INDUSTRIAL ELECTRO-CHEMISTRY 145 



furnace plants, originally erected for carbide, becoming free 

 for other purposes. In looking for new processes it seems that 

 nothing has more attracted the interest of European electro- 

 metallurgists than the possibilities in the electrometallurgy 

 of iron and steel. Actual success has been achieved in the 

 production of special steels (tool steels, crucible steel). A 

 very great variety of arc and resistance furnaces have been 

 developed for this purpose and in all of them care is taken to 

 prevent contaminations of the bath from the carbon electrodes. 

 Of special interest in connection with this latter point is the 

 use of a resistance furnace, based on the induction principle, 

 the fused steel forming the single secondary turn of a trans- 

 former, no electrodes whatever being used in this case. 



While the above processes are all purely electro-thermic, 

 the most notable example of a combination of an electro- 

 thermic with an electrolytic process is the manufacture of 

 aluminum. The electrolyte from which the aluminum is 

 deposited is a solution of alumina in a bath of fluorides, and 

 its discovery, which made the manufacture of the cheap alumi- 

 num of to-day possible, is due to Charles M. Hall in this coun- 

 try and to P. L. T. Heroult abroad ; both arrived independently 

 of each other at the same solution. By a recent court decision 

 the electro-thermic side of the process was held to be covered 

 by the internal heating patent of Charles S. Bradley. What 

 the electrochemical method of manufacture has done for 

 aluminum is perhaps best indicated by the fact that the price 

 of one kilogram was $250 in 1855, against 50 cents now. The 

 Pittsburg Reduction company has now something like 22,000 

 horsepower in operation for the production of aluminum, and 

 it is evident that the greatest efforts are to be made to push 

 the use of aluminum for all possible purposes. 



Other examples of a combined electrolytic and electro- 

 thermic reaction are the production of metallic sodium b}^ the 

 Castner process of electrolyzing fused caustic soda, and the 

 Acker process of producing caustic and chlorine by electro- 

 lyzing fused sodium chloride with a cathode of molten lead. 



While the Acker process is the latest and one of the most 

 carefully developed processes for the electrolytic production 

 of caustic and bleaching powder, it is by no means the only 



Vol. 7-10 



