(Zinc fused and poured into water).

Impurities. - Very frequently it contains sulphur or arsenic.

Tests. - Zinc is chiefly used for preparing hydrogen, and these impurities are tested by adding pure dilute hydrochloric or sulphuric acid to it and holding over it a piece of paper dipped in acetate of lead. If sulphur be present the paper is blackened. If the piece of paper be wetted with solution of nitrate of silver, a brown or black stain is produced if arsenic is present. On lighting the hydrogen and depressing a piece of porcelain on it, a black stain is produced if arsenic is present.