350 Allen and Crenshaw — Sulphides of Zinc, 



hours crystallized from the same solvent in still larger crystals. 

 The temperature in nearly all these experiments was very near 

 the melting point of sodium chloride, slightly ahove 800°. 

 Schneider* formed crystalline zinc sulphide by heating 1 part 

 of pure dry amorphous zinc sulphide with 12 parts potassium 

 carbonate and 12 parts sulphur. A repetition of this experi- 

 ment confirmed Schneider's statement. Larger crystals than 

 those from sodium chloride were obtained in this way at about 

 400°. Both dodecahedrons and tetrahedrons were observed. 



Thermal behavior of ZnS above its inversion point. 



Cussak f states that zinc sulphide melts at 1064°. No other 

 investigator has ever observed the melting of zinc sulphide, 

 though several have, obtained wurtzite as a sublimation pro- 

 duct. :]: The results of Hautefeuille are especially interesting 

 since he obtained well-characterized hemimorphic crystals like 

 those of nature by subliming zinc sulphide in a bed of alumina. 

 We found zinc sulphide volatile enough at about 1000° to form 

 small crystals of wurtzite in a few hours. Several grams were 

 sublimed in well-formed crystals of considerable size between 

 1200° and 1300°. We observed no melting under any circum- 

 stances at atmospheric pressure. The experiment was tried of 

 dipping a tube containing zinc sulphide quickly into a furnace 

 heated to 1550°. It was thought that if this temperature were 

 above the melting point, deorientation might go on faster than 

 volatilization, but no certain indication of melting was found. 



Zinc sulphide from aqueous solutions. 



It has been shown in the foregoing pages that zinc sulphide 

 may exist in two enantiotropic forms ; /3-ZnS, or sphalerite, 

 stable below 1020°, and a-ZnS, or wurtzite, stable above 1020°. 

 Nevertheless the latter as well as the former may be crystal- 

 lized at comparatively low temperatures from aqueous solutions, 

 and the necessary conditions for the formation of each are of 

 the highest interest to chemical geology. Zinc sulphide is sur- 

 prisingly difficult to crystallize below 200° and it is safe to say 

 neither sphalerite nor wurtzite has been obtained heretofore in 

 the wet way. 



Sphalerite from aqueous solutions. 



Several investigators claimed to have obtained sphalerite 

 from water solutions. Baubigny § is said to have formed 



* Jour, prakt. Chem. (2), viii, 33, 1874. 



+ N". J. Mill. 1899, I, Keferate 196. 



% Deville and Troost, C. E., lii, 920, 1861. Sidot, ibid., lxii, 999, 1866 ; lxiii, 

 188, 1866. Hautefeuille, ibid., xciii, 824, 1881. Mourlot, ibid., cxxiii, 54, 

 1896. Biltz, loc. cit. 



§ Fouquee et Levy, Synthese des Min. et Koches, Paris, 1882, 298. 



