H. D. Newton — Iron hy Potassium Permanganate. 343 



Art. XXXIX. — The Estimation of Iron hy Potassium Per- 

 manganate after Reduction with Titanous Sulphate; by 

 H. D. Newton. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — clxxiii.] 



Knecht* was the first to point out and recommend the 

 use of titanium sesquioxide and its salts in volumetric opera- 

 tions where a rapid and powerful reducing agent is required. 

 Somewhat later the same author in collaboration with E. Hib- 

 bertf published a method for the direct titration of ferric 

 chloride by a standard solution of titanous chloride, using 

 potassium sulphocyanate as an indicator, the reaction between 

 the two salts taking place according to the following equation : 



FeCl 3 + TiCl 3 = FeCl 2 + TiCl 4 . 



According to these authors, the above method yields excel- 

 lent results, and rapidly. The only precautions necessary are 

 that the solution of titanous chloride, being naturally very 

 sensitive to the action of atmospheric oxygen, must, after 

 being boiled in presence of marble to expel occluded oxygen, 

 be kept under a constant pressure of hydrogen. It has been 

 found, however, that even with such precautions the standard 

 of the solution gradually changes, and must be checked from 

 time to time against known amounts of ferric iron. 



The present investigation was undertaken for the purpose of 

 adapting the well known and accurate method of titration 

 with standard potassium permanganate to the determination 

 of ferrous salts, after reduction has been effected by a tita- 

 nous salt according to the excellent and rapid method of 

 Knecht. 



It has been shown in a former papery that bismuth oxide 

 completely oxidizes titanous sulphate while having no appre- 

 ciative effect on salts of ferrous iron. So the plan of this work 

 has been to reduce the iron by titanous sulphate, oxidize the 

 excess of titanous sulphate by bismuth oxide, and titrate the 

 remaining ferrous salt by permanganate. 



A solution of titanous sulphate of convenient strength was 

 made up by mixing twenty grams of commercial titanic acid, 

 in two portions, with three times its own weight of a mixture 

 of sodium and potassium carbonates and fusing in a platinum 

 crucible until all the titanic acid was converted into the soluble 

 alkali titanates. The melt obtained in this manner, after being 

 finely ground, placed in a platinum dish and treated with hot 

 concentrated sulphuric acid (which soon effected solution) was 



*Ber. Dtsch. Gesellsch., xxxvi. 166-169. flbid., xi, 3819. 



\ This Journal, vol. xxiii, p. 365. 



