Organic Acids in the Examination of Minerals. 23 



anhydride disengaged being accompanied by a gas having an 

 excessively irritating odor and exciting tears. This peculiar 

 substance is probably the same as that obtained in 1847 by 

 Plantamour,* by the action of chlorine on sodium citrate, and 

 which was subsequently studied by Laurent, by Staedler, and 

 by Cloez.t The latter showed the irritating body to be per- 

 chlorinated acetate of methyl, C 3 C1 6 2 , and explains its 

 formation as follows :| 



H 3 C 6 H 6 O 7 +H 2 O+16Cl=C 3 Cl 6 O. 2 4-3CO. 2 +10HCl. 

 Precisely how the action proceeds with potassium chlorate 

 and citric acid we have not determined; it is undoubtedly 

 more complex than even the following equation indicates : — 



26KClO 3 +27H 3 C 6 H 5 O 7 =30 3 ClA+45GO 2 +45H 2 O+8KCl4- 

 18KH 2 C 6 H 6 7 . 

 Tartaric acid behaves exactly like citric acid with the ni- 

 trate and the chlorate. Oxalic acid decomposes them in very 

 concentrated solutions and attacks the nitrite very actively , 

 probably in the following manner : 



2KN0 2 4-3H 2 CA=2KHC 2 4 +2H 2 0+2C0 2 +^A. 



Acetic and formic acids do not decompose the nitrate nor 

 the nitrite. 



19. These interesting reactions enable us to attack many 

 mineral sulphides with the greatest ease. With potassium 

 nitrite and citric acid, they are decomposed in the cold; 

 with the nitrate and chlorate, only on boiling. Pyrites, for 

 example, in fine powder, is very quickly decomposed by these 

 powerful agents, and completely dissolved, save a little sul- 

 phur. The solution contains ferric sulphate and hydropotas- 

 sium citrate, while both nitric oxide and carbonic anhydride 

 are evolved abundantly ; the reaction then may be formulated 

 as follows : — 



4FeS 2 +26KN0 3 +12H 3 C 6 HA = 2Fe 2 (S0 4 ) 3 +2K 2 S0 4 + 

 11K 2 H. C 6 H A + 15H 2 + 13N A + 60O 3 . 



* Berzelius, Jahresbericht, Vol. xxvi, p. 428. 



t Annals de Chimieet de Physique, (3) xvii, 297 and 311. 



| Cf. Watts' Dictionary, I, 996. 



