4. The chamber.—The interior height of the chamber, A B C D, [fig. 245.], is 9 feet, the length 12 feet, and the breadth 9 feet. The steam is introduced into it by two pipes, a b c, d e f. Their two ends, d c, are shut; but their sides are all along perforated with small holes. The frames E F G H, E F G H, are moveable, and run upon rollers: they are taken out by front doors, which are made of strong planks, shut by sliding in slots, and are secured by strong iron bars and pressure screws. The cross rods, E F G H, are provided with hooks for hanging up the pieces. There is a safety-valve in the top of this large chamber. The dimensions of the frame are 10 feet long, 3 feet wide, and 7 high. Three feet and a half from the upper part of the frame, a row of hooks is fixed for hanging on a double row of pieces, as shown in the figure. Over the frame, woollen blankets are laid to protect it from drops of water that might fall from the roof of the chamber. When the hooks are two thirds of an inch apart, 24 pieces, of 28 yards each, may be suspended at once. The period of steaming is from 45 to 60 minutes.
Muslins and silks do not require so high a temperature as woollen goods. When the stuffs are padded with colour, like merinos and chalys, they must not be folded together, for fear of stains, which are sometimes occasioned by the column in steam calico-printing, where the end which receives the first impression of the steam is seldom of the same shade as the rest of the roll of goods. The duration of the steaming depends upon the quantity of acid in the mordant, and of saline solution in the topical colour; the more of which are present, the shorter should be the steaming period. A dry vapour is requisite in all cases; for when it becomes moist, from a feeble supply or external condensation, the goods become streaky or stained by the spreading of the colours.
1. Black figures are given by decoction of logwood thickened with starch, to which a little oxalic acid is added while hot, and, after it is cold, neutralised solution of nitrate of iron.
2. Dark blue for a ground.—Decoction of logwood, and archil thickened with starch; to which, while the paste is hot, a little soluble Prussian blue is added; and, when it is cold, neutralised nitrate of iron; see supra.
3. Deep poppy or ponceau colour.—Cochineal boiled in starch water, with oxalic acid (or tartaric), and perchloride of tin.
4. Rose.—Cochineal infusion; oxalic acid; perchloride of tin; thickened with gum.
5. Dark amaranth.—Decoctions of archil and cochineal, thickened with starch: to the paste, alum and perchloride of tin are added.