Zinc or Spelter, as it is often called in commerce, is a hard, bluish-white metal, lustrous on its surface. When broken, it exhibits a crystalline fracture. At ordinary temperatures it is somewhat brittle, but when heated above 212° F. it becomes so ductile and malleable, that it may be drawn into wire or rolled into thin plates. Since the discovery of this quality the uses of this metal, which formerly was employed chiefly in connection with copper in the manufacture of brass, have greatly extended. It is used for roofing, spouting, baths, water-tanks and for covering ships' bottoms instead of copper. As a material for casting artistic works zinc has the desirable properties of a low melting-point and of taking a sharp impression from the mold, so that it requires little labor from the chaser. It also possesses considerable hardness. It has, therefore, become a favorite material for making casts of statues and different kinds of ornaments. Another important use of metallic zinc is in the cells of electric batteries, in many of which the dissolving of the zinc is the source of energy. Zinc-oxide, a white powder, is extensively used as a pigment. Other compounds of zinc, as the chloride and the sulphate, are used in medicine.