Gooch and Austin — Oxidation of Manganese. 261 



the sodium chlorate, and discontinuing the heating as soon as 

 the liquid again boils, the insolubility of the manganese is so 

 great that no more than insignificant traces may be recovered 

 from the filtrate after cooling, filtering upon asbestos and wash- 

 ing with water. The test for manganese in the filtrate and 

 washings was made after evaporation and solution of the resi- 

 due in distilled water by treating the hot solution with bromine 

 and ammonia. In the first division of the table below are 

 results obtained by treating the manganese precipitated from 

 the filtrate with potassium iodide and sulphuric acid, the iodine 

 set free being determined by sodium thiosulphate. In the 

 second series the precipitated manganese dioxide was reduced 

 by a known amount of decinormal arsenious acid and the 

 amount remaining unoxidized was estimated by titration with 

 iodine in the presence of acid potassium carbonate. 





Table I. 







Mn found by KI 



Mn found by 



Mns04 



treatment in 



As 2 3 treat- 



taken. 



filtrate. 



ment in filtrate 



grm. 



grm. 



grm. 



0'33()1 



none 



. 



0-3361 



none 



. . _ - 



0*3361 



0-00006 



- _ _ - 



0'3361 



0-00005 



_ 



03361 



0*00002 





0-3361 



0-00008 



_ _ - - 



0-3361 



none 







0*4128 





0-00003 



0-4128 







0-00003 



0-4128 







Trace 



0*4128 







Trace 



It will be seen that in no case did the manganese which 

 escaped precipitation — that which corresponded to the iodine 

 freed or the arsenious acid oxidized — exceed 0*0001 grm. 

 Plainly this modified method of handling the chlorate process 

 may be trusted to precipitate the manganese with gratifying 

 rapidity and approximation to completeness. Our experience 

 has shown plainly that prolonged boiling results in a considera- 

 ble loss of manganese (from 0*0010— 0*0030 grm.). This we 

 think is due to the solvent effect of the lower oxides of nitro- 

 gen naturally produced (as is always the case in boiling nitric 

 acid) after the chlorine dioxide has been thoroughly expelled. 

 An excess of the chlorate at the end of the boiling seems to be 

 essential and a slight yellow color in the solution, due to chlo- 

 rine dioxide, is a favorable indication rather than the reverse. 

 We find it best to filter the undiluted nitric acid, under pressure, 



