446

DYEING AND CALICO PRINTING.

M. Gros-Renaud’s researches* gave in many aspects analogous results.When indigo-carmine (that is to say, sulphindigotate of soda as met with intrade) is suspended in water, and there is added to that mixture a caustic sodalye, of sp. gr. i'333, containing about 30 per cent of dry caustic soda, there isobtained a yellow liquid and a black precipitate, soluble in water, with a bluecolour. If to the yellow liquid strong sulphuric acid is added a few hoursafter it (the liquid) has been prepared it becomes blue, this colouration beingpermanent; if the acid, is only added after twenty-four hours the liquidbecomes first green, next red, and at last violet. When the yellow-colouredliquid is strongly acidified forty-eight hours after having been prepared itbecomes rapidly red after having passed through a variety of intermediatehues. This red liquid dyes, if previously incompletely saturated with car-bonate of soda, unmordanted wool, imparting to it tints varying from rose todeep amaranth-red, according to the concentration of the liquid and the lengthof the immersion of the wool, as well as the temperature. The violet-coloured liquid just before mentioned dyes wool violet. This red substancediffers essentially from sulphophenicic and sulphopurpuric acids, being farmore soluble in water, and becoming immediately yellow on the addition ofa small quantity of caustic soda, but being rendered violet again by the additionof as much sulphuric acid as is necessary to neutralise the alkali. Acetate oflead does not form with the red matter any precipitate. Wool which hasbeen dyed amaranth with this red matter yields, when treated with strongsulphuric acid, a red liquid, while wool which has been dyed with sulpho-purpuric acid yields, under the same conditions, a blue liquor. The pro-duction of red or amaranth dyes upon wool with sulphopurpuric acid requires,after dyeing, an alkaline bath, which is unnecessary for the red liquor just named.

When caustic soda is made to aCt for three days upon a mixture of sulph-indigotic and sulphopurpuric acids, and the liquid next supersaturated withconcentrated sulphuric acid, there results a red liquid and a yellowish brownprecipitate. This latter having been collected on a filter, and more or lesswashed, dyes deeper or lighter yellow shades, according to the more or lesscomplete washing of the precipitate. It has not been hitherto possible toreproduce indigotin from its sulphuric acid derivatives, though frequentattempts have been made.

When indigotin is heated up to 180° along with chloride of benzoyl theformer body is converted, with evolution of hydrochloric acid, into a brownmatter, which fuses at 108°. It is soluble in alcohol and ether, and consistsof a benzoic indigotin compound, C 8 H 4 (C 7 H 5 0 )NO.f

Isatin is a coloured matter, but not a tinctorial product, about which, how-ever, since it is an immediate derivative from indigotin, and, moreover, formedduring some of the industrial applications of that body, viz., during the appli-cation of the discharge style upon blue-dyed grounds by means of oxidisingsubstances, we give the following particulars:—Isatin is produced by theaction of oxidising agents upon indigotin, such as chlorine water, dilute nitricacid, chromic acid, ferricyanide of potassium, and caustic alkalies. It isbest prepared by mixing 1 kilo, of finely pulverised indigo with water, so asto form a thickish paste, to which, while being gently heated, there are

* “ Bulletins de la Socicte Industrielle :le Mulhouse,” vol. xxiv,, p. 343.

t “ Comptcs ^endue de J’Academie ties Sciences,” lvi., p. 1050.