FACTORS AFFECTING MAGNETIC QUALITY 



259 



carried out in a controlled atmosphere. High-frequency currents (usually 

 1,000 to 2,000 cycles/sec but sometimes much higher) are passed through 

 the water-cooled copper coils, and the alternating magnetic field so produced 



Fig. 11— .-^rc luniace lor large Lumiiicrcial nit-lls. CoiulcbV ul" J. S. Marsh of the Bethle- 

 hem Steel Company. 



heats the charge by inducing eddy currents in it. Crucibles are usually com- 

 posed of alumina or magnesia. 



On a commercial scale melts of silicon-iron are usually made in the open 



