Organic Acids in tlic Exaniinatioii uf Minerals. \) 



28. The minenils of tlie foregoing list were submitted to tlie 

 action of the following retigents successively : (1) A solution of 

 citric acid saturated at the temperature of the laboratory, say 

 65° to 70° Fahrenheit; ihis Ave call simjily "citric acid."' 

 (2) The same solntion to which solid sodium (or potassium) 

 nitrate is added, which for couvenience we shall call the "nitro- 

 citric mixture " (8) The same solution to which solid potas- 

 sium iodide is added at the time of testing, and which for sim- 

 plicity we shall designate as the "iodo-citric mixture." 



The action of these reagents was studied in the simple manner 

 detailed in our first paper. The mineral to be examined was 

 carefully freed from its associated gangue and finely pul- 

 verized in an agate mortar ; a portion was placed in a test-tube, 

 the solution of the acid was added, and the resulting phenomena, 

 in the cold, and on boiling, carefully noted. In man}^ instances 

 the partial decomposition of the mineral was ascertained by filter- 

 ing from the residue, and testing the solution with an appro- 

 priate rccigent ; or by examining the disengaged gas with a suit- 

 able test-paper. 



Sulphides, Arsenides, etc. 



29. Minerals of this group treated with citric acid alone, 

 yielded results as follows : 



(«) Clausthalite and leucopyrite dissolve in the cold with- 

 out liberation of gas. 



(h) Alabandite is very strongly attacked in the cold, with 

 evolution of sulphuretted hydrogen. On applying heat 

 it is wholly soluble. In this respect alabandite appears 

 to be the most easily decomposed of all the sulphides 

 yet examined, 37 in number. 



(c) Boulangerite, Jamesonite, and kermesite are more or 

 less attacked by boiling citric acid, yielding sulphuret- 

 ted hydrogen. The remaining minerals of this group 

 resist the action of cold or hot citric acid. Sulphur is 

 absolutely unattacked even when the citric acid solu- 

 tion is heated to the melting point of the element. 

 The powerful solvent action of a mixture of citric acid and 

 sodium nitrate was discussed in our first paper (19), here we 



