214

DYEING AND CALICO PRINTING.

with constant stirring, 1000 grms. of tartaric acid dissolved in i litre of water.To prepare this colour for printing, boil i litre of this mixture filtered,with 135 grms. of starch and the same weight of dextrine, and just beforeprinting add 60 grms. sulphide of copper. Spirk ages for twenty-four toforty-eight hours, at the temperature of 25 0 to 30° C. The pieces are thenpassed through an alkaline bath at 75 0 C., and lastly through a soap bath at75 0 to 8o° C. If the white grounds appear dull they are passed through weakbleaching-liquor. In the preparation of aniline blacks Hartmann recommendsthe selection of anilines whose boiling-points lie between 180° to 185° C., andrejetts as useless all samples boiling above 192 0 C., as giving dirty browns orother useless colours.

The best methods of dyeing aniline blacks have also been investigated byPersoz, whose results may be instructive. Some time ago the attempt wasmade to dye cottons black by passing them through a solution of an anilinesalt mixed with bichromate of potash. If the solutions were strong, thecolour appeared as soon as the goods left the bath, and speedily became fullydeveloped. A serious difficulty, however, was encountered. If the liquidswere dilute no black was produced, and if concentrated the colour was preci-pitated in the bath. It was attempted to obviate this difficulty by cooling thesolutions down to near the freezing-point. This was no improvement, as thechromate of aniline crystallises out, weakening the bath, and causing spots byadhering to the pieces, which were sometimes even charred by the rise oftemperature taking place on lifting them out of the solution. , Persoz, toovercome these difficulties, causes the pieces to pass through a spray producedby the rapid rotation of brushes in each of the solutions. The same authorhas examined which aniline salts are practically best suited for dyeing agood black. ' The tartrate, oxalate, and citrate are either too dear or unfavour-able. The experiments were consequently limited to the sulphate, nitrate,and hydrochlorate of aniline. He finds that, for dyeing, the employment ofthe neutral aniline salts is to be avoided ; the binacid salts, especially thebisulphate, give good results, though among the hydrochlorates the teracidsalt is preferable. A mixture of bisulphate and terhydrochlorate of anilinegives the best results, the reddish cast of the one being compensated by theblue shade of the other. The solution of bichromate of potash should beused in a concentrated form, not less than 80 grms. per litre.

It makes little difference in the results if the bichromate of potash isapplied before or after the aniline salts, or at the same time. The texturemay therefore be completely impregnated with the bichromate solution, andimmediately after exposed to the spray of the aniline solution. The blackappears at first dark green. To develope the colour it is only necessary towash the goods in water, and then pass through a hot soap bath.

It has been already mentioned that aniline black has a greater affinity forvegetable than for animal blacks. In 1865 Mr. Lightfoot patented a processfor applying the aniline black to wool. A solution is prepared with 1 kilo, ofdry hypochlorite of lime to 10 litres of water for every kilo, of wool. This

bath is composed of—

Water.60 litres.

Solution chloride of lime. 1*3 kilos.

Hydrochloric acid .180 grms.