Cadmium, and Mercury. 361 



naturally not well developed in the mass, though there were 

 some well-formed prisms which had evidently crystallized 

 direct from the vapor. The whole product was identified by 

 its optical properties as greenockite. This mineral has been 

 formed* by others at high temperatures and its volatility has 

 been noted. f Heating and cooling curves were determined 

 on the product crystallized as above, the same apparatus being 

 used. No break was found anywhere from ordinary temper- 

 ature to 1000° to indicate any physical transformation what- 

 ever. These results, however, can not safely be regarded as 

 conclusive, because the effects which accompany definite phys- 

 ical changes are sometimes too small to be thus detected. 

 Furthermore, unstable forms are often capable of existence 

 under certain conditions, while they would not be found under 

 circumstances like those described above. 



Lorenz^: states that he obtained beautiful crystals of cadmium 

 sulphide by vaporizing metallic cadmium in a strong current 

 of hydrogen sulphide. The preparation was examined by 

 Prof. Groth, who found in it simple crystals of greenockite, 

 and also twinned forms in large number, which he regarded 

 as monoclinic. Lorenz accounted for two crystal forms in the 

 same preparation by the supposition that the temperature 

 varied greatly in different parts of the mass. We made two 

 preparations by this method. The largest crystals, w T hich sur- 

 passed 20 mm in length, were made by heating in a resistance 

 furnace a porcelain tube which enclosed the boat containing 

 the metal. When the boiling point of cadmium was reached 

 the galvanometer indicated a temperature of 780°, wdrich held 

 constant about ten minutes. After heating half an hour 

 longer, during which the hydrogen sulphide was passed in 

 rapidly, the furnace was cooled down. The product so 

 obtained and also a previous one made by heating with an 

 ordinary blast lamp, contained many twinned crystals, as well 

 as simple prisms of greenockite. It would be easy to mistake 

 these forms for monoclinic twins, but a careful study of them 

 by Dr. Merwin (Microscopic Study) has shown conclusively 

 that they are hexagonal, twinned after two different pyra- 

 mids. 



The cadmium which we used in the formation of the 

 sulphide was of known composition ; the total impurities were 

 Pb = '086 per cent, Fe = # 002 per cent. The sulphide was, 



*Deville & Troost obtained it by beating tbe amorpbous sulpbide to a 

 white beat in a current of bydrogen ; also by heating together CdSO.4, BaS 

 and CaF 2 in equal quantities : C. B., lii, 920, 1861. Mourlot sublimed cad- 

 mium sulphide in the arc furnace ; C. B., cxxiii, 54, 1896. 



f Biltz states that greenockite begins to sublime about 980° ; Zs. anorg. 

 Ch., lix, 273, 1908. 



\ Loc. cit. 



