Potassium permanganate in Iron Analysis. 291 



purest form of iron known, it would seem that potassium per- 

 manganate titrated against this might be expected to give trust- 

 worthy results for the first comparison. 



For the production of a definite amount of electrolytic iron 

 two different courses are open to us. Either a weighed amount 

 of a pure iron salt, as ammonio-ferrous sulphate, may be taken 

 and the iron completely precipitated by electrolysis ; or an 

 indefinite quantity of the salt may be taken and subjected to 

 electrolysis for a time, and the amount of iron determined by 

 weighing the electrolytic deposit. After some preliminary 

 trials, this second method has recommended itself to me as 

 being much more rapid than the first-mentioned method and 

 also free from some manipulatory details which render the first 

 difficult to be done with exceeding accuracy. 



Some experiments were therefore undertaken to compare 

 the amount of iron determined by direct weighing of the elec- 

 trolytic deposit with the amount determined by titration of the 

 solution of this same iron with potassium permanganate. The 

 details of the experiments were as follows. The solution of 

 potassium permanganate was first accurately standardized with 

 ammonium oxalate which had been shown to give identical 

 results with those obtained by the use of lead oxalate. About 

 10 grams of ammonio-ferrous sulphate were dissolved in about 

 150 cubic centimeters of water, 5 cubic centimeters of a satu- 

 rated solution of potassium oxalate were added, and then the 

 whole was heated with a considerable quantity of solid am- 

 monium oxalate until a clear solution was obtained. This solu- 

 tion was decomposed in a beaker between two platinum elec- 

 trodes, the iron being deposited on a piece of platinum foil of 

 a size convenient to be inserted in a rather large weighing 

 bottle, in which it was weighed both before and after the elec- 

 trolysis. From \\ to 1^ hours, with a current of 2 amperes, 

 was in general found to be sufficient to precipitate from "4 to 

 •5 grams of pure iron, and it was found unadvisable to use 

 a current much stronger than 2 amperes, since a higher current 

 showed a tendency to render the deposit less smooth and com- 

 pact. After washing, drying and weighing in the usual way, 

 the iron was dissolved in hydrochloric acid, the weighing bot- 

 tle being used instead of the small flask ordinarily employed 

 in this operation, the oxidized iron was reduced w r ith zinc, and 

 finally titrated with the potassium permanganate solution in 

 presence of sulphuric acid and a large amount of water. 



The following table shows the results obtained, the first 

 column giving the weight of the electrolytic deposit of iron, 

 and the second the weight of iron found in the solution of the 

 preceding upon titration with potassium permanganate previ- 

 ously standardized on ammonium oxalate. 



An. Jour. Sci. — Third Series, Vol. XLYIII, No. 286. — October, 1S94. 

 19 



