RED COLOUR OP THE PROTOSALTS OF MANGANESE. 307 
nese by carbonate of potash, dissolving the washed proto- 
carbonate in sulphuric acid, precipitating it again, and re- 
peating this operation until a colourless solution is obtained. 
On each solution in sulphuric acid a portion of the intermix- 
ed higher oxide is said to be converted into protoxide and 
oxygen, and finally to disappear entirely. Since the proto- 
carbonate,on washing in the air, is readily oxidized higher, 
it is evident that the frequent precipitation is more injurious 
than advantageous. I shall subsequently show that, by one 
solution of the protocarbonate of manganese in sulphuric 
acid, the so-called colourless salt is obtained, when a suffi- 
cient quantity of concentrated sulphuric acid has been em- 
ployed. 
According to Brandes, the colourless salt is obtained when 
the pulverized sulphate is boiled in spirit or aether, and then 
dissolved in water, or when its solution is boiled with some 
sugar. According to Brandenburg, the colourless salt is 
obtained on heating to redness manganese with English oil 
of vitriol, and the red salt with fuming oil of vitriol. Gmelin, 
on the contrary, always obtained a coloured salt by igniting 
manganese with fuming or monohydrated sulphuric acid, 
which, on being heated to redness and again dissolved, af- 
forded a red solution, which could not be decolourized by 
sulphurous acid or continued boiling with sugar, even on 
the addition of sulphuric acid. He thence concludes that 
the red colour of the protosalts of manganese cannot be as- 
cribed to the presence of a higher oxide. Berzelius enter- 
tained the same view, and supposes the difference of colour 
to depend on isomerism. 
I have repeated all the above experiments, but without 
succeeding in obtaining a perfectly colourless salt. When 
protocarbonate of manganese, which has been washed and 
exposed to the air, is heated with dilute sulphuric acid, a very 
red solution is ohtained, while a brown powder remains un- 
dissolved: when, on the other hand, concentrated sulphuric 
acid is employed, a colourless solution is obtained, which 
