22 Organic Acids in the Examination of Minerals. 



DECOMPOSITION OF MINERALS BY ORGANIC ACIDS AND 

 OXIDIZING AGENTS. 



18. Desirous of extending the use of organic acids in 

 attacking minerals, we tried the effect of adding oxidizing 

 agents to the solution of the acid ; the results were satisfac- 

 tory and prompted the following investigation : 



When potassium, sodium, or ammonium nitrate is added 

 to a boiling solution of citric acid, on reaching a certain degree 

 of concentration nitric acid is set free, and this immediately 

 reacts upon the organic acid, decomposing it with evolution 

 of gases. These gases proved on examination to consist of 

 nitric oxide and carbonic anhydride ; whether carbonic oxide 

 is present was not determined. The reaction which takes 

 place is very complex ; it may possibly be expressed thus : — 



4H 3 C 6 H 5 7 +6KN0 3 =7H 3 0+3K 2 HC 6 H 5 7 +6C0 3 +3N 2 3 



or admitting the formation of oxalic acid,* we may write: — 



11H 3 6 H S 7 +16K¥0 3 =8K 2 HC 6 H 5 7 +3H 2 CA+17H 2 



+120O 3 +8K 2 O 2 



Potassium nitrite also decomposes citric acid in a some- 

 what similar manner, the action beginning in the cold and 

 continuing with violence and a rise of temperature. The 

 reaction may be expressed as follows : — 



9H 3 C 6 H 6 7 +16KN0 2 =:8K 2 H.C 6 H 6 7 +H 2 CA+3H 2 0+81s T A 



+4C0 2 . 



Or, abbreviating and disregarding the decomposition of the 

 organic acid, we may have 



H 3 0+3KNO 2 =K 3 C+H:N03+H 2 0+NA. 



The nitric acid being then in a nascent condition, is prepared 

 to effect oxidation in a most powerful manner. 



When chlorate of potassium is substituted for the nitrate 

 or nitrite, the decomposition begins on boiling down the solu- 

 tion to small bulk, and proceeds very vigorously, the carbonic 



* Watts' Dictionary, T, 99G. 



