212 Gooch and Austin — Estimation of Manganese 



Mn0 2 , begins, as Wright and Menke have shown* to lose oxy- 

 gen at a temperature (about 210° C.) to which the hydrated 

 oxide must be heated to free it from water, or very nearly that 

 at which the nitrate is converted into the dioxide ; so that the 

 chance of producing an undecomposed dioxide by the ignition 

 of the hydrated dioxide (the form in which the dioxide gener- 

 ally appears in analytical processes), or of the nitrate, is small. 

 Manganic oxide, Mn 2 3 , is produced, it is said, from the other 

 oxides by ignition at a low red heat under the ordinary condi- 

 tions. The manganoso- manganic oxide, Mn 3 4 , forms, pre- 

 sumably, when an oxide of manganese is submitted, under 

 ordinary atmospheric conditions, to the high heat of the blast- 

 lamp. If the proportion of oxygen in the surrounding atmo- 

 sphere is reduced below the normal, the conversion of Mn 2 3 

 to Mn 3 4 goes on very easily, as Dittmar has shown,f at a tem- 

 perature between the melting points of silver and aluminum, 

 while if the proportion of oxygen in the surrounding atmo- 

 sphere falls much below the normal, the reverse change, from 

 Mn 3 4 to Mn 2 3 , tends to take place at the same temperature. 

 It is not surprising, in view of these phenomena, that the esti- 

 mation of manganese as the oxide Mn 3 4 should have fallen 

 into disrepute ; and yet, if the condition most favorable to the 

 production of that oxide — a low proportion of oxygen in the 

 surrounding air — can be maintained during the ignition, it is 

 not impossible that the indications of the process might prove 

 to be, under the conditions, reasonably accurate. Now, this 

 may be exactly the condition of affairs when the ignition takes 

 place ordinarily ; for, if the products of combustion displace 

 the ordinary air about the crucible, the proportion of oxygen 

 about the oxide falls to a low limit. We have made the 

 experiment of enclosing the ignited crucible within an inverted 

 crucible, so that the products of combustion should be held 

 immediately about and above the ignited oxide, but our experi- 

 ence has shown that the object in view is attained, apparently, 

 quite as well when the ignition is so arranged that the crucible 

 simply rests well within the upper part of the flame of a strong 

 Bunsen burner, or blast-lamp, in such manner that an oxidiz- 

 ing flame covers nearly the entire wall of the crucible. 



In the following experiments we have put to the test this 

 matter of getting definitely the different oxides of manganese. 

 We started with a known amount of pure anhydrous sulphate, 

 prepared from the pure chloride in the manner previously 

 described. This sulphate was converted by ignition into the 

 oxide — presumably the oxide Mn 3 4 — the containing crucible 

 being well within the upper flame of a powerful burner. 



*Jour. Chem. Soc, xxx, 775. f Jour. Chem. Soc, xvii, 294. 



