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PYROLUSITE. 
Pyrolusite is a dark grey to iron black mineral composed 
of manganese dioxide (Mn0 2 ). It is also known as black oxide 
of manganese, or, less properly, as black oxide. Owing to the 
property it possesses of neutralizing the colour in glass due to 
silicate of iron, it is sometimes called glass makers' soap. 
USES. 
When manganese dioxide and potassium chlorate are mixed 
together and heated, oxygen is given off. This is one method 
adopted for producing oxygen for industrial purposes, but it 
is being superseded by the electrolytic and liquid air methods. 
Pyrolusite is used in the manufacturing of electric dry 
batteries. It should analyse at least 85 per cent manganese 
dioxide and not over one-half of one per cent ferric oxide. 
In the melting of bronzes, manganese dioxide is added to 
the crucible as a desulphurizer. 
As referred to before, pyrolusite is used for counteracting 
the green colour of glass due to silicate of iron, introduced by 
impurities. Manganese dioxide when added to the glass mix 
ture gives a purplish tint, this colour is complementary to the 
green and thus destroys it, producing a colourless glass. It 
is used for the same purpose in porcelain manufacturing and 
enamelling on sheet metal. For these purposes the mineral 
should be as free from iron as possible. 
Pyrolusite is used extensively in the manufacturing of 
varnish. It acts as a drier. For this use it should be high 
grade, very finely ground, and free from siliceous impurities. 
Prices range, according to purity and quantity purchased, 
from $17 to $80. The average price paid by glass manufacturers 
is $21 per ton.