Engineering Wonders of the World
Volume III

THE KINLOCHLEVEN ALUMINIUM WORKS. 273 sively for the transmission of high-tension current, especially in America. To take a couple of instances : alumin- „ , lum conductors deliver current Conductors. from the generating station at Snoqualmie Falls to Tacoma, 44 miles away ; and from Electra to San Francisco, 154 miles. Spans are made longer with aluminium than SKETCH MAP SHOWING THE BLACKWATER DAM, THE CONDUIT, THE PIPE TRACK, AND THE FACTORIES. The broken line shows the route of the cableway used for transporting material from the loch to the Dam site. the this and well has with copper conductors — one across Niagara River is of 2,192 feet—and effects a considerable economy in poles standards. For underground insulated cables a as fo overhead conductors aluminium a future before it. When one considers the enormous development of electrical power schemes, and the fact that the cheapening of conductors will hasten that development, the importance of aluminium among metals is sufficiently established on this head alone. The electrical method of reduction consists, to describe it briefly, of subjecting pure oxide of aluminium—alumina—to the intense heat of an electric furnace. The _ furnace is an iron box lined Furnace. . m . with carbon. To an iron plate at the bottom is attached the cathode, or negative pole, of the dynamo. The positive pole is a bundle of carbon rods so arranged that they can be moved vertically. Cryolite is fed into the cell and melted, and then the (1,408) alumina is introduced. The current passes from one pole to the other through the cryolite and alumina, encountering a resistance which develops an exceedingly high temperature, and by electrolytic action causes the alumin- ium to separate and sink through the liquid cryolite to the bottom of the furnace, whence it is drawn off. The alumina used is prepared by drenching a substance called bauxite with a solution of caustic soda. This chemical combines with the alumina to form spdium aluminate, which is subsequently treated with hydrated alumina. The hydroxide, when dried, is ready for the furnace. As the electric furnace requires a large vol- ume of current, the latter must be obtain- able at a low cost to render the manufacture of the metal profitable. The huge power-stations at Niagara Falls, where electrical energy is generated on so large a scale that current is remarkably cheap, have led to the concentration round the Falls of great alu- minium factories, and have made the district the chief world-centre of the aluminium in- dustry. In the British Isles manufacturers have been handicapped by lack of natural water-power. We have no waterfalls over which a sufficient volume of water passes at all times of the year to work power plants VOL. TIL Need for Cheap Current. 18