480

DYEING AND CALICO PRINTING.

water and 200 kilos, of pastel are heated to 95 0 C. by the aid of steam ; aftersome few hours there are added 6 kilos, of indigo, 8 kilos, of madder, 2 kilos,of bran, 4 kilos, of lime, and 4 kilos, of potash (pearl-ash) : this mixture isstirred up every three hours during the first forty-eight hours after having beenmade : when the redudtion of the indigo goes on well, there are still added6 kilos, of indigo and 1 kilo, of madder. The contents of the vat are nextstirred up from time to time, and then left at rest till the next day. Thetemperature of the vat is kept up at from 40° to 50° C.; after each day’s workthere is added to this vat a quantity of i'5 kilos, of madder, and every thirdday 6 kilos, of indigo. When this vat is once put into proper working orderit lasts for several months.

The so-called Indian, or potash vat, employed for dyeing wool andsilk, is made up with bran, madder, indigo, and potash ; the indigo is onlyadded to the mixture of water, and the other ingredients after they havebeen heated up to 90° C.; afterwards the temperature is kept up to between30° and 40° C., the mixture being thoroughly stirred up once in every twelvehours for a period of forty-eight hours. The colour of the liquid should be agreenish-yellow with a coppery hue, and bluish-coloured scum on the surface.The quantities employed are—Indigo, 8 kilos.; potash (pearl-ash), 12 kilos.;bran and madder, each 3-5 kilos. In order to keep up this vat there are addedto it, when required, certain quantities of alkali, indigo, and madder. Thiskind of vat is more readily managed, not so easily spoiled, and works quicker,

_that is to say, it is possible to dye three times as much wool in it in the

same time, and, moreover, the dyed fabric does not, on being washed in soap,cast off so much superfluous dye as with the pastel-vats; but this alkali-vathas to be refreshed about every twenty-five to thirty days, because the potashbecomes soon saturated with the fat and grease of the wool.

More advantageous than the Indian is the vat generally known as theGerman, employed not only in that country, but also elsewhere. To thewater, having been first heated to 95“ C., are added 20 pailfuls of bran, 11 kilos,of carbonate of soda, 5-5 kilos, of indigo, and 2'5 kilos, of lime just slakedpreviously, while the temperature is kept up at from 40° to 50° C.: fermentationsets in after about twelve hours; the liquid gives off a somewhat sour smell,becomes coloured a greenish-blue, and gives off gas-bubbles : from time totime the same quantities of indigo, soda, and lime are added, and, moreover,some 3 to 4 kilos, of molasses : the vat is fit for use after the third day. Sincesoda is much cheaper than potash, this vat is more economical for that reason.The German vat may last, in good working order, for fully two years.

The fermentation indigo-vats are subjedt to diseases , which are more espe-cially to be feared with the pastel-vats. The more frequently occurringdiseases are due either to an excess or to a deficiency of lime : in the first-named instance the colour of the liquid becomes more and more clear andbright, the bluish scum decreases, and the odour disappearing, fermentationstops, and the adtive principles are precipitated : when this defedt is discoveredin good time, it is remedied by the addition of sulphate of iron. In case therehappens to be a deficiency of lime, the fermentation becomes first too adtive,and next enters the putrescent stage. The liquid turns red, and, if vattedcloth is plunged into it, it is soon decolourised. The only remedy for thisdisease is to heat the liquid to go 0 , and to add lime; if this does not arrest the