Cadmium, and Mercury. 351 



blende by heating to 80°, in a sealed tube, an acid solution of 

 zinc sulphate, saturated with hydrogen sulphide. We prepared 

 many products in a similar way and none of them ever showed 

 an index of refraction greater than about 2'25, which is charac- 

 teristic of amorphous zinc sulphide. 



Villiers * states that the precipitate from alkaline zinc solu- 

 tions by hydrogen sulphide, though amorphous ordinarily, 

 is crystallized by certain influences, e.g. by the presence of a 

 large excess of ammonium chloride in the solution from which 

 it is precipitated. Heat also transforms the gelatinous precipi- 

 tate into a distinctly granular state, in which, though it does 

 not show any appearance of crystallinity, it is probably cubic 

 because it possesses a decidedly lower solubility than the gela- 

 tinous mass at first formed. Precipitates which we obtained 

 in this way were also amorphous. 



Stanek f believed he had obtained a crystalline product 

 when he heated amorphous zinc sulphide with colorless ammo- 

 nium sulphide to 150° — 200°, in sealed tubes. 



Senarmont \ states that by heating the amorphous sulphide 

 in sealed tubes with hydrogen sulphide under a pressure of 

 several atmospheres he obtained blende. The last-named investi- 

 gators (Stanek and Senarmont) give no proof of their claims 

 except the appearance of the product. Their experiments, 

 repeated by us more than once, gave nothing but amorphous 

 sulphide. JN"o crystal outlines appeared under the microscope, 

 and when the grains were coarse enough to admit of the measure- 

 ment they showed a refractivity of 2 - 2 to 2-3 instead of 2 - 37. 

 Having failed to accomplish our purpose by any methods given 

 in the literature, we experimented with alkali sulphides in 

 sealed tubes with the result that only amorphous products were 

 obtained at first and when the tubes were heated for long 

 periods or at higher temperatures (250° and above) they were 

 so badly attacked, that the method was temporarily abandoned. 



Meanwhile other methods were tried. 

 » 



Action of sodium thiosulphate on Zinc salts. 



Our success with the use of thiosulphate in the preparation 



of the mercuric sulphides gave us some hope that it might 



prove satisfactory here. Sodium thiosulphate in excess shows 



no action on zinc salts in the cold, but on heating to 100° the 



zinc is quantitatively precipitated in dense form, which under 



the microscope appears in spherical aggregations. This is 



amorphous, however. Though in one instance there seemed 



to be slight double refraction as if from wurtzite, the refractive 



index was too low. The principal reaction here, gives rise only 



*C. R., cxx, 189, 498, 1895. fZs. anorg. Ch., xvii, 117, 1898. 



% Ann. Ch. Ph., xxxii, 129, 1851. 



