I INDUSTRIAL ELECTRO-CHEMISTRY 143 



changed into chemical energy and is stored up in this form 

 in the chemicals produced. 



In other words, if an electrochemical process requires the 

 expense of an appreciable amount of electrical energy, then 

 the products of the process possess a higher content of chem- 

 ical energy than the starting materials. This explains why 

 electrochemical methods give us substances of strong chemical 

 affinity. Moreover, these substances represent in a sense a 

 storage of energy, which at the same time enables one to ship 

 readily the stored energy to a point where it may be wanted. 

 Two examples may explain this. 



Aluminum does not occur free in nature and its separa- 

 tion from its compounds requires a considerable amount of 

 energy. It we electrolyze aluminum oxide dissolved in a 

 bath of fluorides, we get aluminum and oxygen; the forma- 

 tion heat of AI0O3 is 392,600 calories; hence, according to 

 Thomson's rule (which is fully good enough for this purpose) 

 we must apply at least 2.8 volts at the terminals of the cell. 

 This voltage, multiplied by the coulombs passed through the 

 cell, represents the electrical energy which is changed into 

 chemical energy. That is what Hall does in producing alumi- 

 num in his cell. Now, we may ship the aluminum somewhere 

 and may then allow it to combine again with oxygen to form 

 back AI2O3. Then we get back our energy in the form of 

 most intense heat. This is what Goldschmidt does in his 

 thermit process. (Of course, he loses the energy which is 

 required to reduce the iron oxide in the thermit; but this is 

 small, compared with the formation heat of AI0O3.) 



In the Union Carbide works in Niagara the energy of the 

 falls after conversion into electrical energy, is stored in form 

 of chemical energy in calcium carbide. As long as we keep 

 it separate from water, the calcium carbide represents a stor- 

 age of a distinct amount of energy. We can afterwards use 

 it for the production of energy by generating acetylene from 

 the carbide and water and using the acetylene for lighting; 

 and we may do this anywhere, since the carbide can be easily 

 shipped. 



These two examples, while simply given to illustrate the 

 energy point of view, are also suggestive as to what we may 



