Gooch and Peters — Titration of Oxalic Acid. 463 



of a brownish-red precipitate rather than the clear pink of the 

 soluble permanganate, and it is obvious that in case the solu- 

 tions to be oxidized were not active enough to act with rapidity 

 upon the product of the Guyard reaction, difficulty might fol- 

 low the failure to adjust the conditions more particularly. 



It has been stated by Fleischer* and Zimmermannf that 

 hydrochloric acid interferes in no way with the titration of 

 oxalic acid by potassium permanganate. This statement, how- 

 ever, is not in accord with our experience ; for we find that in 

 such titrations there is a small though real waste of permanga- 

 nate proportionate to the amount of hydrochloric acid present. 

 This, fact is brought out clearly in the comparison of experi- 

 ments of section A in the following table, in which no hydro- 

 chloric acid was present, with experiments B, in which 

 hydrochloric acid was present. 





Temperature at 



beginning about 80° C. 





Approximate 

 volume at 

 beginning 



of titration. 



H 2 S0 4 

 1: 1 

 cm 3 . 



Ammonium 

 HCl oxalate 

 Sp.gr. 1-09. T \N. 

 cm 3 . cm 3 . 



A 



KMnO-4. 

 cm 3 



Variation from 



mean of A taken 



as standard. 



cm 3 . 



200 



5 





50 



47*50 



o-oo 



200 



5 







50 



47*50 



o-oo 



200 



10 





50 



47-50 



o-oo 



200 



10 



_ _ . _ 



50 



47-50 



o-oo 



200 



25 







50 



47-50 



o-oo 



200 



25 



— -- 



50 

 B 



25 



47*50 



o-oo 



f 150 



10 



2-5 



23-80 



+ 0-05 



j 150 

 j 150 



10 



2*5 



25 



23-90 



+ 0*15 



10 



5-0 



25 



23-90 



+ 0-15 



[ 150 



10 



10-0 



25 



24-00 



+ 0-25 



( 500 



5 







25 



23-80 



+ 0-05 



\ 500 



10 



10*0 



25 



24-00 



+ 0-25 



( 500 



10 



10-0 



25 



24-10 



+ 0-35 



From these results it is evident that, though the 

 duced by the presence of the hydrochloric acid 

 action of the permanganate upon the oxalic acid 



j error intro- 



during the 



is small, it is 



plainly appreciable. The questions arise, therefore, first, as to 

 whether the secondary action of the permanganate upon the 

 hydrochloric acid may be prevented by the presence of a suit- 

 able amount of a manganous salt, and, secondly, as to whether 

 in this event the reducing agent, — the oxalic acid — is suffi- 

 ciently active, like the ferrous salt, to prevent the premature 

 establishment of an end color due to the Guyard reaction. The 

 latter question must naturally be settled before the former can 



* Volumetric Analysis; Trans, by Muir, p. 71. f Loc. cit. 



