Application of Mordants. 379 



Bleaching the calico. — According as the calico is intended 

 for block and cylinder printing, or for a white ground, the 

 bleaching varies. 



In calico for block and cylinder printing, the bleaching 

 does not require to reach the internal parts of the fibre ; a 

 superficial whiteness is sufficient. It is sufficient, therefore, 

 to cleanse the cloth by means of warm bran water and 

 yest, in order to remove the weaver's dressing; then alter- 

 nately to boil it with ley, and to bring it into a sulphuric 

 acid bath, and lastly to lay it out in the sun. 



For white grounds, it is necessary to carry the bleaching 

 into the internal parts of the threads, Otherwise the 

 colours are forced into the ground and bleached spots are 

 produced. When, therefore, the cloth has been prepared 

 by cleansing and alternate treatment with ley and acid, the 

 bleaching in the sun should be combined with the use of 

 chloride of lime and chloride of soda. The cloth should 

 be placed in very weak solutions of these. 



To remove the colours which are deposited upon improper 

 places, as on white grounds, bran and soap-suds are em- 

 ployed alternately with the action of the sun. The neces- 

 sary process is given under soap-suds. 



In madder colours with a white ground, chloride of soda 

 assists powerfully, in making the madder-red more red, 

 and the white more white. 



For the purpose mentioned, the chloride of soda may 

 also be employed when mixed with soap-suds. This mix- 

 ture gives the madder-red more lustre. — (See Turkey-red 

 manufacture). Chloride of soda must be employed in a 

 very dilute state. The degree of dilution depends upon the 

 depth of colour, and must be determined by trial. When 

 the chloride of soda is too strong, it acts too rapidly, and 

 imparts to the cotton an appearance, as if a white powder 

 was laid over it. This proceeds from the fine threads being- 

 bleached white before the chlorine has had time to act 

 upon the twisted threads. 



Application of mordants to calico. — This process con- 

 stitutes the basis of the dyeing of calico. It depends on 

 the circumstance, that certain earths and metals when they 

 are dissolved in water by the assistance of acids, combine 

 intimately with the cotton fibre, and that these combinations 



