Brown — Hydrochloric Acid, etc. 31 



Art. IV. — The Interaction of Hydrochloric Acid and 

 Potassium Permanganate in the Presence of Ferric Chlo- 

 ride ; by James Brown. 



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



Lowenthal* and Lenssen were the first to show that the 

 titration of ferrous salts by potassium permanganate in the 

 presence of hydrochloric acid as proposed by Marguerittef does 

 not admit of quantitative accuracy because of the evolution of 

 chlorine by the interaction of hydrochloric acid and potassium 

 permanganate, and to propose as a remedy for this source of 

 error the titration of successive equal portions of the ferrous 

 salt to be determined until the readings become constant. 



This tendency tow r ard evolution of chlorine in titrations of a 

 ferrous salt by potassium permanganate in the presence of 

 hydrochloric acid as compared with the alleged absence of such 

 tendency in similar titrations of oxalic acid, was explained by 

 ZimmermannJ on the supposition that the oxidation of the 

 iron proceeds so rapidly as to form oxides of iron higher than 

 the sesquioxide which then react to oxidize more iron and 

 liberate chlorine from hydrochloric acid. Quite recently 

 Wagner§ explains this phenomenon by the assumed formation 

 of chlor-ferrous acid (analogous to chlor-platinic and chlor- 

 auric acids), which is more easily oxidized by the permanganate 

 than is hydrochloric acid under similar conditions. Recent 

 work [ has shown that there is a slight though real waste of 

 permanganate in titrations of oxalic acid under the conditions 

 named, and that this loss is proportional to the amount of 

 hydrochloric acid present. It still appears, however, that this 

 loss is greater in titrations of ferrous salts than in those of 

 oxalic acid under the conditions named. 



Wagner's work in relation to the phenomenon mentioned 

 above has been reviewed very carefully, and it has been found 

 that, although as shown by him more permanganate is required 

 to bring about final coloration against equal quantities of oxalic 

 acid in experiments in which equal quantities of potassium per- 

 manganate are digested with a constant quantity of normal 

 hydrochloric acid and a measured volume of tenth normal ferric 

 chloride than when an equivalent quantity of tenth-normal 

 hydrochloric acid is substituted for the tenth-normal ferric 

 chloride, the differences vary within wide limits and disappear 

 entirely if the chlorine formed by the interaction of the potas- 



*Zeit. Anal. Chem., i, 329. fAnn. Chim. [3], xviii, 244. 



JAiin. Chem., ccxiii, 311. 



§ Maassanalytische Studien, Habilitationsschrif t, Leipzig, 1898. 



I Gooch and Peters : This Journal [4], vol. vii, 463. 



