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Other “decolourizers” are sulphurous acid, permanganates and manganates, all of which have received application in the sugar industry.

The men were recommended to use, as a wash for the mouth, manganate of potash.

This retains its colour after washing and drying, but cannot be recommended as a pigment, being liable to suffer in contact with organic substances, which deoxidize and decolourize the manganates and permanganates.

When carbon dioxide is passed through a solution of a manganate a part of the manganese is changed into manganese dioxide, while the remainder forms a salt of the unstable acid HMnO4, called permanganic acid.

The manganate of soda thus formed will color the fused mass of a bluish-green tint.