For the purposes of the carpet yarn dyer, at any rate, the anilines and alizarines now obtainable are infinitely preferable to any natural or vegetable dyes, being easier to use, more reliable, and faster to light.
The ordinary method of preparing the dye-bath into which the worsted or woollen yarn is to be dipped in the manner that has been described, is as follows. The water, in which from 2 to 4 per cent. of sulphuric acid and from 5 to 10 per cent. of Glauber’s Salts is mixed, is brought up to about 170°F.; the dyestuff is added, about 1 to 5 per cent., according to the depth of shade required. The percentages are reckoned upon the weight of the yarn to be dyed. The yarn is then entered, and the water is brought to the boil, and kept lightly boiling as long as required to obtain the shade. There are some delicate shades, however, and some sensitive dyestuffs, for which the yarn requires to be entered cool, and the water to be brought slowly to the boil.
The dyed yarn passes from the vat to the hydro-extractor, a large copper pan with perforated sides, which, revolving at a great speed, causes the wet skeins by centrifugal force to press against the circumference and squeeze out a large proportion of the water they contain. The skeins are then taken out, bundled roughly together, and are ready for conveying to the drying room or drying machine.
Drying the yarn can be effected simply by hanging the skeins on poles in a room through which strong currents of air are forced by revolving fans. This method, however, depends too much upon the weather, even if the air is caused to pass over steam-heated coils on entering the room. A better alternative is to expose the yarn hung on poles in a heated chamber. The most certain and satisfactory method, however, is a drying machine of some type, which enables the skeins to be fed into it at one end, to pass through a current of heated air, and to be delivered dry at the other. The factors in this case, the heat of the steam coils and the speed of the machine, are known and can be controlled; so that the dyer can rely upon getting a certain quantity of yarn satisfactorily dried in a certain time. In the ordinary type of machine, the skeins are carried horizontally between two wire aprons; but alternatively they can be carried vertically upon hooks or poles.