448 APPLIED SCIENCE 



520. Properties of Zinc. 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: 



ZnCO 3 = ZnO + C0 2 

 Zinc Carbonate Zinc Oxide Carbon Dioxide 



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



ZnS + 3O = ZnO + SO 2 

 Zinc Oxygen Zinc Sulphur 



Sulphide Oxide -Dioxide 



The oxide is finely powdered, mixed with charcoal, and 

 heated in earthenware retorts. The heating process is con- 

 tinued 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 struc- 

 ture, and rather brittle, but at a moderately high tempera- 

 ture (212 to 300 F.) it possesses great malleability and duc- 

 tility. 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. Granu- 

 lated zinc is made by pouring melted zinc into water. 



