8 Prof. J. Joly on the 



The Table shows that sulphur is generally liberated from 

 the metallic sulphides between 440° and 480°. Certain of the 

 minerals examined, i. e. hauerite, kilbrickenite. and zinkenite, 

 liberated a part of their sulphur at a lower temperature. 

 Generally, this sulphur was little more than a trace. In the 

 case of the kilbrickenite, however, the low-temperature sub- 

 limate of sulphur amounted to 5 per cent, by weight of the 

 mineral after prolonged heating at 185°. This is nearly one- 

 third of the sulphur present. 



Tellureum. 



Only 7 tellurideshad been examined at the time of writing 

 the first paper. Those few results appeared to indicate that 

 the tellurides were divisible into groups according as the 

 molecule is of the structure RTe or RTe 2 . This view is 

 sustained by the additional observations now available. 



I may recall that the presence of tellurium may be indi- 

 cated by a black sublimate, TeO, which is peculiar to 

 tellurides breaking up at a relatively low temperature (about 

 500°) or by a white sublimate which is only formed at a 

 higher but rather variable temperature : — G00° to 900°. The 

 white sublimate has the composition Te0 2 . Tellurides which 

 first break up at the higher temperature only show the white 

 sublimate. Those which become unstable at the lower 

 temperature give the black sublimate, and if the tempe- 

 rature be then raised, the white sublimate also. The more 

 stable tellurides possess the structure RTe ; the less stable 

 the structure RTe 2 , or RTe 3 . Hence these two classes may be 

 at once identified by the colour of the sublimate first given 

 off on gradually heating them on the apophorometer. 



1, 



Attaite. 

 Hessite. 

 Petzite. 



PbTe. 



Ag 2 Te. 



(AuAg)Te. 



T. 



A.BLE IV. 



ETe. 





.. Te0 2 



5! 



t°. 



850 



o 







8<>0 



••; 



Loc. ? 





710 



4 



Altai 





flOO 



5 







8?0 



tf. 



Sardinsky Mine, 



Altai .... 



930 

 750 











