154 MODERN SCIENCE READER 



railroad freights, nearness to the consumers, and many 

 other considerations must be taken into account. Alu- 

 minium is certainly destined to become the most important 

 metal next to iron and steel, and, as far as one can now 

 foresee, will always be produced electrochemically. To 

 have accomplished the establishment of this one single 

 industry, would itself have proved the usefulness of elec- 

 trical methods and their importance to chemistry and 

 metallurgy. 



Refining of Metals: Unless metals are of high purity 

 they are usually of very little usefulness. Electrolytic 

 methods enable almost perfect purity to be easily attained, 

 and in addition permit the separation at the same time of 

 the valuable gold and silver contained in small amount in 

 the baser metals. Over $100,000,000 worth of copper is 

 electrically refined every year in the United States; the 

 metal produced is purer than can be otherwise obtained, 

 giving the electrical engineer the highest grade of con- 

 ducting metal, while several million dollars' worth of gold 

 and silver are recovered which would otherwise have to be 

 allowed to remain in the copper. Again, the method is so 

 simple that but a few words are necessary to set it forth 

 in principle. The impure copper is used as one electrode 

 the anode in a solution of copper sulphate containing 

 some sulphuric acid; the receiving electrode the cathode 

 is a thin sheet of pure copper, or of lead, greased. The 

 electric action causes pure copper only to deposit upon the 

 cathode, if a properly regulated current is used, while a 

 corresponding amount of metal is dissolved from the anode. 

 Silver, gold, and platinum are undissolved, and remain as 

 mud or sediment in the bottom of the bath ; other im- 

 purities may go into the solution, but are not deposited on 

 the cathode if the current is kept low. The cost of this 

 operation is small, and the results are so highly satisfac- 

 tory that 90 per cent, of all the copper produced is thus 

 refined. Similar methods are in use for refining other 

 metals; silver, gold, and lead are thus refined on a large 



