308 RED COLOUR OF THE PROTOSALTS OF MANGANESE. 
on cooling solidifies to a tissue of colourless crystals. It 
being known that salts of manganese are very readily more 
highly oxidized in the presence of a superoxide and free 
dilute acid, as for instance peroxide of lead and dilute 
nitric acid, I assured myself that the red solution ob- 
tained by dissolving protocarbonate of manganese in dilute 
sulphuric acid, owes its red colour to an admixture of a 
higher oxide of manganese, for it is instantly decolorized by 
a few drops of sulphurous acid or an organic substance. It 
appeared to me beyond all doubt that the red colour was to 
be ascribed to a higher oxide, and that protoxide of manga- 
nese, perfectly free from oxide, yielded colourless salts; but 
in preparing a larger quantity of the colourless salt, by dis- 
solving pure protocarbonate of manganese, I obtained 
crystals which singly appeared colourless, but in mass ex- 
hibited a decided, though faint reddish tint. This slight 
colour could not be removed either by sulphurous acid, or- 
ganic substances or sulphuretted hydrogen ; it could there- 
fore not be ascribed to the presence of a higher oxide. The 
protocarbonate of manganese had been prepared with care, 
and tested as to its purity previous to solution in sulphuric 
acid; the slight reddish tint could therefore not be owing to 
any foreign substance. I am inclined to regard this faint 
colouring which the protosalts of manganese exhibit, and 
which cannot be removed by sulphurous acid, sulphuretted 
hydrogen, or any other reducing agent, as peculiar to the 
protosalts of manganese. 
The most usual cause however of the red colour of the 
protosalts of manganese, is owing to the presence of cobalt. 
In preparing the colourless salt, by treating commercial man- 
ganese with an excess of concentrated sulphuric acid, I ob- 
tained on dissolving the salt a solution, which even when 
largely diluted had a rose-red colour, which could not be 
made to disappear by sulphurous acid, or any other reducing 
agent. I was long in doubt respecting this red colour, but 
some experiments soon showed me that it arose from cobalt; 
and in fact nearly all the kinds of manganese which I have 
