Zinc is a bluish white metal which has only lately been discovered in its pure form, though its ores have long been known and used. It is obtained from the ores in the following manner:

Zinc carbonate is reduced to zinc oxide by heating, thus:

ZnCO3

=

ZnO

+

CO2

Zinc Carbonate

Zinc Oxide

Carbon Dioxide

The sulphide may be oxidized to an oxide by wasting, thus:

ZnS

+

3O

=

ZnO

+

SO2

Zinc Sulphide

Oxygen

Zinc Oxide

Sulphur Dioxide

The oxide is finely powdered, mixed with charcoal, and heated in earthenware retorts. The heating process is continued until the temperature rises above the boiling point of zinc (918° C). The oxide then passes off as a gas and condenses in an iron receiver. Pure zinc may be obtained by repeated distillations in vacuum. The largest proportion of zinc comes into the market in ingots formed by pouring it into molds. In this form it is hard, crystalline in structure, and rather brittle, but at a moderately high temperature (212° to 300° F.) it possesses great malleability and ductility. It can then be readily drawn into wire, rolled into plates, or worked in other ways. Zinc is well suited for casting models, as it melts readily, liquefies completely, and therefore copies every line of the mold more accurately than do the harder metals. Zinc dust is obtained by distilling zinc and allowing it to condense in a cold chamber. Granulated zinc is made by pouring melted zinc into water.