BLEACHING 



BLEACHING OF WOOL. 



Wool, like tho proofing fibrous matter, is covered with a peculiar varnish, which 

 impairs its qualities, and prevents it from being employed in the raw state for the 

 purposes to which it is well adapted when it is scoured. Tho English give tho name 

 yolk, and the French suint, to that native coat : it is a fatty unctuous matter, of a 

 strong smell, which apparently has its chief origin in tho cutaneous perspiration of 

 tho sheep ; but which, by the agency of external bodies, may have undergone some 

 changes which modify its constitution. It results from the experiments of M. Vauquc- 

 lin, that the yolk is composed of several substances ; namely, 1, a soap with basis of 

 potash, which .constitutes tho greater part of it ; 2, of a notable quantity of acetate of 

 potash ; 3, of a small quantity of carbonate, and a trace of chloride of potassium ; 4, 

 of a little lime in an unknown state of combination ; 5, of a species of sebaceous 

 matter, and an animal substance to which tho odour is duo. There are several other 

 accidental matters present on sheep's wool. 



The proportion of yolk is variable in different kinds of wool, but in general it is 

 more abundant tho finer tho staple ; the loss by scouring being 45 per cent, for tho 

 finest wools, and 35 per cent, for the coarse. 



The yolk, on account of its soapy nature, dissolves readily in water, with the 

 exception of a little free fatty matter, which easily separates from the filaments, and 

 remains floating in the liquor. It would then appear sufficient to expose the wools to 

 simple washing in a stream of water; yet experience shows that this method never 

 answers so well as that usually adopted, which consists in steeping tho wool for some 

 time in simple warm water, or in warm water mixed with a fourth of stale urine. 

 From 15 to 20 minutes of contact are sufficient in this case, if wo heat the bath as 

 warm as the hand can bear it, and stir it well with a rod. At the end of this time 

 the wool may be taken out, set to drain, then placed in large baskets, in order to be 

 completely rinsed in a stream of water. 



It is generally supposed that putrid urine acts on the wool by the ammonia which 

 it contains, and that this serves to saponify tho remainder of the fatty matter not 

 combined with tho potash, although M. Vauquelin gave another opinion. Fresh urine 

 contains a free acid, which, by decomposing the potash-soap of the yolk, counteracts 

 tho scouring operation. 



If wools are better scoured in a small quantity of water than in a great stream, wo 

 can conceive that this circumstance must depend upon the nature of the yolk, which, 

 in a concentrated solution, acts like a saponaceous compound, and thus contributes 

 to remove the free fatty particles which adhere to the filaments. It should also be 

 observed that too long a continuance of tho wool in the yolk water, hurts its quality 

 very much, by weakening its cohesion, causing the filaments to swell, and even to 

 split. It is said then to have lost its nerve. Another circumstance in tho scouring of 

 wool, that should always be attended to, is never to work tho filaments together to 

 such a degree as to occasion their felting ; but in agitating we must merely push 

 them slowly round in the vessel, or press them gently under tho feet. Were it at all 

 felted, it would neither card nor spin well. 



As the heat of boiling water is apt to decompose woollen fibres, we should be careful 

 never to raise the temperature of tho scouring bath to near this point, nor, in fact, to 

 exceed 140 F. Some authors recommend tho use of alkaline or soapy baths for 

 scouring wool, but practical people do not deviate from the method above described. 



When the washing is completed, all the wool which is to be sent white into tho 

 market, must bo exposed to the action of sulphurous acid, either in a liquid or a 

 gaseous state. In tho latter case, sulphur is burned in a close chamber, in which the 

 wools are hung up or spread out ; in the former, the wools are plunged into water 

 moderately impregnated with the acid. (See SULPHUHIXO.) Exposure on the grass 

 may also contribute to tho bleaching of wool. Some fraudulent dealers are accused 

 of dipping wools in buttermilk, or chalk-and-water, in order to whiten them and 

 increase their weight. 



Wool is sometimes whitened in the fleece, and sometimes in tho state of yarn ; tho 

 latter affording tho best means of operating. It lias been observed that tho wool cut 

 from certain parts of the sheep, especially from the groin, never bleaches well. 



After sulphuring, tho wool has a harsh crispy feel, which may be removed by a 

 weak soap-bath. To this also the wool-comber has recourse when he wishes to 

 cleanse and whiten his wools to the utmost. lie generally uses a soft or potash soap, 

 and after tho wool is well soaked in tho warm soap-bath, with gentle pressure ho 

 wrings it well with the help of a hook, fixed at tho end of his washing-tub, and hangs 

 it up to dry. 



The actual operations of purifying wool are so blended with the methods of weav- 



