400 THE POPULAR SCIENCE MONTHLY. 



the quality of resisting the forces of pulling, "bending, and twist- 

 ing, which tend to break the metal or separate its molecules. 

 Equal volumes of aluminum and cast iron have about the same 

 power of resistance to these actions. That of copper is not quite 

 double, but that of wrought iron is more than three times, and 

 that of steel about five times as great. For purposes, therefore, 

 where this quality is demanded, aluminum offers no advantages ; 

 but there are numerous other uses in which the question of a 

 greater or less resistance is of no interest ; and the other qualities 

 of aluminum its ductility, conductibility, and lightness may be 

 dominant reasons for employing it. Its use has hitherto been lim- 

 ited by the consideration of cost. 



This difficulty is fast passing away as improved processes are 

 applied, and the use of aluminum has been greatly extended and 

 diversified since Sainte-Claire Deville exhibited the first manu- 

 factured specimen. In 1856 it cost one hundred and eighty dol- 

 lars a kilogramme ; the next year Deville was able to prepare it at 

 La Glaciere under more favorable conditions, and the price fell 

 to sixty dollars. A year afterward the factory was removed to 

 Salindres, where fuel and bauxite were within convenient reach. 

 The price gradually fell ; cryolite, a new aluminum mineral, dis- 

 covered in Greenland, was introduced, and the metal cost only 

 eighteen dollars a kilogramme in 1883. The manufacture was 

 undertaken at several places in England, with improved processes 

 based on the method of Sainte-Claire Deville. Mr. Castner devised 

 a method of producing sodium by which the cost of that metal was 

 largely reduced, and the price of aluminum suffered another fall. 

 Then Mr. C. Netto devised a direct process for producing sodium 

 by exposing pulverized caustic soda to the action of incandescent 

 charcoal, and the cost of aluminum fell to seven dollars a kilo- 

 gramme. 



The brightest promises for the future of aluminum are offered 

 through the electrical processes. When the flame of the voltaic 

 arc is turned upon a mixture of pulverized mineral and charcoal 

 a fusion takes place, and the metal, relieved by dissociation, flows 

 out fluid, limpid, and brilliant. So fine a result, however, can be 

 obtained only under the most favorable conditions, to secure 

 which, not always with certainty, great pains are required. An 

 easier process is to turn the voltaic arc, not upon the pulverized 

 mixture, but upon a bath of mineral substances which have been 

 previously brought to a condition of igneous fusion, as is done 

 in the Cowles electrical process. Complex phenomena are then 

 produced, both calorific and chemical. Important factories have 

 been established for obtaining by this process both pure alu- 

 minum and its alloys with other metals, particularly with iron 

 and copper. By it the company at Pittsburg obtained almost 



