134 THE CARBOHYDRATES 



verted into a gelatinous hydrate which, after prolonged treat- 

 ment, goes into solution. 



A solution of six parts of zinc chloride in ten parts of water 

 heated to 60-100 is thoroughly stirred up with one part of cellu- 

 lose, 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. 



(fr) Ammoniacal cupric oxide (Schweitzer's Reagent). The 

 solution is prepared by adding ammonium chloride and then 

 excess of sodium hydrate to a solution of a cupric salt ; the 

 blue precipitate so obtained is then washed, pressed on a cloth 

 filter, and dissolved in 0*92 ammonia. Cellulose dissolves in 

 this solvent and on the addition of acid is reprecipitated ; this 

 fact is made use of in the preparation of artificial silk. 



ACTION OF VARIOUS CHEMICALS ON CELLULOSE. 



I. Alkalis. Solutions of caustic soda of I to 2 per 

 cent strength have no action on cellulose at temperatures con- 

 siderably above 100. Solutions containing 10 per cent have 

 a curious effect on cotton fibre, causing it to thicken and be- 

 come more cylindrical, and destroying the central canal. This 

 phenomenon was first made use of technically by Mercer, who 

 found that by this means cotton could be made to acquire a 

 gloss resembling that of silk, since the fibre becomes trans- 

 lucent during the contraction. 



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

 potassium hydroxides, cellulose undergoes complete decom- 

 position with the formation of oxalic and acetic acids. 



The so-called alkali cellulose obtained by mercerizing 

 cellulose with about 1 5 per cent caustic soda reacts with carbon 

 disulphide to form xanthogenates ; * these compounds are used 

 in the manufacture of viscose (see below). 



* Cross, Bevan and Beadle: " Ber. deut. chem. Gesells.," 1893, 26, 1090; 

 and Cross and Bevan : " Ber. deut. chem. Gesells.," 1901, 34, 1513. 



