264 Gooch and Austin — Oxidation of Manganese. 



known permanganate and the sulphate, upon the assumption 

 that two molecules of the former throw down five molecules 

 of the hydrated dioxide, should disclose the error of the analy- 

 tical process when applied to the estimation of manganese 

 dioxide. In all probability the assumption that it is the 

 dioxide that is precipitated, and which afterwards acts upon 

 the iodide, is not quite true under the conditions, since the 

 precipitation takes place in presence of an excess of a manga- 

 nous salt ; but for our purpose it does not matter, since we 

 are in effect simply dealing with the oxidizing power of a 

 known amount of permanganate. 





Table II. 





Mn theoretically 

 precipitated by 

 KMn0 4 as Mn0 2 . 



Mn in Mn0 2 

 corresponding 

 to iodine found. 



Error of the analytical 

 process (applied to Mn0 2 ) 

 in terms of Mn. 



grm. 



grm. 



grm. 



0-1351 



0-1347 



0-0004 — 



0-1351 



0-1347 



0-0004 — 



0-1351 



0-1350 



o-oooi — 



0-1351 



0-1353 



0-0002 + 



01351 



0-1358 



0-0007 + 



0-1351 



0-1353 



0-0002 + 



Thus, it is obvious that the mean error of the results is prac- 

 tically inconsiderable, varying between extremes of —0-0004 

 grm. and +0*0007 on 0*1351 grm. of manganese dioxide. 



In the experiments of Table III the precipitated oxide was 

 treated with an excess of a standard arsenious acid solution and 

 5 cm3 of sulphuric acid of half strength, and the whole was 

 heated until the manganese dioxide was dissolved. To this 

 liquid was added tartaric acid (10 grm.) to prevent the precipi- 

 tation of the manganese and the oxidation by iodine in the 

 subsequent titration, the acid was neutralized by acid potassium 

 carbonate, and the arsenic still remaining in the arsenious con- 

 dition titrated by standard iodine. 





Table III. 





Mn precipitated 

 by action of KMn0 4 

 on MnS0 4 as Mn0 2 . 



Mn in MnQ 2 

 corresponding to 

 As 2 3 oxidized. 



Error of the process 

 in terms of Mn. 



grm. 



grm. 



grm. 



0*1392 



0-1396 



0*0004 — 



0-1109 



0-1117 



0*0008 — 



0-1112 



0-1117 



0-0005 — 



0-1109 



0-1117 



0*0008 — 



0-1109 



0-1117 



0*0008 — 



0-1117 



0-1125 



0-0008 — 



