The Dyeing of Woollen Fabrics | Page 7

fibre, leaving the latter in such a condition that by washing with water the rest of the impurities in the wool can be extracted. By distilling off and recondensing the solvent can be recovered for future use, while the wool fat can also be obtained in a condition to use for various purposes. This is rather a more scientific method than the old one, but it has not as yet come into extensive use.
#Wool Scouring. Old Methods.#--In the early days of wool scouring (p. 017) this operation was done in a very primitive fashion, generally in a few tubs, which could be heated by steam or otherwise, and in which wool was worked by means of hand forks. These primitive processes are still in use in some small works, especially where the wool is dyed in the loose condition, but in all the large works machinery has been adopted, which machinery has been brought to a high state of perfection, and does its work very well, and without much attendant manual labour.
The alkaline substances used in this process of scouring demand some notice. These comprise soda ash, soda crystals, caustic soda, silicate of soda, potash, caustic potash, soaps of various kinds, stale urine, ammoniacal compounds. Which of these may be used in any particular case depends upon a variety of reasons. Potash is the best alkaline agent to use. It agrees better with the fibre than any other, leaving it soft and elastic. Ammonia is the next best, but it does not take out the grease as well as the potash. Soda does not suit as well as potash, as it has a tendency to leave the fibre harsh in feel and somewhat brittle, yet on account of its being so much cheaper it is the most largely used. The use of silicate of soda cannot be recommended, as it has a great tendency to leave the fibre hard, which may be ascribed to the deposition of silica on the fibre.
The caustic alkalies cannot be used as they have too solvent an action on the fibre. The carbonates, therefore, in the form of soda ash or potash, or pearl ash, are used, or better still, soap is used as it has a greater solvent action on the fatty matter of the wool than have the alkalies, and in this respect a potash soap is better than a soda soap.
The character of the wool determines the alkali to be used; fine, long-stapled wools, which are usually very free from grease in excess, should always be treated with potash, or a potash soap, which will (p. 018) remove the whole of the grease from the wool, leaving the latter in a fine, soft, silky condition.
Short-stapled wools can be treated with soap and a little soda ash, but too much of the latter is to be avoided. Coarse and greasy wools may be scoured with soap and soda ash, or other alkali which is almost necessary to remove the large amount of grease these wools contain.
Practically the only alkaline products now in use are the various hard and soft soaps, and the carbonates of soda and potash in their various forms of soda ash, soda crystals, potashes, pearl ash, etc. Ammonia and its compounds are rarely used, while stale urine, which acts in virtue of the ammonia it contains has practically gone out of use.
#Hand-Scouring.#--Wool scouring by hand is easily done and requires few appliances, simple tubs or vats of sufficient capacity in which steam pipes are placed, so that the scouring liquors can be heated up. The best temperatures to use are about 130�� to 140��?F., and it is not advisable to exceed the latter, as there is then some risk that the alkali may act on the fibre too strongly.
The strength of the scouring liquor necessarily varies with the kind of wool being treated, and with the kind of alkaline product used; if soft, fine wools are being treated, then the liquor may be made with 1 to 2?lb. of soap to 10 gallons of water (if a mixture of soap and alkali is used, then it may contain from 1/4 to 1/2?lb. soda ash, and 1/2?lb. to 1?lb. of soap). For coarse, greasy wools these quantities may be increased by about one-half. The best plan of scouring by hand is to treat the wool in a tub with a scouring liquor for about half an hour, then to squeeze out the surplus liquor and to treat again in a new liquor for half an hour; this liquor may be used for a new batch of wool. The wool is often put into nets, and these are lifted up and down in the liquor so as to cause it to penetrate to every part of the wool.
It is not advisable to