8 Cellulose 



Solutions of Cellulose. Cellulose is insoluble in all 

 simple solvents, water included. In presence of certain metallic 

 compounds, however, it combines rapidly with water, forming 

 the gelatinous hydrates just described, which finally disappear 

 in solution in the water. Of these solvents of cellulose the 

 simplest is (i) ZINC CHLORIDE IN CONCENTRATED AQUEOUS 

 SOLUTION (40 p.ct. ZnCl 2 ). The solution process requires 

 the aid of heat (60-100), and may be carried out as follows : 

 4-6 pts. ZnCl. 2 are dissolved in 6-10 pts. water and one pt. 

 cellulose (cotton) stirred in till evenly moistened. The 

 mixture is set aside to digest at a gentle heat. When the 

 cellulose is gelatinised the solution is completed by exposure 

 to water-bath heat, stirring from time to time and renewing 

 the water which evaporates. In this way, a homogeneous 

 syrup is obtained. This solution is employed in the arts for 

 making cellulose threads or filaments which are carbonised 

 for use in the incandescent electric lamp ; the ' carbon ' so 

 obtained having a sufficient resistance to mechanical strain with 

 the suitable degree of electric conductivity (resistance) for the 

 requirements of the lamp. In preparing the cellulose thread 

 the viscous solution is allowed to flow from a narrow orifice 

 into alcohol which precipitates a hydrate a hydrated cellulose- 

 zinc-oxide of sufficient tenacity for manipulation as a thread. 

 It is freed from zinc oxide by digestion in dilute hydrochloric 

 acid and copious washing. The cellulose zinc chloride solu- 

 tion is also precipitated by water, retaining a much larger pro- 

 portion of water (of hydration). After thorough washing and 

 drying a product is obtained retaining from 18-25 P- ct * 

 ZnO ; the variation in the proportion of ZnO to cellulose, no 

 doubt, corresponding with variations in molecular weight of 

 the latter, and these depending upon the molecular condition 

 of the original cellulose and the conditions of the solution 

 process. 



