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. 



{b) Amnioniacal 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 CF.LLULOSE. 



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, logo; 

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



