Gooch and Austin — Oxidation of Manganese. 265 



It is clear that either of these methods of reduction, the 

 action of an acidified iodide or that of arsenious acid, is capable 

 of yielding fairly accurate indications when we have to deal 

 with a pure salt of manganese. When, however, the manga- 

 nese is associated with a considerable amount of iron, as is 

 frequently the case, it becomes a matter of necessity to sepa- 

 rate the manganese before attempting its estimation. For this 

 purpose the " chlorate process " is by far the simplest of those 

 generally used, and though it has been the subject of much 

 discussion, it is at present the method of separation most 

 widely used by the practical chemists, whether the final estima- 

 tion of the manganese is made gravimetrically, as in Ford's 

 process, or volumetrically, as in the methods of Yolhard, Wil- 

 liams, or Pattinson. 



Definite portions of the solution of pure manganous chloride 

 were drawn' from a burette into an Erlenmeyer flask of 300 cc 

 capacity, evaporated to dryness, precipitated by the " chlorate 

 process" with the modifications given in detail above. The 

 oxide, after careful washing, was returned with the asbestos to 

 the flask and treated by one or other of the methods to be 

 described. It was either treated with potassium iodide 

 (5 grms.) and sulphuric acid (10 cc ) of half strength, the iodine 

 set free being estimated by thiosulphate ; or, it was heated 

 with an excess of standard arsenious acid and 10 cc of sulphuric 

 acid of half strength, and after cooling, adding 5 grm. of the 

 Rochelle salt and neutralizing with acid potassium carbonate, 

 the arsenious acid remaining unoxidized was estimated with 

 standard iodine. In Table IV are given the results obtained 

 from this work. 





Table IV. 







Mn taken in 



Mn found upon 





Mn found in the filtrate 



the form of 



the hypothesis 





after 



evaporation and 



manganous 



that Mn0 2 is 





treatment with bromine 



chloride. 



precipitated. 



Error. 



and ammonia. 



grm. 



grm. 



grra. 





grm. 





By reduction xwi 



th potassium 



iodide. 





0*1225 



0-1183 



0-0042 — 





0-00006 



0-1225 



o-im 



0-0048 — 





Trace 



0*1225 



0-1180 



0-0045 — 





0-00008 



0-1225 



0-1169 



0-0056 — 





Trace 





By reduction ivith arsenious 



acid. 





0-1222 



0-1189 



0-0033 — 



Not determined. 



0-1222 



0-1191 



0-0031 — 



« 



« 



0-1222 



0-1199 



0-0023 — 



M 



« 



0-1222 



0-1200 



0-0022 — 



(i 



a 



0-1222 



0-1186 



0-0036 — 





none 



0-1222 



0-1187 



0*0035 — 





0-0001 



0-1222 



0-1189 



0-0033 — 





0-0002 



0-1222 



0-1194 



0-0028— 





Trace 



0-1222 



0-1205 



0-0017 — 





o-oooi 



