50 Brown — Work on the Interaction of Hydrochloric Acid. 



Here it is seen that, as shown by Wagner, less permanganate 

 is required to bring about final coloration in those experiments 

 in which manganous sulphate or chloride was used than in 

 their absence. From the experiments recorded in Table IV, 

 it must be concluded that this diminishing effect is due to the 

 intervention of the Guyard reaction so that the higher oxides 

 of manganese are formed in larger proportion by the introduc- 

 tion of the manganous salt, thus giving more material (if we 

 disregard the volatile and indefinitely reacting chlorine when 

 it is retained in solution) to oxidize the oxalic acid. Wagner 

 has attributed this diminishing effect to a slowing of the reac- 

 tion between hydrochloric acid and thinks such is the protect- 

 ing influence of a manganous salt in titrations of ferrous salts 

 by potassium permanganate in the presence of hydrochloric 

 acid. It is a diminishing of the reaction between hydrochloric 

 acid and potassium permanganate, but this diminishing is dne 

 to the formation of higher oxides of manganese, which, as is 

 well known, are less easily reduced by hydrochloric acid than 

 is the permanganate itself. Such action is unquestionably the 

 intervention of the Guyard reaction, as first suggested by 

 Zim merm ann. * 



It has been found that with each of the salts which Wagner 

 regards as catalyzers the apparent catalytic effect is entirely or 

 largely due to the chlorine retained in solution. The question 

 therefore arises : In what way does the chlorine affect the 

 result? It is evidently effective in oxidizing the oxalic acid. 

 It seemed likely, therefore, that the lesser oxidation of the 

 oxalic acid, necessitating a greater amount of permanganate to 

 bring about final coloration, in the presence of the various 

 chlorides used, is due to a lesser retention of chlorine in the 

 presence of these salts. It was decided, therefore, to deter- 

 mine the chlorine retained in solution under the varying condi- 

 tions, and also the residual higher oxides of manganese or with 

 the chromic chloride the chromate formed during digestion, 

 thus obtaining the total oxidizing value of the material 

 retained in solution at the close of the hour's digestion. For 

 this purpose potassium permanganate was digested with hydro- 

 chloric acid in the presence and absence of the various salts 

 used in the preceding experiments of this paper for one hour 

 at a temperature of 50° C. as there indicated. The flask con- 

 taining the -liquids was sealed to a Voit flask, to which was 

 fitted in a ground joint a return condenser approximately 60 cm 

 in length and with a bore approximately 3 cm in diameter. At 

 the close of the hour's digestion this condenser was removed, 

 * Ann. Ckem., ccxiii, 311 (1882). 



