266 Gooch and Austin — Oxidation of Manganese. 



The results show plainly that, while the manganese is so com- 

 pletely precipitated in the chlorate process of oxidation when 

 properly conducted that only insignificant traces may escape, 

 the condition of oxidation cannot be taken to be that of the 

 dioxide. The average error thus put upon the determination 

 of the manganese known to be present is more than two per 

 cent. It follows, as a matter of course, that the indications of 

 any process which rests upon the assumption that the oxygen 

 value of the manganese compound precipitated in the chlorate 

 process corresponds to that of the dioxide must of necessity be 

 erroneous. If, therefore, the chlorate method is to be em- 

 ployed for the separation of the manganese, it is obvious that 

 precautions must be taken to secure a definite condition of 

 oxidation of the manganese before processes which depend 

 upon the oxygen value of the higher oxide may be applied for 

 the estimation of that element. The process which in our 

 hands seems to give the oxide in definite condition is based 

 upon the observations of Wright and Menke* that a dilute 

 solution of potassium permanganate acting in excess, at 80° C, 

 in the presence of zinc sulphate, and in thorough mixture upon 

 manganous sulphate, yields an oxide which, though com- 

 bined with alkali, holds the oxygen exactly in the propor- 

 tion corresponding to the dioxide. Three-fifths of the man- 

 ganese in such a precipitate represents the amount of that 

 element originally present in the manganous salt. In the fol- 

 lowing table are given the results of experiments in which 

 manganese was determined iodometrically after the interpola- 

 tion of the permanganate treatment. 



In these experiments a solution of manganous chloride of 

 known strength was drawn from a burette, evaporated to dry- 

 ness in a small beaker, heated with nitric acid until there was 

 no evidence of the presence of nitrogen oxides. Strong nitric 

 acid was poured in until the volume was 85 cm3 , sodium chlorate 

 (5 grm.) was added carefully, the liquid was boiled five min- 

 utes, more nitric acid (15 cm3 ) and a few crystals of the chlorate 

 were introduced, and the solution brought to boiling tempera- 

 ture again. After cooling, the liquid was filtered on asbestos 

 and washed with water, and the oxide upon the asbestos and 

 walls of the beaker was dissolved in 2 cm3 of hydrochloric acid. 

 After diluting a little the solution was evaporated with 5 cm3 of 

 strong sulphuric acid until no more hydrochloric acid remained. 

 The solution of manganous sulphate (not exceeding 0.5 grm. of 

 the salt), very nearly neutralized by potassium carbonate, was 

 mixed with a solution of zinc sulphate (2 grm.) and a freshly 

 and carefully filtered dilute solution of potassium permanga- 

 nate (1*5 grm. of the salt), the liquid, amounting now to about 



* Jour. Chem. Soc, xxxvii, 36. 



