288 Cellulose 



moreover, the bleaching solutions are used in a highly dilute 

 form (0-5-2-0 p.ct. bleaching powder). In papermakers' 

 cellulose bleaches, while it is true that by far the greater pro- 

 portion of the chemical work of purification is thrown upon the 

 pulping process, the consumption of bleaching powder in the 

 bleaching process proper is in some cases considerable. In 

 the bleaching of rag pulp (cotton and linen) the average con- 

 sumption is from 2-5 p.ct. ; in straw and esparto pulp, 10-15 

 p.ct ; and sulphite wood pulp, 15-25 p.ct. In these latter cases 

 we have a further illustration of * overhead ' treatments i.e. in 

 order to produce a certain result in a given time and a single 

 process, a large amount of waste energy is expended. These 

 celluloses are, as we have already seen, very different constitu- 

 tionally from the normal type : they are easily hydrolysed, and 

 in the alkaline bleach liquor a considerable further proportion 

 of the fibre-constituents are dissolved and undergo oxidation of 

 a perfectly useless character. To minimise these wastes of the 

 oxidising agent, the practice of intermediate washing is some- 

 times resorted to ; and by thus separating the effects of hydro- 

 lysis and oxidation, the latter is controlled into the directions of 

 useful, i.e. bleaching oxidations. The economy of bleaching 

 powder which results is very considerable, and it is not a little 

 remarkable that so rational a plan is not more generally 

 adopted. 1 



Of the textile bleaches of this group there are two which 

 may be selected to illustrate general principles, viz. the cotton 

 bleach and the linen full bleach. 



In COTTON-CLOTH BLEACHING the most important process 

 is the alkali boil. The treatment is varied to suit the great 

 variety of goods which undergo the process, but for our present 



1 A very thorough treatment of papermakers' bleaching processes will 

 be found in Griffin and Little's 'Chemistry of Paper Making '(1894), 

 chap. v. pp. 275-300. 



