Cadmium, and Mercury. 



377 



able in specific gravity, 

 of this property at 25° : 



I II 



7-221 7*215 



The following are the determinations 



in 



7-179 



IV 

 7-199 



Average 

 7-20 



The refractive indices in lithium light were found to be 2"58 

 and 2*82 (Merwin). There can be no doubt that this is a new 

 form of mercuric sulphide with properties quite different from 



Fig. 6. 



605 c 



585 c 



565° 



545 c 



Time. 



Fig. 6. Sublimation curves of ff-HgS. 



cinnabar, though the color of the powder is not to be distin- 

 guished from ordinary vermilion. 



Relation of the mercuric sulphides to one another. 



Like zinc and cadmium sulphides, mercuric sulphide volatil- 

 izes without melting at atmospheric pressure. The pressure 

 reaches one atmosphere at about 580°, as may be seen from the 

 curves in fig. 6. In these experiments the sulphide was heated 

 in an atmosphere of hydrogen sulphide. Cinnabar is the stable 

 form over the whole temperature range up to the volatilization 

 point. That the other two forms are both monotropic is proved 

 by the following facts. At 100° both a'-HgS and /3'-HgS are 

 changed into cinnabar with ammonium sulphide solutioiCwhile 

 at 200° the same change takes place very slowly in sealed tubes 

 with 30 per cent sulphuric acid. At' 400°, "450°, 500°, and 

 550°, both are transformed into cinnabar when heated alone in 

 evacuated glass tubes. The heating was done in a stirred 

 nitrate bath. Table XI shows the results. 



