266 ECONOMIC GEOLOGY 



coke or poor coal as a reducing agent. Unfortunately the supply 

 of natural gas at lola is becoming exhausted. 



Uses of Zinc. Zinc enters the marts of trade in the form of 

 rolled sheets, and also in cast cakes 1 in. in thickness. In 

 the latter form it is known as spelter. Spelter cakes are extremely 

 brittle and break with a crystalline fracture. If the metal is 

 pure, the crystal faces are large and present a smooth or perfect 

 cleavage. If small quantities of iron are present, dull spots 

 appear on the crystal face, and with only a small percentage of 

 iron present, the spelter breaks with granular fracture. Spelter is 

 seldom, if ever, pure. Particular notice should be given to iron 

 in spelter. The iron does not distill with the zinc. It comes from 

 the apparatus used in the distillation, and the stirring rods util- 

 lized in the process of cooling. 



Zinc is intimately associated with both the iron and the copper 

 industries. Galvanized iron is used in wire nettings, corrugated 

 roofing, water tanks, etc. Galvanized iron is not produced by 

 electrolytic deposition as the name implies, but by dipping the 

 iron in a bath of molten zinc. The coating of zinc preserves the 

 iron from rusting. It is far better able to withstand the corrosive 

 action of moist air and water than ordinary tinned iron. The 

 film of zinc is heavier than the corresponding film of tin, therefore 

 the protuberances of the sheet iron are more perfectly protected. 



Zinc is used in a large number of useful alloys, especially with 

 copper. English brass consists of 1 part of zinc and 2 parts 

 of copper. Dutch brass, consists of 10 parts of zinc and 5 parts 

 of copper. Muntz metal of 1 part of zinc and 3 parts of copper. 

 Some varieties of bronze, 1 part of zinc, 4 parts of tin, and 95 parts 

 of copper. 



With copper, tin, and antimony, zinc will mix in all proportions. 

 With lead and bismuth the alloys of zinc are of definite propor- 

 tions. The presence of zinc increases both the hardness and the 

 durability of the alloy. 



Zinc is used in the desilverization of lead, also as a precipitant 

 for gold from potassium cyanide solutions. The form used may 

 be sheet zinc, zinc scraps, granulated zinc, or zinc dust. The 

 last form is more widely used than any of the others because it 

 presents a larger surface to the action of the cyanide solutions. 

 Three grains of gold per ton of solution may yield a profit. 

 One-half pound of zinc will completely reduce to the elemental 

 state all the gold in a ton of these dilute solutions. 



