180 BELL SYSTEM TECHNICAL JOURNAL 



tensile strength. Lea claimed, also, that the hydrogen had only a 

 slight effect on the resistance of mild steel to impact and repeated 

 stresses. The fracture produced by repeated stresses, however, was 

 abnormal. 



The amount of hydrogen in electrodeposited metals is believed to 

 affect their properties. Schneidewind ^ showed that the hardness of 

 electrodeposited chromium decreases when the metal is heated to 

 approximately 300° C. This decrease could not be caused by re- 

 crystallization of the deposit, for its grain size was not appreciably 

 changed by heating even at 850° C; nor was the decrease caused by 

 the solution of some constituent which had caused precipitation 

 hardening at room temperature, since quenching and aging did not 

 restore the original hardness. Schneidewind believed that the initial 

 hardness was due to the presence of some volatile constituent, probably 

 hydrogen. 



In order to obtain sound castings of copper, it is necessary, in the 

 usual fire refining process, to stop the operation before the oxygen is 

 entirely removed. If the operation is continued further the copper 

 would take up gases from the furnace and unsound castings would 

 invariably be the result. Copper in the tough pitch condition, 

 therefore, contains a nominal quantity of oxygen (0.04 per cent). 

 Although for ordinary uses this product is perfectly satisfactory, when 

 exposed to reducing gases at elevated temperatures, the contained 

 oxygen combines with them to form products which cause embrittle- 

 ment. For use at high temperatures with reducing gases, therefore, 

 copper must be deoxidized. In the past, metallic deoxidizers were 

 added to the copper during the casting operations, but, in order to 

 assure complete deoxidation, an excess had to be added which reduced 

 the electrical conductivity of the finished product. 



Recently, a brand of copper i" has been placed on the market which 

 is said to be kept free from oxygen during melting and therefore 

 needs no deoxidation. This material can be heated in reducing gases 

 without embrittlement, has electrical conductivity comparable to 

 that of electrolytic copper, and is claimed to be tougher and more 

 ductile than fire refined copper and to have better working properties. 



The studies of Tullis " and Rosenhain '^ on the gas removal and 

 grain refinement of aluminum have yielded results which may have 



9 Schneidewind, Trans. A. S. S.T., 19, US (1931). 



'" Oxygen Free High Conductivity Copper, produced by the United States 

 Metals Refining Co. 



"Tullis, Jour. Inst. Metals, 40, 55 (1928); Metal Ind. (London), 34, 339 (1929); 

 Metal Ind. (London), 34, 371 (1929). 



12 Rosenhain, Jour. Inst. Metals, 44, 305 (1931), No. 2. 



