302 



THE ELECTRIC B^URNACE. 



Fig. 8. 



The Henriveiix furnace, for the manufacture of glass, consists of 

 three steps or slabs of refractory material, forming a species of cascade, 

 the mixture to be fused being fed from a hopper onto the top step, 

 whence it descends by gravity over the remainder. The heat from a 

 powerful arc is directed upon each of the three steps, and the mass, in 

 passing through the series of three, emerges finally in a molten state, 

 and is collected in a suitable receptacle at the bottom, where it is main- 

 tained in a state of fusion by a gas or coke fire. It is said to be a very 

 wasteful process in that a considerable quantity of the heat developed 

 in the arcs is lost or dissipated without performing useful work. 



Passing now to resistance f ur- 



^•- -^ naces, Borchers's is typical of 



that class in which a core, form- 

 ing part of tlie furnace itself, is 

 heated by the passage of the cur- 

 rent through it, and imparts its 

 heat to the surrounding mass of 

 material contained in the furnace. It is represented in fig. 8, and 

 consists of a l)lock B of refractory material, through the center of 

 which passes an opening R, forming the crucible or center of activity 

 into which is fed the material to be treated. This space R is- bridged 

 bv a thill carbon rod t\ which is attached at its extremities to two 

 massive carbon electrodes C C, passing through the walls of the 

 furnace and fed with current througli the large metal clamps M. 

 These massive electrodes serve to conduct the current without undue 

 heating to the smaller rod c, through Avhich it passes in turn, rais- 

 ing it to a very high temperature, owing to the resistance ofl'ered to 

 its passage bv a conductor of considerably smaller cross section, and 

 forming, as it were, a central, 

 heated axis to the material con- 

 tained in the crucible. It thus 

 diffuses its heat throughout the 

 mass from its center outwards. 

 The Gibbs resistance furnace 

 is based on the Borchers prin- 

 ciple, a carbon rod, or rods, of small section l)eing supported l)etween 

 massive carbon blocks set in cast-iron sockets let into the brickwork. 

 The novelty of this invention, however, lies in the position of the 

 small resistance rods. These are located above the furnace charge 

 and do not come into actual contact with it at all, the heat l)eing 

 communicated by reflection from the domed roof. 



The Acheson furnace for the manufacture of carborundum is a 

 somewhat rudimentary device, in that it is built up and pulled down 

 again for each charge of raw material dealt with. It is represented in 

 diagram by fig. 9, in which F is a rough fire-brick structure, through 



