296 



thp: electric furnace. 



the car)>oii rods jiro prt)vided. exterior to the furnuee, :nid tlie arc 

 e.stabli.slied between their inner extremities when the current is turned 

 on plays over the center of the crucible, h(^ating its contents. 



A furnace of this type, though its capacity is limited to a single 

 charge t)f the cruci])le at each operation, has nevertheless proved 

 itself of extreme utility in laboratory ])ractice, and is a very efficient 

 source of heat in that the hearth or center of activity is entirely sur- 

 rounded by refractory, nonconducting walls. Yeiy little heat is, 

 consequently, lost by difiusion or radiation. 



A somewhat more elaborate modification of Moissan's original fur- 

 nace has been devised by Messrs. Ducn^tet & I.,ejeune, of Paris, and is 

 shown in fig. 1. It consists of a refractorv chani])er R, ])uilt of fire 

 brick or some other suitable material, and provided with an opening 

 A, through which the substances to ])e treated may be introduced. C C 

 are carbon rods supported in massive tubular clamps T T, which are 

 water-jacketed to keep down their temperature to a safe limit. 1) is a 

 carbon or magnesia crucible, forming the hearth of the furnace and 

 containing a ciiarge of the material to be treated, while W is a remov- 



able window or inspection opening, fitted with rid)y glass, through 

 which o])erations re((uiring only a moderate heat can be watched 

 while in progress. When utilized for higher temperatures, this glass 

 slide is replaced 1»y a slab of refractory material, such as fire l)rick. 

 The carbons C C project through the walls of the furnace at right 

 angles to each other, and the necessary separation of their inner 

 extremities for the establishment of the arc takes place at a point just 

 above the mouth of the crucible B, as shown. A system of tubes leads 

 into the interior of the chamber K, and serves, when required, for the 

 introdtiction of special gases with which it may be necessar}' to cause 

 the contents of the crucibl(> to enter into chemical com})ination. A 

 horseshoe permanent magnet M, manipulated at the exterior, exerts a 

 repellant force upon the arc, directing it down into the crucible as 

 desired, after the manner of a blowpipe. 



Sir William Siemens was the first to apply the electric arc furnace 

 to conunercial operations, and his apparatus and experiments were 

 described in a paper read by him before the Society of Telegraph 



