SHEET METALS 445 



the aluminum goes to the negative pole and is collected in 

 the molten state. 



Pure aluminum is acted upon neither by the oxygen of 

 the air, by water, nor by dilute acids, but the commercial 

 grade is impure and is rapidly oxidized by steam at a high 

 temperature. Dilute or concentrated sulphuric or nitric 

 acid does not, when cold, act on aluminum, but when heated 

 dissolves the metal rapidly. Dilute or concentrated hydro- 

 chloric acid also will dissolve the metal readily. Since it 

 is not affected to any great extent by organic acid, and the 

 salts of aluminum are quite harmless, this metal is widely 

 used for cooking purposes in place of tin and copper. Caus- 

 tic alkalies readily dissolve aluminum with a formation of 

 aluminates and the liberation of hydrogen. 



Aluminum in a pulverized condition is gray in color, is 

 very malleable and ductile, and has a specific gravity about 

 that of glass (2.7). It melts at a red heat and vaporizes at 

 a very high temperature. 



516. Aluminum Alloys. Aluminum is used to make 

 alloys of various kinds, the most important of which is 

 aluminum bronze. This alloy is made up of from 5 to 8% 

 aluminum and from 92 to 95% copper. It is used to 

 imitate gold, is very rigid and strong, and is not affected 

 by air or water. Hence it is valuable for many purposes. 

 Just before it is poured from the cupola, steel from which 

 castings are to be made has added to it small quantities of 

 aluminum and bronze. This insures that the castings will 

 be free from blow-holes. Lately, a new flash-light powdsr 

 containing aluminum has been placed on the market. 



517, ^ Pses of Tin. Jin i$ obtained from the ore oxide 



