Manchester Memoirs, Vol. Ixv. (1921), Xo. 12 3 



viscosity, and clearly indicates some relationship between a 

 high viscosity of the salt solution and the property of dis- 

 solving cellulose. 



A further examination of these cellulose solvents revealed 

 the fact that not one of them dissolved the cellulose until the 

 boiling point of the concentrated solution rose to 133 — 134 C. 

 or over. This fact is strikingly shown by the solutions of 

 the strontium and manganese thiocyanate which are more 

 viscous than the calcium salt at the concentration at which 

 the latter dissolves cellulose, yet neither of these salt solutions 

 becomes a cellulose solvent until concentrated to the boiling 

 point of 1 33 C. This point would seem to explain the non- 

 solvent action of the aluminium thiocyanate solution, the most 

 concentrated solution of which did not boil above 121 ° C. 

 under atmospheric pressure. 



At this stage a very large number of the solutions of the 

 thiocyanates and double thiocyanates were examined, and the 

 viscosity of the solutions at various concentrations determined. 

 Calcium chloride, a very soluble salt and one with a viscous 

 solution, was also examined in this manner. The figures thus 

 obtained were then plotted against the corresponding boiling 

 points of the solutions. 



As no solution of these salts was so far known which 

 dissolved cellulose under a concentration corresponding with 

 a boiling point of 133 C, this figure was taken as the 

 minimum boiling point of a solution for a cellulose solvent; 

 and also as not one of these solutions, even those boiling 

 above 133 C, was a cellulose solvent unless the solution had 

 a viscosity at ioo° C. of at least 3.3 times that of water at 

 20 C, these two points were taken as the lower limits of 

 these properties in the solvent action of these solutions on 

 cellulose. On these facts it was temporarily assumed that 

 before an aqueous salt solution could dissolve cellulose, it 

 must have a boiling point of 133 C. or over, and a viscosity 

 at ioo° C. of 3.3 times that of water at 20 C. 



In Fig. 1 the reason for fixing these two lower limits is 

 very clearly shown, particularly by the lithium, strontium, 

 barium-manganese BaMn [CNS] 4 , and cerous thiocyanate, 

 for the last three of these have a much greater viscosity than 

 calcium thiocyanate of cellulose solvent strength, vet they do 

 not become solvents unless concentrated until the boiling 

 point of the solutions rises to 133 C. On the other hand 

 lithium thiocyanate solution does not attain the necessary 

 viscosity until the boiling point rises to 165 ° C, at which 

 concentration it becomes a cellulose solvent. 



