252 GENERAL SCIENCE 



properties make it the best metal for a large variety of 

 uses. (Figure 222.) 



Cast iron contains from four to five per cent of carbon 

 and other impurities. These impurities lower the melt- 

 ing point of cast iron to about 1200 C., and they also 

 make the iron very hard and brittle. 



Wrought iron is nearly pure iron. To make wrought 

 iron, cast iron is remelted with another iron ore, hema- 

 tite, and stirred until the impurities have been removed. 

 Because of its extreme toughness, wrought iron is quite 

 valuable. It is used for chains, wire, bolts, etc. It 

 melts at a much higher temperature than cast iron, and 

 for this reason is used for fire bars. 



Steel has some carbon in it, but not so much as cast 

 iron. It can be tempered to different degrees of hardness. 



Copper. Copper has a characteristic dull red color 

 when exposed to the air. It melts at about 1050 C., is 

 a good conductor of heat and electricity, and is quite 

 malleable. It was one of the first metals used by man. 

 This was because it was found in a free state and did not 

 need to be separated from ore and also because it is so 

 easily hammered into desired shapes. (Figure 223.) 



Copper is used for electric wiring, for evaporating pans 

 and some cooking utensils, for sheathing ships, and for 

 places on buildings where a metal is needed that will 

 resist weathering. Brass is an alloy of copper and zinc, 

 and bronze is an alloy of copper and tin. 



Mercury. Most of the mercury of commerce comes 

 from California and Spain. At ordinary temperatures it 

 is a liquid. It solidifies at - 40 C. and boils at 357 C.- 

 It has a silvery, metallic luster which is not affected by 

 air and water. Mercury has a number of commercial 

 uses. It is used in thermometers and barometers. In 



