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Indigo Blue Dye for Yarn

The 2 gills hydrochloric acid, and 4 ounces tin vats used for dyeing indigo blue are usually crystals. The Prussiate tub is made up by wine pipes or other large casks, sunk in the dissolving in it 1 pound ferrocyanide of poof poground to a depth convenient for the operators tassium, and adding 1 wine -glassful of sulto work at. Five of these constitute a set, phuric acid, and 1 of hydrochloric acid. If and are worked together and kept of the same not dark enough with putting through once, through once, strength. The yarn being worked in quanti- repeat. ties of 100 pounds, 20 pounds are passed through each vat.

Each vat is filled about three-fourths with cold water; there are then added 8 pounds of indigo, 16 pounds of sulphate of iron (copperas), and 24 pounds newly-slaked lime. The whole is well stirred with a rake for half an hour, and this stirring is repeated every 1½ hours for the first day.

The time to stop the stirring is known by the solution becoming a rich oak yellow, having large blue veins running through it and a fine indigo froth on the surface. When these signs are all favorable, the solution is allowed to stand for several hours till all the solid matter settles, when it is ready for use.

The mode of dyeing consists in simply immersing the goods, and working them in the solution for 15 minutes, taking out and wringing or pressing, and then exposing to the air; repeating this operation until the desired depth of color is obtained. The yarn is then washed in cold water and dried. When the shade required is very deep, the yarn may, previous to washing, be passed through a tub of water acidulated with vitriol till it tastes acid, and then washed; this adds brilliancy to the color.