Cadmium, and Mercury. 363 



by the probable presence of cadmium sulphate in the crystals, 

 a hypothesis which is in accord with the well known tendency 

 of this substance to occlude salts from the solution in which it 

 is precipitated. 



In other experiments carried out in a similar way, the crys- 

 tals of the product were smaller. When amorphous cadmium 

 sulphide was heated in a sealed tube with 30 per cent sulphuric 

 acid at 200° for two days, the product consisted of sphernlitic 

 aggregations of small doubly reacting prisms. Again hydro- 

 gen sulphide was passed into a boiling solution which contained 

 1 g. CdS0 4 .8/3H 2 in 50 cc. 30 % H 2 S0 4 . After the air had been 

 entirely replaced from the flask, the latter was connected with 

 the hydrogen sulphide generator and allowed to cool. Most 

 of the product crystallized during the cooling. It consisted of 

 spheroidal lumps of amorphous material shot through with 

 doubly refracting needles. The crystals of the two last-named 

 products showed parallel extinction though they were too 

 small for a determination of the refractive index. 



We also prepared crystalline cadmium sulphide by the 

 method of Geitner,* which consists in heating the metal with 

 sulphurous acid in sealed tubes. Cadmium chips were sealed 

 up in a tube of Jena combustion glass with a solution of 

 sulphurous acid, saturated at room temperature. The tube 

 was heated to 200° for two days. The crystals of the product 

 were of such size that it was possible to determine the crystal 

 system. They were hexagonal. 



Cadmium sulphide from alkaline solutions. 



If cadmium sulphide behaves like zinc sulphide, its closest 

 analogue, we should expect a different product to crystallize 

 from alkaline solutions, perhaps a regular form similar to 

 sphalerite. In the first place we repeated Stanek'sf experi- 

 ments — heating the amorphous sulphide with excess of colorless 

 ammonium sulphide in a sealed tube to 150°-200°. We used 

 in our experiment 1/2 g. OdS0 4 . 8/3 H 2 with excess of color- 

 less ammonium sulphide, prepared from concentrated ammonia. 

 The sealed tube was heated three days at 200°. Microscopic 

 examination of the product showed that it was all crystallized 

 in doubly refracting needles showing •parallel extinction. In 

 a repetition of this experiment, larger crystals were obtained ; 

 they were well-formed hemimorphic prisms, undoubtedly gren- 

 ockite. On the other hand, no crystalline product was obtained 

 with sodium or potassium sulphides. Orange-colored sulphide 

 of cadmium remained unchanged, when heated at 200° for two 

 clays with dilute solutions of potassium (3 - 5 per cent) or sodium 



*Liebig's Ann., cxxix, 350. J. B. Ch., 1864, 140. 

 fZs. anorg. Ch., xvii, 1898. 



