14 Organic Acids in the Examination of Minerals. 



I, Minerals decom^)osed by boiling with citric acid and 



sodium nitrate. 

 K. Minerals decomposed by heating with citric acid and 



ammoninm flnoride. 

 L. Minerals which are not attacked by any of these 



methods. 



To this we added, in a subseqnent paper, a twelfth group., 

 A'iz. : — 



M. Minerals decomposed by heating with citric acid and 

 potassium iodide. 



In the Tables accompanying this paper we have combined, on 

 a similar plan, the results obtained in the present and previous 

 communications, thus giving a comprehensive view of the be- 

 havior of two hundred minerals with citric acid. The arrange- 

 ment differs somewhat from the foregoing ; we have re-adjusted 

 the silicates to accord with facts stated in (32), and we have 

 omitted the reaction with ammonium fluoride as of no import- 

 ance in determining species. 



To ascertain the exact position for each mineral has been no 

 trivial task ; and should errors be discovered, we crave indulg- 

 ence, and beg our friends to remember the French saying : 

 " Ceux qui ne se trom^Jent jamais sont ceux qui ne font ritn.'" 



Summary. 



35. The number of minerals examined, though considerable, 

 if we ]'egard the labor involved, is but small compared with those 

 which remain to be treated by these methods, and any attempt 

 at generalization must be correspondingly weak. 



It may, however, be admissible to study the Tables with a view 

 to determining whether there is any relation, peculiar to the 

 organic acid, between its solvent power and the chemical consti- 

 tution of the minerals. This question may be considered from 

 two standpoints, corresponding to two methods of classifying 

 minerals, viz., with reference to their acidic and to their basic 

 constituents. 



(«.) The first method of grouping the minerals is the same as 

 that of the list given (37) ; the question apj^lied to them may be 

 answered thus : — 



