368 IRON, NICKEL, COBALT, &c. 



the common colourless protomuriate of manga- 

 nese obtained. But the red sulphate of manga- 

 nese may be concentrated without losing its co- 

 lour. Sulphurous acid, or nitrous acid, instantly 

 renders it colourless, by depriving it of the ex- 

 cess of oxygen which it contains above the pro- 

 tosulphate. 



^ us> besides the protoxide of manganese, there 

 are two other oxides, both of which are black. 

 I determined the composition of the brownish 

 black oxide in the following way : A quantity of 

 carbonate of manganese, which I knew to con- 

 tain exactly 45 grains of protoxide, was dissol- 

 ved in nitric acid in a platinum crucible ; the 

 solution was evaporated to dryness, and the cru- 

 cible with its contents was then exposed to a red 

 heat : by this means, the nitric acid was decom- 

 posed, and driven off, and a black shining pow- 

 der obtained, which weighed exactly 50 grains. 

 This black powder possesses the same properties 

 with the brownish black powder obtained by ex- 

 posing native black oxide of manganese to a low 

 red heat for it forms the same red coloured 

 solutions with sulphuric and muriatic acids, 

 which are rendered colourless by sulphurous 

 acid, or when heated with sugar.* 



* When carbonate of manganese is exposed to a red heat, it assumes a 

 brown colour ; but is not converted into deutoxide, unless it be previously 

 mixed with nitric acid. A quantity of carbonate containing 4<-5 grains 

 of protoxide of manganese, when thus treated, instead of weighing 5 grains 

 as it would do if it were converted into deutoxide, only weighs 4-8 or 



