304 



THE ELECTRIC FURNACE. 



In a later form (tig. 10) of the Cowles furnace- charging- funnels F F 

 were introduced through apertures in the lid, while the hearth sloped 

 from cither end to the center, at the lowest point of which was provided 

 an outh^t <> for drawing off the molten products. C C are the carbon 

 electrodes; G, the glands containing the shot; and c, the lining of non- 

 conducting charcoal. The funnels F, hy a judicious feeding process, 



provided a means of 

 keeping the resist- 

 y^C, ance of the column of 

 material fairly uni- 

 form at ;U1 points, 

 thus insuring an even 

 distribution of heat 

 Fig. 10. throughout the mass. 



The Cowles furnace for the treatment of zinc ores was also of the 

 resistance type, and is represented by fig, 11, where R is a long c^d- 

 inder of fire clay, mounted in a brickwork setting and surrounded by 

 a jacket of some refractory material J, which is also a ])ad conductor 

 of heat. The inner end of the cylinder \i is effectually closed by a 

 flanged disk of carbon C, which also constitutes one electrode of the 

 furnace, the other taking the form of a plumbago crucible P, the con- 

 vex base of which tits into the outer extremit}^ of the cylinder R and 

 forms a removable seal. Further, by way of an aperture a in the 

 wall of the crucible, the metallic zinc passes over into it by distillation 

 and is collected therein, a chinmey or outlet c serving to carry off' the 

 gases and fumes produced. The charge of broken ziiic ore is, as before, 

 spread evenly along the cylinder, 

 so as to form a semiconducting 

 chain between the two electrodes. 

 The Cowles furnace for the 

 manufacture of aluminum alloys 

 partook of the nature of Bor- 

 chers's furnace, although it had 

 not, strictly speaking, a continu- 

 ous resistance core of its own. 

 Two massive tubular electrodes, 

 provided with a means for manual adjustment, carried close-fitting 

 cores of smaller section, which inclined to one another and actually 

 met, forming a conducting core of high resistance at a point in the 

 center of the furnace immediately under the aperture of the feeding- 

 hopper. These smaller electrodes, together with the raw material fed 

 on to them at the point of meeting, formed a conducting link of high 

 resistance between the main electrodes, and the heating efi'ect of the 

 current was thus localized and confined to the point at which it was 

 most needed, namel}^ at the feeding center of the cavity. 



A circular form of resistance furnace, devised by M. \i. Conley 



Fig. U. 



