260 THE ADDRESSES, LECTURES, ETC., OF 



Experiments with long solenoid coils have shown that the attractive 

 force exerted upon the iron cylinder is subject only to slight variation 

 within a length of several inches, which circumstance allows of a 

 working range to that extent of nearly uniform action on the 

 electric arc. 



This automatic adjustment of the arc is of great importance to 

 the attainment of advantageous results in the process of electric 

 fusion ; without it the resistance of the arc would rapidly diminish 

 with increase of temperature of the heated atmosphere within the 

 crucible, and heat would be developed in the t dynamo-electric 

 machine to the prejudice of the electric furnace. The sudden 

 sinking or change in electrical resistance of the material under- 

 going fusion would, on the other hand, cause sudden increase in 

 the resistance of the arc, with a likelihood of its extinction, if such 

 self-adjusting action did not take place. 



Another important element of success in electric fusion consists 

 in constituting the material to be fused the positive pole of the 

 electric arc. It is well known that it is at the positive pole, that 

 the heat is principally developed, and fusion of the material con- 

 stituting the positive pole takes place even before the crucible itself 

 is heated up to the same degree. This principle of action is of course 

 applicable only to the melting of metals and other electrical con- 

 ductors, such as metallic oxides, which constitute the materials 

 generally operated upon in metallurgical processes. In operating 

 upon non-conductive earth or upon streams of gases, it 

 becomes necessary to provide a non-destructible positive pole, such 

 as is supplied by the use of a pool of fused platinum, or iridium, 

 or by a plumbago crucible. In working the electric furnace, some 

 time is taken up in the first instance in raising the temperature of 

 the crucible to a considerable degree, but it is surprising how 

 rapidly an accumulation of heat takes place. In using a pair of 

 dynamo-machines capable of producing seventy webers of current 

 with an expenditure of 7-horse power, and which, when used for 

 purposes of illumination, produced a light of 12,000 candles, a 

 crucible of about eight inches in depth, immersed in a non- 

 conductive material, has its temperature raised to a white heat in 

 fifteen minutes, and 4 Ibs. of steel are fused within another 

 fifteen minutes, successive fusions being effected in somewhat 

 diminishing intervals of time. The process can be carried on on 



