Organic Acids in the Examination of Minerals. 15 



All carbonates and phosphates are decomposed by citric 



acid. 

 The sulphides are very unequally attacked ; — two resist the 

 solvents, three yield only to the iodo-citric mixture, 

 twenty-two only to the nitro-citric mixture, and ten 

 are attacked by the acid alone. The oxides and anhy- 

 drous silicates are very unequally attacked. 

 The hydrous silicates are (with one or two exceptions) de- 

 composed by citric acid alone. 

 {b.) An examination of the influence of the basic constituents 

 Oil the solubility discloses the following points. 



All the copper minerals are soluble in one or more of the 



solvents. 

 All the manganese minerals are decomposed, — the sulphide 



and the silicates with great facility. 

 All the lead minerals are decomposed by citric acid alone. 

 In some cases the presence of lead would seem to ren- 

 der a mineral easily broken uj) ; this is marked in the 

 case of the sulphides, which, as we have seen, are very 

 unequally attacked ; — thus selenide of lead is attacked 

 and selenide of mercury is not ; sulphide of lead is 

 attacked, while sulphide of silver is not. The minerals 

 jamesonite, bournonite, and boulangerite (containing 

 lead) are attacked, while the closely allied species ste- 

 phanite, tennantite, polybasite, proustite, berthierite, 

 etc. (devoid of lead) are not decomposed. 

 These facts may possibly point to a connection between 

 chemical constitution and solubility, peculiar to the reagent 

 employed ; but we offer the suggestion with diffidence, OAving 

 to the limited number of facts on which to base generalizations. 

 Moreover we find that the results obtained by the prolonged action 

 of citric acid on minerals (10 to 30 days), differ greatly from those 

 here recorded. To this we shall return at a subsequent period. 

 In conclusion, we beg leave to remind our readers that the 

 immediate object in v^iew, as was stated at length in our first 

 paper, is the practical application of these methods to the ex- 

 amination of minerals in the field. 



Trinity College, Hartford, Conn. 



