BLEACHING. I7I 



action of steam is very efficacious in bleaching 

 cottons. 



In bleaching cotton for calico-printing, a pure 

 white is not so much sought for, as that the oil 

 may be entirely extracted. 



In applying the alcaline ley, great care must be 

 taken that no lime remains in suspension in the 

 liquor, as it might be fixed in the cloths ; and when 

 the sulphuric acid is used, a sulphate of lime would 

 be formed, which in fact is a mordant for the 

 madder ; hence the latter could not be discharged 

 from those parts intended to be white. 



For the same reason, the oxy muriate of lime can- 

 not be used, if madder is to be discharged from 

 any part of the cloth. When this is the case, oxy- 

 muriate of potash, or of soda, is substituted for 

 oxymuriate of lime. 



Bleaching of Wool. 



The bleaching of animal substances is somewhat 

 different from the processes employed for vegetable 

 substances. 



Wool is a sort of very fine hair which covers the 

 bodies of some animals. Each hair is hollow, and 

 contains an oily matter. 



Wool is not easily acted upon by acids ; is unalter- 

 able by water, cold or boiling; but may be entirely 

 dissolved by strong alcaline leys. On this account, 

 the latter must be used with great caution. 



Wool is oiled before it is combed and spun, and 

 the first operation is to free it from the oil which 

 it has thus acquired. This is called scouring. Stale 

 urine, which contains ammonia or the volatile 

 ^Icali, is mixed with water ; and the wool is im- 



