158 Action of Iodine upon Sulphides. 



violence ; and on cooling, the solution deposits white crystals 

 of hydro-potassium oxalate, mixed with scarlet crystals of mer- 

 curic iodide. 



The probable nature of this reaction is shown in the follow- 

 ing equation : ■ 



2H 2 C A + HgS + 2KI=2KHC 2 4 + Hgl 2 + H,S. 



We examined the behavior of a few additional minerals 

 with a mixture of potassium iodide and citric acid, with the 

 results recorded below ; but no special interest seems to be 

 attached to this method of attack. 



Magnetite is decidedly, and franklinite feebly, attacked in 

 the cold, and strongly on heating. Hematite is feebly at- 

 tacked, and chromite not at all. 



Ilausmannite,pi/rolusite, and the other oxides of manganese, 

 being attacked by citric acid alone, .yield, as may be anticipa- 

 ted, deep brown-red solutions colored by the free iodine. 



Angleslte and pyromorphite are completely decomposed in 

 the cold, with formation of a yellow precipitate of plumbic 

 iodide. 



Cuprite is also completely decomposed in the cold, with for- 

 mation of a yellowish-white precipitate of cuprous iodide, and 

 a colorless solution. If, however, heat be applied at the out- 

 set, the same precipitate forms, while the solution is of a blue 

 color. 



We also examined the behavior of natural sulphides with a 

 mixture of citric acid and potassium bromide. The latter 

 does not, however, appear to be so easily decomposed as the 

 iodide, and no characteristic phenomena were observed; nearly 

 all the metallic bromides being soluble in water, no precipi- 

 tates were obtained. In order to avoid repetition, we may 

 briefly summarize the results by stating that, in general, the 

 action of the bromide is less energetic than that of the iodide. 

 Those minerals which yielded only with difficulty to the lat- 

 ter reagent, resist the former even on heating. Cinnabar, 

 whose behavior with the iodide is so remarkable, is but fee- 



