ALUMINIUM 179 



for bronze is simply a mixture of copper, tin, and zinc. Brass 

 is a mixture of copper and zinc ; and pewter, a mixture of lead 

 and tin. 



Pure metals are rarely used. Pure gold is so soft that it 

 cannot endure constant use. An i8-carat ring is not pure gold, 

 because one fourth of it is copper, but it is the purest gold which 

 is consistent with daily wear. The best grade steel contains a 

 little nicker for added hardness. Motor boats, steam turbines, 

 and torpedo boats are not made from ordinary steel, but from 

 steel alloyed with nickel. The silver coins which serve as money 

 are alloyed with copper for hardness. 



Aluminium. One of the most important metals to the modern 

 housewife is aluminium, because it is made into silvery pots 



FIG. 64. Lightweight camp cooking outfit for Boy Scouts. 



and pans that are light, durable, and attractive (Fig. 64). 

 Aluminium cooking utensils are serviceable and safe, as well as 

 attractive, because they do not rust or corrode, and are not 

 affected by dilute vegetable acids. Pure aluminium is acted 

 upon by acids, but aluminium which has been exposed to the 

 air acquires a dull coating of aluminium oxide which is not af- 

 fected by acids. Aluminium cooking utensils should not be 

 polished or cleaned with anything which wears off the protec- 

 tive coating. Soap and water clean aluminium sufficiently. 



CLARK INTRO. TO SC. 12 



