CELLULOSE 209 



verted into a gelatinous hydrate which, after prolonged treat- 

 ment, goes into solution. 



A solution of 6 parts of zinc chloride in 10 parts of water 

 heated to 60-100° is thoroughly stirred up with i part of 

 cellulose, and then digested for some time at a gentle heat. 

 When the cellulose is gelatinized, its solution is completed by 

 heating over a boiling water bath, and adding water from 

 time to time to replace that lost by evaporation. 



Two other salt solutions are known which dissolve cellu- 

 lose : — 



{a) Zinc Chloride and Hydrochloric Acid. — A solution of 

 zinc chloride in twice its weight of hydrochloric acid dissolves 

 cellulose rapidly in the cold. 



[h] Ammoniacal Cupric Oxide [Schweitzer' s Reagent). — The 

 solution is most conveniently prepared by drawing a current 

 of air through a Wolff bottle containing o-88o ammonia and 

 some copper turnings, until a deep blue solution is obtained. 

 Cellulose dissolves in this solvent and on the addition of acid 

 is reprecipitated. 



ACTION OF VARIOUS CHEMICALS ON CELLULOSE. 



I. Alkalis. — Solutions of caustic soda of 1-2 per cent 

 strength have no action on cellulose at temperatures con- 

 siderably above 100°. 



When cotton fibres are immersed in a 17-5 per cent solution 

 of caustic soda they shorten, swell up, and the lumen becomes 

 obliterated ; the physical process of swelling is accompanied 

 by a chemical change involving the formation of an unstable 

 sodium compound CgHgOgNa ; on washing with water the 

 sodium is removed, but the recovered cellulose has, as a result 

 of its swelling, acquired a greater affinity for dyes. This 

 observation was first made by Mercer in 1844 and technically 

 exploited by him for dyeing cotton. Later, in 1890, it was 

 discovered by Lowe that if the alkali treatment is carried out 

 while the cotton was under tension the fibres acquired a lustre, 

 a process known as mercerization. 



When fused at 200-300° with a mixture of sodium and 



14 



