XVII. NON-ELECTROLYTIC PROCESSES. 29;
order to keep this approximatelj coustaDt A is autoniatically raised.
Many arrangements, similar to that used in the Heroult process, have beea successfully employe^ in the electrolysis of fused salts. Thus, for instance, lead is used in order to take up alkali metals, and several models of crucibles have been constructed by Borchers for the preparation of the alkali metala from the fused salts.
Non-electrolytic Processes with Electrical Heating. Cowles' Furnace. — So long ago as 1815 Pepys carried out experiments on the electric cementation of iron (conversion of iron into steel, by allowing carbon to diffuse into the iron at a high temperature). In this process the iron was raised to the necessary temperature by means of an electric current. The brothers Cowles (in 1884) (//) were the first to introduce the extensive applications of the electric furnace. The furnace, named after them, and which is so highly prized in the aluminium industry, has the construction shown in Fig. 51. A
hollow block of fire- f.,g ^^
proof material, A, is
provided with holes, H and Hi, on op^wsite sides; through these pass two movable carbon electrodes, which, at first, are in contact. The crucible is furnished with an iron lid, and gases can escape through an opening, 0, in tliis. The carbon electrodes generally consist of several (9) rods, each 65 mm. in diameter, fastened together, and these, connected by two strong cables to the soiirce of the current, can be moved by means o£ screws. The mixture of alumina (bauxite), wood, charcoal or coke, and copper or iron clippings is placed round the electrodes. At first the contact surface of the electrodes becomes warm, and these are then drawn apart, so that an arc is formed or the current passes through the mixture in contact with the
�� �
