Manchester Memoirs, Vol. Ixv. (192 1), No. 12 5 



tions, and the molecular heat of dilution plotted against the 

 boiling points. These determinations were not of high 

 accuracy owing to the difficulties of such operations in a 

 works laboratory ; but the results obtained were sufficient to 

 give the necessary explanation. It may be of interest here to 

 remark that early in this work it was found that to dilute the 

 solutions of the different salts with the same quantity of water, 

 as in the usual practice, gave results that were without definite 

 meaning. On gradually diluting many of these concentrated 

 solutions an evolution of heat is at first observed up to a 

 point ; further dilution beyond that point results in an absorp- 

 tion of heat. With concentrated calcium thiocyanate solution 

 heat is evolved on gradual dilution until the molecular ratio 

 of salt and water is 1 120; further dilution beyond this point 

 results in an absorption of heat. With strontium thiocyanate 

 solution this point is reached at the ratio of 1 : 18 ; and calcium 

 chloride solution at about 1 :3c In order to obtain the true 

 molecular heat of dilution it is necessary first to determine 

 this ratio for the particular salt under observation, and to 

 determine the heat evolved by diluting the concentrated 

 solution to this point. 



The results obtained in this manner showed that the 

 concentrated calcium chloride solution has a very high heat 

 of dilution, much higher than that of any of the other salts 

 examined ; whereas the potassium-manganese thiocyanate 

 solution has a large negative heat of dilution. The former 

 solution therefore at this concentration would have too strong 

 a dehydrating action to dissolve cellulose, but the latter would 

 have neither a dehydrating nor a hydrating action. 



As calcium chloride with so large a heat of dilution was 

 a non-solvent for cellulose, it was thought possible that if the 

 calcium thiocyanate solution could be made concentrated 

 enough, a point should be reached when its heat of dilution 

 would be so great that it would cease to be a cellulose solvent. 

 Experimental evidence showed this to be true for a solution 

 concentrated to a boiling point of 150 C. and over. At this 

 concentration no cellulose was dissolved even after heating 

 for some time, though the fibres appeared highly swollen. 

 The addition of a very small amount of water, sufficient to 

 drop the boiling point of the solution to 148 C., caused the 

 cellulose to dissolve rapidly. 



In a similar manner strontium thiocyanate solution of 

 boiling point 140 C. and upwards proved to be a non-solvent 

 for cellulose, and magnesium thiocyanate solution of boiling 

 point 150 C. and above. Slight dilution to reduce the boiling 



