for this purpose is electric light carbon, as it possesses the necessary amount of electrical resistance, and is capable of enduring any known degree of heat when protected from oxygen without disintegrating or fusing; but crystalline silicon or other equivalent of carbon can be employed for the same purpose.  This is pulverized or granulated, the degree of granulation depending upon the size of the furnace.  Coarse granulated carbon works better than finely pulverized carbon, and gives more even results.  The electrical energy is more evenly distributed, and the current can not so readily form a path of highest temperature, and consequently of least resistance through the mass along which the entire current or the bulk of the current can pass.  The operation must necessarily be conducted within an air-tight chamber or in a non-oxidizing atmosphere, as otherwise the carbon will be consumed and act as fuel.  The carbon acts as a deoxidizing agent for the ore or metalliferous material treated, and to this extent it is consumed, but otherwise than from this cause, it remains unimpaired.

Fig.  I. of the accompanying drawings is a vertical longitudinal section through a retort designed for the reduction of zinc ore, according to this process, and Fig.  II. is a front elevation of the same.  Fig.  III. is a perspective view of a furnace adapted to withstand a very high temperature, and Figs.  IV. and V. are respectively longitudinal and transverse sections of the same.

[Illustration:  THE COWLES ELECTRIC SMELTING PROCESS.]

This retort consists of a cylinder, A, made of silica or other non-conducting material, suitably embedded in a body, B, of powdered charcoal, mineral wool, or of some other material which is not a good conductor of heat.  The rear end of the retort-cylinder is closed by means of a carbon plate, C, which plate forms the positive electrode, and with this plate the positive wire of the electric circuit is connected.  The outer end of the retort is closed by means of an inverted graphite crucible, D, to which the negative wire of the electric circuit is attached.  The graphite crucible serves as a plug for closing the end of the retort.  It also forms a condensing chamber for the zinc fumes, and it also constitutes the negative electrode.  The term “electrode” is used in this case as designating the terminals of the circuit proper, or that portion of it which acts simply as an electrical conductor, and not with the intention of indicating the ends of a line between which there is no circuit connection.  The circuit between the “electrodes,” so called, is continuous, being established by means of and through the body of broken carbon contained in the retort, A. There is no deposit made on either plate of the decomposed constituents of the material reduced.  The mouth of the crucible is closed with a luting of clay, or otherwise, and the opening, d, made in the upper side of the crucible, near its extremity, comes entirely within the retort, and forms a passage for the zinc fumes from the retort chamber into the condensing chamber.  The pipe, E, serves as a vent for the condensing chamber.  The zinc ore is mixed with pulverized or granular carbon, and the retort charged nearly full through the front end with the mixture, the plug, D, being removed for this purpose.