Experimental and Applied 249 



suitable salts of the heavy metals, and the cellulose xanthate of the 

 metals prepared. 



Cellulose is regenerated from the solution in various ways which 

 may be practised by the student : (a) the solution may be set aside 

 in any suitable vessel for some days ; (b] it may be heated at 80- 

 90 in a water bath ; (c) it may be spread upon a glass plate or 

 other surface, dried at 60 C., and finally heated for some minutes 

 at 100 C. 



The masses or films obtained are washed to remove the alka- 

 line by-products ; and the cellulose bleached, if necessary, by treat- 

 ment with sodium hypochlorite in dilute solution (0-5-1-0 p.ct. 

 NaOCl). Of the special uses of the solution in the laboratory, the 

 following may be particularised : 



(1) In Microscopic Work. In preparing fibres for cutting in 

 cross section, they may be worked up with the viscous solution into 

 a strand or pencil, the cellulose being regenerated spontaneously or 

 otherwise. Such a strand may be cut with or without a microtome, 

 or may be further ' embedded ' in cellulose by submerging it in the 

 viscous solution and coagulating. In some cases the crude solution 

 may be used ; in others the solution should be previously dis- 

 colourised (and neutralised) by treatment with sulphurous acid. 



(2) In diffusion experiments (osmosis) the regenerated cellulose 

 is of use in the preparation of membranes or diaphragms, the 

 cellulose being either used alone, or a compound diaphragm may 

 be made by coating paper or cloth with the thick solution, and 

 'fixing' the cellulose by any of the methods described. 



Important results may be expected from a study of osmotic 

 transmission through this form of cellulose. The passage of 

 crystalloids through the cellulose, especially in its hydrated forms, 

 appears to be exceptionally rapid. 



Theoretical Notes. Determinations have been made in which 

 known weights of pure cotton cellulose have been dissolved as 

 thiocarbonate, the cellulose regenerated, spontaneously and in 

 other ways, then carefully purified and weighed. The cellulose 

 recovered shows a slight increase upon the original. It may be 

 taken, therefore, that the molecule undergoes no permanent dis- 

 aggregation under the treatment, and it is even probable that the 

 cellulose maintains a high molecular weight in solution. In con- 

 trast to its behaviour under the severe alkaline treatment, it has 



