SOME CHEMISTRY OF EVERYDAY LIFE 189 



It is a matter of interest to note that the process at present 

 employed for the enormous output of this metal is essentially 

 the same as that invented by Charles M. Hall 1 in 1886. 

 The price of aluminum metal on the market dropped from 

 four dollars per pound to twenty cents per pound as soon 

 as the new process could supply the demand. 



Aluminum ware and utensils are light, durable, and attract- 

 ive. The density of aluminum is only 2.7 while that of 

 iron is about 7.8. The metal neither rusts nor corrodes. 

 The tarnish which dulls the appearance of aluminum 

 kitchen ware should not be scoured off. It is largely an 

 oxide of the metal, and serves as a protective coating. 

 Strong alkalies, such as soda, should not be used in 

 aluminum vessels except to clean them. The metal is 

 acted upon chemically by alkalies, especially in hot strong 

 solutions. Aluminum in a powdered form when mixed with 

 oil serves as a paint for iron surfaces, giving them a cheerful 

 neat appearance as well as protecting them from rust. 



SUMMARY 



In the production of electrical energy in cells by chemical changes, 

 the value of the energy output from a cell depends upon the difference 

 in the degree of chemical change at the two plates. To increase this 

 difference to a maximum one of the plates usually is so chosen that no 

 action at all takes place upon it. 



The plates of a cell must be immersed, or embedded, in an electrolyte 

 whose ions serve as carriers of electrical energy from one plate across 

 to the other thus closing the circuit. The separation of the plates by 

 any considerable thickness of liquid, or by a porous wall such as a cup 

 of earthenware, hinders this action and increases the internal resistance 

 of the cell to the passing of a current. 



Whatever this electrical energy passing along the wire may be, its 

 presence may be detected by its effect upon a suspended magnetic 

 needle such as a magnetic compass. Enough heat may be developed 



1 Hall was then but twenty-two years of age, having graduated the year 

 before from college. ^ 



