THE ELECTRIC FURNACE. « 



Bv J. Wright. 



There are few inventions in the electrical tield which have benefited 

 the chemist and metallurgist more than that comprised under the gen- 

 eral title of ''electric furnace/' Up to, comparative!}^ speaking, a few 

 years ago the highest attainal)le temperature by any known artificial 

 means was 1,800"^ C, or, possibly, with exceptional facilities and the 

 exercise of great care, as high a temperature as 2,000° C. may, in some 

 cases, have been attained, though the exact limit is questionalde; cer- 

 tainly it does not rise much above the latter figure. Thanks, how- 

 ever, to the indefatigal)le researches of Moissan, Siemens, Borchers, 

 Cowles, and some other investigators, we now possess a means for the 

 artificial production of temperatures far above this limit, which enable 

 us to fuse and otherwise treat commercially such hitherto refractory 

 substances as chromium, platinum, carbon, and even the once inde- 

 structible crystalline form of that element, the diamond. 



Generally speaking, electric furnaces may be divided under two 

 main headings, namely, those in which the heating effect is produced 

 by the electric arc established between two carbon or other electrodes 

 connected with the source of current, connnonly knowni as arc fur- 

 naces; and those in which the heating effect is produced by the pas- 

 sage of the current through a resistance, which either forms part and 

 parcel of the furnace proper, or is constituted, by ft suitably conduct- 

 ing train, of the material to be treated in the furnace. The principle 

 of this latter type is analogous to that involved in the heating to 

 incandescence of the ordinary electric-lamp filament, and such fur- 

 naces are, as u class, known as resistance furnaces. 



The earlier electric furnaces naturally assumed an experimental* 

 form, and of these that devised ])y Moissan, the celebrated chemist 

 and investigator, is probabl}' the simplest. It is an arc furnace, and 

 consists of two chalk blocks bored out at their centers to receive a 

 carbon crucible, which incloses the center or hearth of the furnace 

 proper. Into this cavit}' pass two massive carbon electrodes, through 

 openings provided for them in the walls of the structure, which is 

 held together by massive clamps. Suitable terminal connections to 



"lli'priiited, hy porinission, after revision Ity tin- author, from Cassier's Magazine, 

 June, wo:]. 



SM I!»(I8 20 -'^'^ 



