USEFUL METALS 265 



Missouri, and Cumberland, England, they are Carboniferous. 

 The \Vcstphalian ores lie often in the Devonian limestones, while 

 in the Alpine district, in Carinthia, the zinciferous ores are most 

 abundant in the Triassic limestones. 



Methods of Extraction. (1) The Calcination Process. The 

 sulphide ore is first calcined to liberate the sulphur and convert 

 the metal into its oxide according to the following equation: 

 ZnS+3O = ZnO+SO 2 . If the ore is the carbonate it is also cal- 

 cined to drive off the carbonic acid present according to the equa- 

 tion, ZnCO 3 = ZnO+C02. If the ore is the oxide it may also 

 be calcined to drive off any sulphur that may be present or liber- 

 ate any other volatile constitutents. The oxide obtained by 

 calcination is dissolved in dilute mineral acid, precipitated as a 



tNO.JniN.Jo. 



FIG. 132. Zinc mine and mill of the Northern Ore Company, Edwards, 



New York. 



carbonate, and converted into its oxide, which is finally reduced to 

 the elemental state with charcoal obtained from sugar (Fig. 132). 



(2) The Electrolytic Process. According to Ashcroft and Swin- 

 burne, good results are obtained by this process and a large inter- 

 est is attached to the method which is especially applicable to the 

 sulphides of zinc. 



(3) Fusing with Calcium Carbide. In some localities the 

 sulphides of zinc are fused with calcium carbide and from the 

 resulting product several useful metals, as copper, etc., are easily 

 obtained. 



(4) Distillation. At lola, Kansas, a considerable amount of 

 zinciferous ores have been treated with natural gas as a fuel. 

 The standard furnace distills 25,000 Ib. of ore with 45 per cent, of 



