196 BELL SYSTEM TECHNICAL JOURNAL 



In a recent publication ^^ Rohn states that iron, nickel, and copper 

 may be freed of oxygen by dissociation of their oxides during vacuum 

 melting. According to our experiments, however, when tough pitch 

 copper is melted under a pressure even as low as 1 X 10~^ mm. approxi- 

 mately, the oxygen is not removed. After this treatment the material 

 is still embrittled by annealing in hydrogen. This failure of the oxide 

 to dissociate may be reasonably ascribed to a reduction in dissociation 

 pressure caused by solution of the oxide in molten copper. This 

 explanation is supported by the thermodynamical calculations of many 

 workers.^'' Furthermore, as the oxide solution in liquid copper 

 becomes less concentrated, its dissociation pressure is lowered so that 

 removal of the last traces of oxygen by dissociation becomes ex- 

 ceedingly difficult. 



Rohn 25 has reported that magnetic materials, thermocouple metals, 

 metals for vacuum tube parts, metals for sealing through glass, and 

 nickel-chromium alloys for heating elements are being produced 

 advantageously by vacuum melting. He claims, also, that all of the 

 working properties of the nickel -chromium series of alloys are improved 

 by vacuum melting and that alloys containing up to 2)Z per cent 

 chromium can be worked satisfactorily. 



Concerning the economy of vacuum melting, Rohn points out that 

 production by this method is more costly than production by standard 

 methods. He states that vacuum melting increases the cost of metals 

 ten cents a pound when using a four ton furnace and starting with a 

 cold charge. This can be reduced to one or two cents a pound if the 

 vacuum furnace is used only for the final refining treatment of molten 

 charges. This extra cost should be balanced, in many instances, by 

 the improved quality of metal obtained. Rohn's expectations, which 

 seem to be justified, are that alloys can be made by this process for 

 highly important parts such as turbine blades, tubing for superheaters, 

 and aeroplane parts. 



25 Rohn, A. I. M. M. E.—Tech. Publication No. 470. 



26 Ellis, A. I. M. M. E.—Tech. Publication No. 478. Allen, Inst, of Metals, 

 Advance Copy No. 604 (1932). 



