REPORT ON CHEMISTRY. 
477 
acid compounds of this metal have lately been studied by 
Mitscherlich with equal success. 
When peroxide of manganese is fused in the open air with 
an equal weight of caustic potash, and the mass afterwards 
treated with water, a green solution is obtained, which must be 
decanted, not filtered, through paper. This solution, evapo¬ 
rated in the receiver of an air-pump, gives green crystals of 
manganate of potash. These crystals are isomorphous with 
the sulphate and chromate of potash, and the acid they con¬ 
tain is composed of 1 atom manganese + 3 atoms oxygen 
= M-f 3 O. 
These crystals may be redissolved in caustic potash and 
crystallized without decomposition; but if the solution be ex¬ 
posed to the air till the alkali attracts carbonic acid, a brown 
powder, which is a compound or mixture of the hydrates of 
the pro- and jp^r-oxides, is precipitated, and the solution be¬ 
comes red. Evaporated on a sand-bath red crystals are ob¬ 
tained, which are permanganate , and are isomorphous with 
the perchlorate of potash. The acid they contain consists of 
two atoms manganese and seven atoms oxygen = 2 M + 7 O. 
This salt in solution rapidly decomposes when heated, and 
slowly when set aside in a diluted state, and becomes finally 
green, passing through the series of changes from that colour 
to red, to which it owes its name of chameleon mineral *. 
The known compounds of oxygen and manganese are as 
follow:— 
Protoxide . . = M + O 
Sesquioxide — 2 M + 3 O 
Peroxide . . . = M + 2 O 
Red oxide . . = 3 M + 4 O 
Varvicite. 
Manganic acid . . 
Permanganic acid. 
4 M+7 O 
M + 3 O 
2 M + 7 O 
Zinc. —De la Rive f has made an interesting observation re¬ 
garding the action of sulphuric acid on metallic zinc. He 
found that distilled zinc is much more slowly dissolved in dilute 
acid than the zinc of commerce. This he attributes to the elec¬ 
trical agency of the foreign metals, especially iron, which it 
contains; and this explanation is confirmed by the fact that 
when a thick platinum rod was fastened to a piece of zinc it 
evolved twice as much hydrogen in a given time as when placed 
in the acid alone. An acid containing from fifty to seventy 
per cent, of water dissolves the zinc most rapidly. 
Oxide of zinc. —By heating metallic zinc in an atmosphere 
* Ann. de Chimie, xlix. p. 113. 
f Ibid, xliii. p. 425. 
