The Typical Cellulose and the Cellulose Group 9 



(2) ZINC CHLORIDE AND HYDROCHLORIC ACID. If the 

 ZnCl 2 be dissolved in twice its weight of aqueous hydrochloric 

 acid (40 p.ct. HC1) a solution is obtained which dissolves 

 cellulose rapidly in the cold. This alternative process has 

 certain advantages over the preceding, and is useful in labora- 

 tory investigations. So far it has received no industrial 

 applications. It is to be noted that the cellulose dissolved in 

 this reagent undergoes a gradual lowering of molecular weight 

 (hydrolysis). 



This process of dissolving cellulose is of value in the investi- 

 gation of fibrous products in the laboratory in cases where an acid 

 solvent is preferable, and where it is necessary to avoid heat. 



If to the solution of pure cotton cellulose in this reagent bromine 

 be added in quantity sufficient to colour the solution, the colour 

 persists for a lengthened period, showing that there is no absorption 

 of the bromine, and that, therefore, there are no C = C groups 

 in the cellulose molecule. With the lignocelluloses (see p. 138), 

 which are also soluble in this reagent, and are known by other 

 reactions to contain C = C groups, there is considerable absorption 

 of bromine. 



It is also noteworthy that if this solution of cellulose be 

 coloured with CrO 3 , it persists for some time in the unreduced 

 state. There cannot, therefore, be any free CO.H groups in the 

 cellulose molecule, and the observation rather throws doubt on the 



c\~v 



existence of such groups in an 'acetal' form CH<^Q^' 



(3) AMMONIACAL CUPRIC OXIDE. The solutions of the 

 cuprammonium compounds generally, in presence of excess of 

 ammonia, attack the celluloses rapidly in the cold, forming a 

 series of gelatinous hydrates which finally pass into solution. 

 The solutions of the pure cuprammonium hydroxide are more 

 active in producing these effects' than the solutions resulting 

 from the decomposition of a copper salt with excess of 

 ammonia. Two methods are in common use for the preparation 

 of these solutions, which should contain : 



