Supplementary Chapter 313 



by treatments which are not marked by change of weight of 

 the cellulose, nor by visible structural modification. 



It is evident that the standard ' pure cellulose ' and the 

 criteria of purity adopted by (a) the calico printer in his 

 * madder (resist) bleach,' (b) by the makers of chemical filter- 

 papers, and (c) by the gun-cotton manufacturers, are selected 

 each on an empirical basis and must give way to the ' normal 

 standard,' which has now to be defined. 



The normal pure cotton is clearly a cotton purified from 

 its raw condition by such treatments as attack, and remove its 

 non-cellulose components with the ascertained minimum of action 

 upon the cellulose itself. It is equally evident that none of the 

 technical 'bleaching' processes conform with this specifica- 

 tion. The problem is therefore to devise on a priori grounds 

 a standard process of purification, and to verify the product as 

 a normal standard by the quantitative results of a test reaction 

 or series of reactions. 



We shall avoid a detailed discussion unsuited to the scope 

 of a text-book, and merely state the case and our conclusions. 

 A critical survey of the bleaching processes of the arts shows 

 that the major chemical work of purification is effected by the 

 alkali boil or digestion. From the present point of view these 

 treatments are excessive and too complex in regard to the 

 reactions involved. We therefore propose to substitute the 

 standard laboratory method of boiling with alcoholic sodium 

 hydrate at N/2 strength. (2*0 NaOH per 100 c.c.) 



Starting with a selected cotton sliver or roving, as above 

 described, we found that after treatment with the reagent and 

 thorough washing that the cellulose was very resistant to 

 oxidation. Treated with permanganate (KMnO 4 ) in the cold, 

 it required 3 hours to ' consume ' 075 p.ct. of its weight, repre- 

 senting o'n p.ct. o. As the proportion of residual coloured 

 impurity is fractional, it is a question whether it may not be 



