io H. E. Williams — Action of Neutral Salts on Cellulose 



other soluble salts, a number of which have been examined 

 in this manner. Both calcium chloride, and magnesium 

 chloride solution when concentrated to the required viscosity 

 have too great a heat of dilution to dissolve cellulose. 

 Additions therefore which lower the heat of dilution, and 

 either increase, or do not lower the viscosity should convert 

 these solutions into cellulose solvents. This may be accom- 

 plished by dissolving mercuric chloride in these solutions, to 

 form the double calcium mercuric chloride, and the magne- 

 sium mercuric chloride respectively. By this means the 

 viscosity is increased and the heat of dilution greatly reduced, 

 and the concentrated solution of either of these two double 

 salts dissolves cellulose. 



It may here be remarked that the figures given above 

 refer only to neutral solutions, but if the solutions are made 

 acid by a weak acid such as acetic acid, the cellulose is more 

 readily dissolved, and in much greater amounts. If, how- 

 ever, the solution is made alkaline, no solution of the cellulose 

 takes place ; for example, if the solution of the calcium 

 thiocyanate is made basic with a little calcium hydroxide, or 

 the strontium salt solution with strontium hydroxide, the 

 solvent action on the cellulose is entirely arrested ; this is true 

 for all the thiocyanates, and probably also for all salt 

 solutions. 



The concentrated solution of the calcium thiocyanate, 

 which has been more deeply studied than the other salts, 

 not only dissolves cellulose but also dissolves acetyl-cellulose, 

 natural silk, and gelatine; but has no action on wool. The 

 hydroxides of calcium, lead, zinc, cadmium, cobalt, nickel, 

 ferric iron, and stannic tin are all soluble in the concentrated 

 solution. Both the stannic and the ferric hydroxides only 

 begin to dissolve when the thiocyanate solution is concen- 

 trated until the composition of the solution corresponds with 

 the liquid hydrate Ca(CNS) 2 ioH 2 0. This is the lowest con- 

 centration that will dissolve cellulose. The curves represent- 

 ing the percentage of these hydroxides dissolved in the cold 

 for different concentrations of the calcium thiocyanate solution 

 are given in Fig. 5, where it will be noticed that they all take 

 a sharp upward bend from the point where the composition 

 of the solution corresponds approximatelv to the formula 

 Ca(CNS) 2 ioH 2 0. 



That these hydroxides pass into colloidal solution is shown 

 by the colour of the ferric hydroxide solution which is deep 

 brown, showing no trace of the red colour of ferric thio- 

 cyanate. All these hydroxides are completely precipitated on 

 dilution. 



