Gooch and Peters — Titration of Oxalic Acid. 461 



Akt. LI. — The Titration of Oxalic Acid by Potassium 

 Pertnanganate in presence of Hydrochloric Acid; by F. A. 

 Gooch and C. A. Peters. 



[Contributions from the Kent Chemical Laboratory of Yale University — LXXXIL] 



Lowenthal and Lenssen* were the first to show that the 

 titration of a ferrous salt by potassium permanganate in the 

 presence of hydrochloric acid, according to the process of 

 Marguerittef is vitiated by the evolution of chlorine outside 

 the main reaction, and to point out that a remedy for the diffi- 

 culty is to be found in the titration of the ferrous salt in 

 divided portions, other equal volumes of the ferrous solution 

 being added to the liquid in which the first titration is accom- 

 plished until the amount of iron indicated by successive titra- 

 tions becomes constant. 



KesslerJ showed the restraining influence of certain sul- 

 phates, of manganous sulphate in particular, upon the irregular 

 and undesirable interaction of the permanganate and hydro- 

 chloric acid, and Zimmermann,§ in apparent ignorance of 

 Kessler's forgotten proposal, advocated the introduction of a 

 manganous salt, best the sulphate, into the ferrous salt to be 

 determined, thus accomplishing the purpose of the empirical 

 procedure of Lowenthal and Lenssen. 



The tendency toward evolution of chlorine in the oxidation 

 of a ferrous salt by permanganate, as compared with the 

 absence of such tendency in the similar oxidation of oxalic 

 acid, in presence of hydrochloric acid, was explained .by Zim- 

 mermann on the hypothesis that an oxide of iron higher than 

 ferric oxide is formed as an intermediate product, and that 

 this unstable oxide is sufficiently active to break up hydro- 

 chloric acid as well as to oxidize more of the ferrous salt. 

 Quite recently, Wagner|| finds explanation of the sensitiveness 

 of the hydrochloric acid solution of the ferrous salt in the 

 probable formation of chlor-ferrous acid (analogous to chlor- 

 platinic and chlor-auric acids), which suffers oxidation more 

 readily than hydrochloric acid under the action of the perman- 

 ganate. The protective influence of the manganous salt turns 

 apparently, as Zimmermann suggested, upon the initiation of 

 Guyard's reaction, according to which the permanganate and 

 manganous salt interact to form a higher oxide of manganese 

 of a constitution approaching the dioxide more or less closely — 

 this oxide being capable of oxidizing the ferrous salt, but slow 



* Zeit. f. Anal. Chern., i, 329. f Ana. d. Chim. et d. Phys. [3], xviii, 244. 



X Ann. d Phys. u. Chem., cxviii, 48; cxix, 225-226. 

 ^ Ann. d. Chem., ccxiii, 302. 



|( Maasanalytische Studien, Habilitationsschrift, Leipzic, 1898. 



