230 INDUSTRIAL MINERALS DIAGRAM 19 



Zinc ore. This is also called blende. It is pulverised and 

 calcined with, coal to obtain zinc. As this metal is volatile, 

 that is, is liable to be reduced to a state of vapour by the action 

 of the fire, advantage is taken of this quality to purify it. The 

 rough zinc is distilled out of contact with air, and distils over 

 and condenses in drops. It must then be remelted. Zinc, like 

 iron, can be hammered into thin sheets, which are much used in 

 industry to cover houses, and to make pails and other utensils. 



A colour called zinc white is also made with this metal, which 

 unlike white lead is not dangerous to those who employ it. 



Tin ore. This ore is much less widely distributed than that of 

 many metals, but it is very abundant in Cornwall. It is a very 

 valuable metal. When pure, it is as white as silver, but quickly 

 tarnishes. It is quite harmless, and communicates no injurious 

 property to water. For this reason it is used to line copper ves- 

 sels. It is also used to make galvanised iron, which is only a thin 

 layer of sheet-iron tinned on both sides. If thus prepared, the 

 iron does not rust as long as the layer of tin covering its surface 

 is not worn off or removed. Tin is also used to make the solder 

 used by plumbers, and the tin-paper in which chocolate and 

 other substances that damp would injure are sometimes 

 wrapped. 



Lead ore. To obtain lead, the ore must first be roasted several 

 times, and the residue must then be mixed with coal and old 

 iron, and heated, when the lead melts, and runs out. It is bril- 

 liant, like tin, when cut, and has a bluish reflection, but imme- 

 diately tarnishes in the air. However, it is nearly unalterable. 

 It makes an excellent covering for houses, and is also extremely 

 useful for making gas-pipes and water-pipes. 



However, lead is sometimes a dangerous metal, and may com- 

 municate a poisonous property to beverages. Beverages, such 

 as wine or cider, ought not to be placed in leaden vessels, or they 

 will be liable to produce colic in those who drink them. 



White Lead, red lead, or minium, and litharge, are all com- 

 pounds of lead, and the painters who use these colours are conse- 

 quently liable to be attacked with colic. In many cases oxide of 



