INDIGO.

485

After printing on all the patterns, the cloth is kept for some time before under-going other processes, in order to give time for the oxidation of the acetate ofiron, whereby the indigo is made to adhere more firmly, and the risk of itsbecoming detached from the cloth, when the latter is immersed in the tanks,is prevented. If this precaution is negledted, the shade becomes unequal.Six tanks are employed in this process,—viz., two lime tanks, eachcontaining 12*5 kilos, of slaked lime; one copperas tank, at a strength of7 0 Baume (1*048 sp. gr.); one tank containing caustic soda (sp. gr. i*ioi) ; atank containing 500 grms. of strong sulphuric acid to each pailful of water;and, lastly, a tank with good fresh water. The goods are left for a quarter of anhour in the first lime-water tank, care being taken to impart to the piece a slightmovement upwards and downwards ; next, the pieces are immersed in thecopperas tank, and left therein quietly for a quarter of an hour; next, anotherquarter of an hour in the second lime tank; and after that again a quarter ofan hour in the copperas, followed by a stay of five minutes in the caustic soda,and half an hour in the dilute sulphuric acid, wherein the pieces are thoroughlymoved about and rinsed, and from this bath they are lastly transferred to theclean water bath. After the passing of each piece through the lime-watertanks, there is added to each of these 2 kilos, of freshly-slaked lime, while50 kilos, of copperas are added to refresh the tank of this material afterten pieces have been passed through it. The soda tank is kept in workingorder by the addition of about 4 kilos, of caustic soda after the passage ofevery five pieces. The tank containing the sulphuric acid is kept up by theaddition of 25 kilos, of acid after five pieces have been passed through, while,moreover, the contents of this tank are thrown away as soon as it is dirty, afreshly-filled supplementary tank being in readiness.

The experience of M. E. Schwartz, of Bale and Mulhouse, has proved that,in order to make this method of working successful, the soda ought to bethoroughly caustic, and kept up at the above-quoted strength, while it is alsoessential that the copperas solution should be neutral, for which purpose thesolution is boiled with some clean scrap iron. After the goods have beenwashed in the fresh-water tank, they are thoroughly washed in a current ofwater, and next left over night in a very weak solution of sulphuric acid(sp. gr. 1*007), * n order thereby to remove the last traces of peroxide of iron.The next morning the goods are again washed in cold water, and afterwardspassed through hot soap-water (temperature 50°).

So-called China green is obtained by adding to the colour mixture some bi-chloride and nitro-muriate of tin. The blue colour is fixed as above described,but the goods are only left for two minutes in the soda and five minutes in theacid tank. After washing, the pieces are dyed with quercitron.

Very dark shades cannot be obtained in the China blue style: it is a fastcolour, but expensive, on account of the time and labour it requires, especiallyif carried out by the old process of dipping the goods attached on frames : bythe more modern method, described above, the vats (tanks) are supplied withrollers, and the pieces passed through quickly ; time is saved, but it is at theexpense of the quality.

A resist for China blue, if required, maybe obtained by thickening a mixtureof sulphate of copper, acetate of lead, nitrate of copper, and lime-juice.

Fast blue and green colours are now produced upon calico (printed on) by a