are undone, so thatthe contents may be poured out.

The crude mass is treated differently, according to the kind of colourdesired. For the common blues, all that is required is the separation of theblue from the excess of aniline. One method for attaining this objedt consistsin sweeping the aniline mechanically away by a current of steam. In theother method it is removed by washing with dilute acids. The residue is thenfit for sale.