Cadmium, and Mercury. 369 



meters of strong sodium sulphide solution and allowed to stand 

 for a short time, the black material is completely removed. 

 After the addition of a little water the product is filtered and 

 then washed with more and more dilute sodium sulphide solu- 

 tion, so as to prevent the precipitation of the dissolved HgS, 

 and finally with water. This treatment would also remove 

 free sulphur in case any had formed by dissociation of 

 some HgS, during the process of sublimation. The product is 

 now digested with warm dilute nitric acid to remove any free 

 mercury,* washed with water, alcohol and ether and thor- 

 oughly dried in a vacuum desiccator containing sulphuric acid. 

 This product showed, under the microscope, all the properties 

 of cinnabar in much larger crystals than the original powder. 

 Table IX shows the specific gravities of various preparations 

 of cinnabar before and after sublimation. 



Table IX. 

 Specific gravities of cinnabar at 25°. 

 Sublimed and purified. Vermilion powder. 



Prep. I. Prep. II. Prep. I. Prep. II. 



8-200 8-198 8-191 8-186 



8-198 • 8-190 



8-188 



8-188 



8-187 



Careful experiments have shown that the vermilion powder 



contains a little carbonaceous matter as well as about 0-02 per 



cent of sulphide of iron. The sublimed product is purer and 



its constants are to be regarded as more reliable. 



m, j -j. x- a ■ v Mineral at 25° n -, ■, 



Ihe density of the pure cinnabar, — = — would be 



J l ' Water at 4° 



therefore 8-176. The lower refractive index directly measured 



is, (o Li = 2-85. The double refraction is 0*35, making the 



higher index e Li = 3 - 20. (See microscopic part.) 



The behavior of mercuric salts with soluble thiosulphates. 



Before going further it will be well to explain the interest- 

 ing chemical behavior of mercuric salts with soluble thiosul- 

 phates, which is somewhat complicated. Three solid phases 

 may be obtained from such solutions which contain from — 

 25 per cent by weight of total salts. For the purposes of this 

 investigation it was thought unwise to carry the concentrations 

 farther. It was found that the chemical reactions depended 

 entirely on the ratios between the salts, while the phase which 

 separated was also dependent on the degree of dilution. 



* A very high specific gravity (8 - 7) of one product prepared without digest- 

 ing with nitric acid was strong indication of the presence of mercury. 



