ANILINE BLACK.

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dissolved 6 kilos, of aldehyde are added, and the mixture is allowed to standfor four or five hours. At the expiration of this time it is poured into water.The grey colouring matter dissolves, and the solution, previously filtered, isprecipitated with common salt. These solutions and precipitations- are re-peated until the produd is sufficiently pure. This preparation dyes a fine greyupon linen and cotton, but its price is hitherto very high.

Carvis and Thirault prepare a grey (mureine) by dissolving bichromate ofpotassa and a salt of iron in dilute sulphuric acid, and allowing the mixture toread upon a bi-salt of aniline, preferably the hydrochlorate.

By varying the respective proportions of the bichromate, of the iron salt,and of the salt of aniline, or by employing other acid salts of the latter, greysmay be obtained of a reddish or bluish tone, all which, according to thepatentees, are soluble in boiling water, and resist acids and soap better thangreys produced by other methods.

ANILINE BLACK.

This differs remarkably from the rest of the aniline colours. It is not adefinite chemical compound, but a mixture of at least two distinct colours,—the one an intense blue, bordering upon black, and the other a very deepbrown. It is produced by the adtion of powerful oxidising agents upon amixture of aniline and toluidine.

This colour is completely insoluble in water, alcohol, ether, benzol, boilingsoap-lyes, acids, and alkalies. It has a full, rich, velvety shade, which isturned to a green by acids and restored to its original shade by alkalies.Dilute bichromate of potash increases the intensity of the shade, but, if con-centrated, turns it to a reddish hue. Chlorine and the alkaline hypochloritesdestroy it in course of time. But if the adtion has not been sufficiently pro-longed for the total destruction of the black, but has merely turned it to agarnet-red shade, the original black gradually returns on exposure to the air,and finally regains its former intensity.

Aniline black has a more powerful affinity for vegetable than for animalfibres. Whether all the various processes for the preparation of aniline blackyield products chemically identical is open to question. That it cannot, asmaintained by some authorities, consist of mere mixtures of ordinary anilinecolours, is proved both by its feebler affinity for wool and silk, and by its inso-lubility in the usual solvents. Some aniline blacks resist more or less theaCtion of light and of chemical reagents, whilst others turn green more or lessreadily in contact with air containing acid or sulphurous fumes. The moreintense an aniline black, the better it resists these agencies. A black deve-loped in presence of excess of aniline is always more stable than one equallyconcentrated developed in presence of an excess of acid. Hence the latterclass of blacks are unsafe. The tissue is weakened, the black obtained easilyturns green, and will not bear bleaching liquor. If the gas used in a ware-house where goods dyed or printed an aniline black are stored should containa little sulphur, the folds of all the pieces may be turned greenish by the sul-phurous acid. When a colour is formed containing excess of base the blackwill be less likely to turn green, and is better able to bear the adtion ofbleaching liquor. In order that such a black may satisfy all practical condi-tlQ ns, it must be developed with sufficient rapidity to avoid the volatilisation