348 



Allen and Crenshaw — Sulphides of Zinc, 



The impurities in those blendes are all small exeept in V, 

 and we are certainly justified in correcting the gravities for 

 quartz and pyrite in III and V, respectively, since these im- 

 purities are mechanically mixed, The specific volumes plotted 

 in fig. 3 show a nearly rectilinear relation. The dotted line on 

 the plot is drawn through the specific volumes of ZnS and 



Fig. 



1030° 

 1010° 

 990° 

 970° 

 950° 

 930* 

 910° 

 890° 

 870° 

 850° 



























































































































































































































































































\ 









































\ 











































s v 









































\ 











































\ 











































\ 











































\ 











































V 



■. 











































\ 































































































































^ 



\ 



































































































































































































































































5 10 

 Percentage of iron. 



15 



Fig. 2. Influence of iron on the inversion temperature of sphalerite. 



FeS.* If we compare this with the locus of the actual specific 

 volumes of the natural blendes, it is evident that the solution 

 of ferrous sulphide by sphalerite (ZnS) must be attended by a 

 marked expansion. 



For the relation of the indices of refraction of these solu- 

 tions to their composition see microscopic part. 



* See Allen, Crenshaw and Johnston, this Journal, xxxiii, 198, 1912. 



