1. The _protoxide_ may be obtained from a solution of the sulphate by
precipitation with carbonate of potash, and expelling the carbonic acid
from the washed and dried carbonate, by calcination in a close vessel
filled with hydrogen gas, taking care that no air have access during the
cooling. It is a pale green powder, which slowly attracts oxygen from
the air, and becomes brown; on which account it should be kept in glass
tubes, containing hydrogen, and hermetically sealed. It consists of
77·57 metal and 22·43 oxygen. It forms with 24 per cent. of water a
white hydrate; and with acids, saline compounds; which are white, pink,
or amethyst coloured. They have a bitter, acerb taste, and afford with
hydrogenated sulphuret of ammonia, a flesh-red precipitate, but with
caustic alkalis, one which soon turns brown-red, and eventually black.
2. The _deutoxide of manganese_ exists native in the mineral called
_Braunite_; but it may be procured either by calcining, at a red heat,
the proto-nitrate, or by spontaneous oxidizement of the protoxide in the
air. It is black; when finely pulverized, dark brown, and is
convertible, on being heated in acids, into protoxide, with
disengagement of oxygen gas. It consists of 69·75 metal, and 30·25
oxygen. It forms with 10 per cent. of water, a liver-brown hydrate,
which occurs native under the name of _Manganite_. It dissolves readily
in tartaric and citric acids, but in few others. This oxide constitutes
a bronze ground in calico-printing.
3. _Peroxide of manganese_; _Braunstein_, occurs abundantly in nature.
It gives out oxygen freely when heated, and becomes an oxidulated
deutoxide. It consists of 63·36 metal, and 36·64 oxygen.
4. _Manganesic acid_, forms green-coloured salts, but has not hitherto
been insulated from the bases. It consists of 53·55 metal, and 46·45
oxygen.