Action of Iodine upon Sulphides. 159 



bly attacked by the bromide. Argentite, galenite, sphalerite, 

 chalcocite, pyrrhotite, pyrite, and chalcopyrite, are attacked 

 in the cold, with or without liberation of sulphuretted hydro- 

 gen. Molybdenite resists this mixture of reagents, as well 

 as the others previously mentioned. 



In studying the behavior of minerals with organic acids, 

 we obtained results which were embodied in a Table* exhib- 

 iting the eleven groups into which minerals are divided by 

 the action of citric acid alone and with reagents. We are 

 now able to add a twelfth group, viz : " minerals decomposed 

 by heating with citric acid [and potassium iodide," and to 

 transfer thereto, from the list of" minerals not decomposed by 

 the above reagents," four species — cinnabar, magnetite, hema- 

 tite, and franklinite. 



Thus of the ninety minerals whose behavior with organic 

 acids and reagents has been examined, only nine resist these 

 methods of attack. 



Trinity College, Hartford, Conn. 



* Aim. N. Y. Acad. Sci., Vol. I, p. 30. 



