Organic Acids in tlm Examination of Minerals. 13 



mite, psendomalachite, wavellite, pharmacosiderite, tor- 

 bernito, autnnite, nlcxite, cryptomorpliite, and broch- 

 antifce. Wulfenitc and crocoite are strongly attacked 

 on boiling, the latter yielding a green solution, owing 

 to the reducing action of the organic acid on the 

 chromic acid. 

 Columbite and wolframite are attacked by the iodo-citric 



mixture, at least so far as partially to dissolve the iron which 



forms one of their constituents. 



Iliibnerite is attacked by the nitro-citric mixture; while scheel- 



ite, barite, celestite, anhydrite, and graphite, resist completely 



these methods of attack. 



Native Elements. — In onr first paper we called attention to 



the solvent power of the nitro-citric mixture, as shown by the 



fact that it dissolves metallic copper, silver, lead, tin, bismuth, 



and antimony, besides iron, zinc, and magnesinm, (20); to this 



list we now add arsenicnm and mercury. 



Tabulation of Eesults. 



34. In paragraph (22) Ave gave a table showing the behavior 

 of ninety minerals with citric acid and other reagents, arranged 

 nnder eleven heads, viz. :— 



A. Minerals which dissolve in cold citric acid withont evo- 



lution of gas. 



B. Minerals which dissolve in cold citric acid with libera- 



tion of carbonic anhydride. 

 C Minerals which are decomposed by cold citric acid with 

 evolntion of sulphuretted hydrogen. 



D. Minerals which dissolve in hot citric acid withont evo- 



lution of gas. 



E. Minerals which dissolve in hot citric acid with liberation 



of carbonic anhydride. 



F. Minerals which are decomposed by hot citric acid with 



evolution of sulphuretted hydrogen. 



G. Minerals which are decomposed by hot citric acid with 



formation of gelatinous silica. 

 H. Minerals which are decomposed by hot citric acid with 

 separation of slimy silica. 



