Manchester Memoirs, Vol. Ixv. (192 1), No. 12 9 



Additions to the potassium salt solutions to increase its 

 viscosity do not, however, produce cellulose solvents, though 

 higher boiling points and viscosity results ; for all these 

 mixtures so far examined have, unlike the corresponding 

 sodium thiocyanate, a large negative heat of dilution. 



Again lithium thiocyanate solution does not become a 

 solvent for cellulose until concentrated to a boiling point of 

 165 C, the viscosity being too low for all concentrations 

 below this boiling point. If the conclusions arrived at above 

 are correct, it should be possible to lower the concentration 

 at which the solution becomes a cellulose solvent by additions, 

 which, while not diminishing its heat of dilution, will yet at 

 the same time increase its viscosity. This may be accom- 

 plished by a variety of substances, such as other thiocyanates 

 of characteristic viscous solutions as for example the man- 

 ganese, calcium or aluminium thiocyanate. The addition, 

 however, need not be a thiocyanate for thiourea, hexamethy- 

 lenetramine, or diycandiamide may be added with like effect. 

 These results are illustrated by curves given in Fig. 4. 



It is interesting to note that each of these solutions 

 becomes a cellulose solvent at the particular concentration 

 represented by the point where the boiling point viscosity 

 curve cuts into the solution area. Lithium thiocyanate solu- 

 tion does not dissolve cellulose until it is concentrated to a 

 boiling point of 165 C; but when the viscosity of the solu- 

 tion is increased by additions of other soluble compounds, a 

 cellulose solvent mav be obtained boiling 30 C. lower. Each 

 of these solutions has a positive heat of dilution when concen- 

 trated. 



It is thus seen that whatever the explanation may be 

 there is a definite connection between the boiling" point, the 

 viscosity and the heat of dilution of a solution of a neutral 

 salt, and its solvent power for cellulose. This relationship 

 has been very strikingly demonstrated in the course of this 

 work on the thiocyanates, for every thiocyanate either singly, 

 or in conjunction with one or more other thiocyanate solu- 

 tions, has been converted into a cellulose solvent, although 

 the components of these mixtures may not of themselves 

 dissolve cellulose. In each case, however, it has been neces- 

 sary to bring the viscosity, heat of dilution, and boiling point 

 within the limits stated above, either by concentrating the 

 solution, or by additions of other thiocyanates either soluble 

 or insoluble — the latter being soluble in the concentrated 

 solutions of the soluble thiocyanates. 



These facts apply not only to the thiocyanates, but to all 



