The Dyeing of Woollen Fabrics | Page 6

naturally imparted by the absorbed metallic salt.
The normal salts of the alkaline metals, such as sodium chloride, potassium sulphate, sodium sulphate, etc., have no action whatever on the wool fibre.
Wool has a strong affinity for many colouring matters. For some of the natural colours, turmeric, saffron, anotta, etc., and for the neutral and basic coal-tar colours it has a direct affinity, and will combine with them from their aqueous solutions. Wool is of a very permeable character, so that it is readily penetrated by dye liquors; in the case of wool fabrics much depends, however, upon the amount of felting to which the fabric has been subjected.
If wool be boiled in water for a considerable time it will be observed that it loses much of its beautiful lustre, feels harsher to the touch, and also becomes felted and matted together. This has to be carefully guarded against in all dyeing operations, where the handling or moving of the yarns is apt to produce this unfortunate effect.
After prolonged boiling the fibre shows signs of slight decomposition, from the traces of sulphuretted hydrogen and ammonia gases which it evolves.
When wool is dried at 212��?F. it assumes a husky, harsh feel, and its strength is perceptibly impaired. According to Dr. Bowman, the wool fibre really undergoes a slight chemical change at this temperature, which becomes more obvious at 230��?F., while at about 260��?F. the fibre begins to disintegrate. According to the researches of Persoz, however, temperatures ranging from 260��?F. to 380��?F. can be employed without any harm to the wool, if it has previously been soaked in a 10 per cent. solution of glycerine.
When wool is heated to 212��?F. (100��?Cent.) it becomes quite (p. 014) pliant and plastic and may be moulded into almost any shape, which it still retains when cold. This fact is of much interest in the processes of finishing various goods, of embossing velvet where designs are stamped on the woven fabric while hot, and in the crabbing and steaming of woollen goods, making hats, etc.
CHAPTER II.
(p. 015)
PROCESSES PREPARATORY TO DYEING, SCOURING AND BLEACHING OF WOOL.
Wool scouring takes place at two stages in the process of manufacture into cloth. First, in the raw state, to free the wool from the large amount of grease and dirt it naturally contains; second, after being manufactured into cloth, it is again scoured to free it from the oil that has been added to the scoured raw wool to enable it to spin easily. This oiling is generally known as wool batching, and before the spun yarns or woven fabrics can be dyed it is necessary to remove it.
Raw wool is a very impure substance, containing comparatively little wool fibre, rarely more than 50 to 60 per cent. in the cleanest fleeces, while it may be as low as 25 per cent. in the dirtiest.
First there is a small quantity of dirt; there is what is called the suint, a kind of soapy matter, which can be removed by washing in hot water. This soap has for its base potash, while its acids are numerous and complex. The wool contains a fatty-like substance of the nature of wax, called cholesterine, and this imparts to the fatty matter, which be extracted from the wool fibre, very peculiar properties. Besides these there are several other bodies of minor importance, all of which have to be removed from the wool before it can be manufactured into cloth.
Marker and Schulz give the following analysis of a good sample of (p. 016) raw wool:--
Moisture 23��48 per cent. Wool fat 7��17 " Wool soap (suint), soluble in water 21��13 " Soluble in alcohol 0��35 " Soluble in ether 0��29 " Soluble in dilute hydrochloric acid 1��45 " Wool fibre 43��20 " Dirt 2��93 " ------ 100��00
Two principles underlie the methods which are in use for this purpose. The first principle and the one on which the oldest method is based is the abstraction of the whole of the grease, etc., from the wool by means of an alkaline or soapy liquor at one operation. This cannot nowadays be considered a scientific method. Although it extracts the grease, etc., from the wool, and leaves the latter in a good condition for after processes, yet with it one might almost say that the whole of the soap or alkali used, as well as the wool grease itself, is lost as a waste product; whereas any good process should aim at obtaining the wool grease for use in some form or another. The second principle which underlies all the most recent methods for extracting the grease from the wool, consists in treating the fibre with some solvent like benzol, carbon bisulphide, petroleum spirit, carbon tetrachloride, etc., which dissolves out the cholesterine and any other free fatty matter which is in the wool