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5S Dr, Forchhammer on pure Sahs of Manganese, [Jan* 



contain a small quantity of deutoxide which occasions their red- 

 dish colour, and the carbonate being obtained from them of 

 course contains the same. That the red colour of the solutions 

 of manganese depends upon the presence of deutoxide, I had 

 ^ opportunity of observing in the following way : 



In my paper on the Acids of Manganese, I have mentioned 

 the mode in which I decomposed the brown compound of lead, 

 manganese, and oxygen, by bisulphate of potash ; and I made 

 use of the same method for ascertaining the quantity of oxygen 

 combined with protoxide in the deutoxide and peroxide. I 

 fpund that when the greater part of the oxygen was expelled by 

 the combined action of heat and the bisulphate of potash, the 

 powder was entirely dissolved, and formed a beautiful transparent 

 amethystine coloured solution, which still yielded oxygen, and 

 became of a pink colour. The expulsion of oxygen did not 

 cease until the melted salt in the retort was entirely colourless, 

 and it remained so when cold. A solution of it in water was 

 colourless, but, when exposed to the air, it soon acquired the 

 slight pink colour, which is characteristic of all the salts of man- 

 ganese. This experiment proves obviously that the colour 

 depends upon the surplus of oxygen combined with the protoxide, 

 or that all these pink-coloured, solutions and salts contain both 

 protoxide and deutoxide ; the latter, however, only in very small 

 quantity. 



The way I proceeded in order to obtain pure protoxide was 

 this : 1 filled a glass tube, open at both ends, with deutoxide, 

 and heated it over a lamp while I passed hydrogen gas through 

 it. The brown powder soon changed to a light yellow, which 

 colour, while the powder was cooling, became white, and 

 the cold oxide was of a beautiful light-green. This colour, 

 however, changed in the air ; for while I was taking the open 

 tube to a pair of scales in another room, it evidently attracted 

 oxygen, and its colour changed into greyish-green ; and when 

 converted by combustion again into deutoxide, it gained five 

 per cent. 



There is not any reason to induce us to suppose that in this 

 case the protoxide had been reduced to suboxide by the action 

 of hydrogen, for the heat was very gentle, and from the power 

 with which the metal decomposes water even in the common 

 temperature of the atmosphere, we scarcely can expect that in 

 so slight a heat, hydrogen should deprive the protoxide of a part 

 of its oxygen. 



To ascertain the quantity of oxygen in the protoxide, I ana- 

 lyzed the sulphate and carbonate. 



I heated a certain quantity of sulphate of manganese to red- 

 i^e^s, then dissolved it, and precipitated the sulphuric acid by 

 nitrate of barytes. Five grammes of perfectly dry sulphate of 

 manganese gave me 7*913 grammes of sulphate of barytes^ 



