370 



Allen and Crenshaw — Sulphides of Zinc, 



The facts may be clearly presented by means of a triangular 

 diagram, From an inspection of which we can see the relation 

 of the solid phases to the composition of the solutions out of 

 which they crystallize, but it must be understood that the 

 phases do not represent equilibrium relations, though the rela- 

 tions are constant. The diagram (fig. 5) refers only to 10 



Fig. 5. 



H,0 



Na 2 Si,0 3 .5H 2 



Fig. 5. The action of sodium thiosulphate on mercuric chloride in 

 solutions of varying composition. 



per cent solutions. All the solutions plotted contain a con- 

 stant quantity of sodium chloride (2 g. per 100 cc ), it having 

 been found that the decomposition of sodium mercuric chloride 

 proceeds much more slowly than that of mercuric chloride and 

 better crystals appear to be obtained by the use of it. 



1. All solutions lying in the field above the line 1,11 precipi- 

 tate white mercuric chlorosulphide, HgCl 2 .2HgS. It will be 

 observed that the line 1,11 includes all solutions in which the 

 ratio of HetCL to Na„S„0„ is as 3 mol : 2 mol while all solu- 



