TRE ELECTRIC FURlSrACE. 



297 



Engineei-8. According- to this a.stutc imestigator, who seems to have, 

 in a measure, grasped the conditions and general principles necessary 

 to the successful operation of an arc furnace — no mean conception, 

 when one considers the general lack of knowledge on the subject 

 which prevailed at the time (over twenty' years ago) — the advantages 

 in favor of the electric furnace as a source of heat are that, theoretic- 

 ally, the heat obtainable is unlimited; fusion is effected in a perfectlv 

 neutral atmosphere; the operation can be carried on in a laboratory, 

 without much preparation, and under the eye of the operator; and 

 that the limit of heat practically obtainable with the use of ordinary 

 refractory materials is very high, l)ecause in the electric furnace the 

 fusing material is at a higher temperature than the crucible, whereas 

 in ordinar}^ fusion the temperature of the crucible exceeds that of the 

 material fused within it. 



The general principle of the early Siemens arc f ui-nace is represented 

 in tig. 2, in which B is a refractory crucible of plumbago, magnesia, 

 lime, or other suitable material, 

 which may be varied according to 

 the nature of the su}>stance to be 

 dealt with. It is supported at the 

 center of a cylinder or jacket J, 

 ^nd is packed around with broken 

 charcoal, or a similarh' pool' 

 conductor of heat. Being thus 

 isolated, as it were, from the sur- 

 rounding atmosphere, it retains 

 its heat, and very little is lost })y 

 diffusion. The negatiAC electrode 

 consists of a massive carbon rod 

 C passing verticalh^ through the 

 center of the lid of the crucible and free to move vertically therein, 

 though the clearance opening is, for obvious reasons, very small. The 

 rod C is suspended from the lower end of a copper strap S, which 

 conducts the current from it, being attached at its upper end to the 

 curved extremity of a horizontal beam A. The other side of the beam 

 is provided with an adjustable weight W, and carries, suspended from 

 its extremity by a hinged joint, a hollow soft-iron cylinder e, forming 

 the core of the solenoid E. P is a dash-pot arrangement in which the 

 cylinder works, the tendency of E being to raise it out of V against 

 the counteracting force of the weight W, thus lowcM-ing the negative 

 electrode into the crucible. The solenoid winding is connected as a 

 shunt across the two (dectrodes. The positive electrode F, which may 

 be of iron, platinum, or car!)()n, consists of a rod of one or the other 

 of these materials })assing up through the center of the l)ase of the 

 crucible. The furnace was originally' designed by Siemens for the 



