B44 



Allen and Crenshaw — Sulphides of Zinc, 



It appears from the above data that the specific gravities of 

 sphalerite and wurtzite of identical composition are nearly the 

 same, but that of wurtzite is very slightly lower. 



Enantiotropic relation between Sphalerite and Wurtzite. 



If sphalerite is heated to a temperature of about 1100° and 

 cooled with moderate rapidity, i. e., to 100° inside of two hours, 

 microscopic examination shows that it is completely trans- 

 formed into wurtzite.* The heating curve, however, shows no 

 break to indicate that aii} r heat chauge has accompanied the trans- 

 formation. A very careful test of this point was made as follows :f 



Fig. 1. 



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Fig. 1. Heating curves for sphalerite and wurtzite in the vicinity of 

 the inversion point, x x Sphalerite, O O Wurtzite. 



Two small cylindrical crucibles, one containing 10 g. sphalerite 

 and the other 10 g. wurtzite, each provided with a calibrated 

 thermoelement, were heated side by side in the same furnace, 

 the temperature of the two elements being read alternately 

 every half-minute. By reference to the curves in fig. 1, it is 

 seen that those of the first pair are practically parallel ; those 

 of the second pair are virtually identical, i. e., the temperature 

 of the two crucibles, by reason of their position in the furnace, 

 w r as a little closer together in the second case. Neither pair 



* J. Weber heated small plates of sjmalerite in a Bunsen flame and cooled 

 quickly. He found they had become anisotropic. Zs. Kryst., xliv, 212, 1908. 

 Biltz expressed the opinion that sphalerite might change to wurtzite with- 

 out sublimation. Zs. anorg. Ch., lix, 273, 1908. 



f See W. P. White, this Journal, xxviii, 488, 1909. 



