2 Organic Acids i.ii the JExainination of Minerals. 



Similar renctions with oxalic, tartaric, acetic, and other or- 

 ganic acids, were described in the first paper, but preference is 

 given to citric acid on account of its greater solvent power. 



Minerals belonging to several groups were submitted to these 

 }irocesses, and gave phenomena which may be summarized as 

 follows : 



1st. More or less complete decomposition and solution of 

 oxides, phosphates, etc., without formation of precipi- 

 tates or liberation of gases. 

 2d. Complete solution of carbonates with evolution of car- 

 bonic anhydride. 

 3d. Decomposition of sulphides with evolution of sulphuret- 

 ted hydrogen. 

 4th. Decomposition of sulphides with oxidation of the sul- 

 phur. 

 5th. More or less perfect decomposition of silicates with 



separation of either slimy or gelatinous silica. 

 6tli. Decomposition of certain species by reagents forming 



characteristic precipitates. 

 7th. Wholly negative action. 

 These facts demonstrated that citric acid has a power of de- 

 composing minerals little less than that possessed by hydro- 

 chloric acid, and that this very difference in degree gives the 

 organic acid an advantage over the mineral acid in the determi- 

 nation of species. 



27. This peculiar selective power of citric acid rendered de- 

 sirable a further study of its action on a larger number of mine- 

 rals ; the following list contains the names of the species which 

 have since been submitted to the process named, together with 

 their formulse, condition, and locality. 



Within the groups, — I, Sulphides, Arsenides, Tellurides, etc., 

 — II, Oxides, — III, Silicates, and — IV, Sundries, the minerals 

 are arranged in the order in which they are given in Dana's 

 System of Mineralogy. 



AVe desire to expi'ess our thanks to Prof. Thomas Egleston, 

 of the School of Mines, Columbia College, who has again placed 

 us under obligations by supplying many of the rarer minerals. 



