l8o METALS USED IN THE HOME 



Aluminium is very widely used for purposes such as the tops 

 of preserve jars, powder boxes, small picture frames, and many 

 useful and ornamental objects. When aluminium is ground 

 and mixed with oil it forms a durable paint which can be 

 spread over other metals as a protection. Cheerful, silvery 

 looking letter boxes, fire signals, lamp-posts, and radiators owe 

 their bright appearance to aluminium paint. The only draw- 

 back to the use of aluminium is its high cost, because it is not 

 cheap, in spite of the fact that it exists abundantly in all parts 

 of the earth. It is expensive because it is always in combina- 

 tion with substances from which it cannot be easily extracted. 

 Common clay is a compound of aluminium, and attempts have 

 been made to obtain aluminium from it, but the process is diffi- 

 cult and has not been commercially successful. The source 

 of most of our aluminium is aluminium oxide. 



The characteristics of metals. If the average person were 

 asked to describe metals, he would doubtless say that they were 

 hard, heavy, opaque substances capable of enduring enormous 

 strain and of being beaten into various shapes, or of being 

 drawn out into fine wire. This definition would be true of the 

 familiar metals, such as gold, silver, copper, and iron, because 

 all of these metals are hard, heavy, and opaque. All of them are 

 also more or less tenacious ; that is, they offer strong resistance 

 to being torn apart and stand great strain before they give way. 



It is the tensile strength of metals which makes them useful 

 in cables, suspension bridges, and large buildings. The familiar 

 metals are all more or less malleable, that is, they can be beaten 

 out by hard blows. Gold can be hammered, or beaten, into 

 sheets less than one hundred thousandth of an inch thick. Iron 

 is not so malleable as gold. All the common metals are also 

 ductile, that is, they can be drawn out into fine wire. Few 

 metals are as ductile as gold, one grain of which can be drawn, 

 out into a thread almost a mile long. 



