Inventors at Work, with Chapters on Discovery

by George Iles

Aluminium and Its Uses.

From Indian handicrafts, developed by aboriginal skill, patience and good taste to remarkable triumphs, let us turn to an achievement of a modern chemist who, calling electricity to his aid, bestowed a new metal upon industry, making possible new economies in a wide sisterhood of arts. Aluminium was discovered in 1828 by Wohler, a German chemist, who noted its lightness, toughness, and ductility. At the Centennial Exhibition at Philadelphia, in 1876, a surveyor’s transit built of aluminium was shown, but the metal at that time was six-fold the price of silver, so that the instrument for some years remained uncopied. Of course, engineers and mechanics were much interested in a metal only about one-third as heavy as brass or copper, of white lustre, and with as much as five-eighths the electrical conductivity of copper. All that hindered the extensive use of the metal was its high cost. If that cost could be lowered, at once copper, and even silver, would face a rival. After many unsuccessful because expensive processes for obtaining the metal had been devised, a method was found at once simple and inexpensive.

This method of separating aluminium from its compounds was devised by Charles M. Hall, while an undergraduate student at Oberlin College, Ohio. His success turned on his knowledge of the properties of related metallic compounds. He recognized the probable value of aluminium in the arts, could it be produced in large quantity at low cost. He believed that electrolysis would prove the most convenient, thorough and inexpensive method; but there was at that time no process known by which it could be applied to this element. His problem was to find a form of electrolyte rich in aluminium which should be comparatively easy to separate into its elements, and to discover a substance for the solvent which should prove a satisfactory bath. This latter substance must, furthermore, be a good conductor of electricity, must readily dissolve the proposed electrolyte, and must have a higher resistance to electrolytic disruption than the electrolyte. To discover the needed substances for electrolyte and solvent involved the examination of all available compounds of aluminium, the study of the various possible solvents for the compound selected, and the determination of electric conductivities. By virtue of rare familiarity with the chemistry and physics of the subject, with the properties of every substance concerned, the search was, after a time, rewarded with complete success. It was found that bauxite—the oxide of aluminium, alumina, in fact—is dissolved by molten cryolite, the double silicate of aluminium and sodium, and that the latter, while dissolving the bauxite freely and serving as an ideal solvent, also itself breaks up under the action of the electric current at a much higher voltage than alumina. So far as known, these are the only substances in nature which stand to each other in such relation as to permit the commercial production of the metal.

Aluminium as constructive material has disappointed some of its earlier advocates. It is difficult to work, gumming the teeth of files and resisting cutting and drilling tools by virtue of the very toughness which makes it desirable for tubes, columns, and the like. Its excellences, however, are manifold: the German army on investigation found that helmets of aluminium, as light as felt, turned the glancing impact of a bullet. For soldiers’ use it now forms not only helmets, but cooking vessels, cartridge cases, buttons, sword and bayonet scabbards. It gives the photographer as well as the surveyor instruments which unite strength with lightness. It has furthermore the quality which has long given value to the lithographic stone of Hohenlofen in Bavaria. Aluminium takes a sketch as perfectly as does the stone, with the inestimable advantages that the metal may be readily curved for a cylinder press, that it is compact and light in storage, while without the brittleness which has made stone so costly a servant to both artists and printers. To produce a deep color from stone it may be necessary to print one impression over another again and again; from aluminium a single impression is enough, as severe pressure may be safely applied.

Aluminium has so great an affinity for oxygen as to play a conspicuous part in the metallurgy of other metals. In the casting of iron, steel or brass, the addition to each ton of two to five pounds of aluminium greatly improves the product; the aluminium by combining with the occluded gases reduces the blowholes and renders the molten metal more fluid and therefore more homogeneous. A second use for aluminium turns on the same quality; it was devised by Dr. Goldschmidt for producing high temperatures, and is especially useful in welding steel rails and pipes. A mixture of iron oxide and aluminium finely divided is ignited by a magnesium ribbon; a very high temperature results as the aluminium combines with the oxygen derived from the iron oxide.

Aluminium by reason of its lightness occupies a large field in naval and military equipments, in motor-car construction, and the like, where the reduction of weight is of paramount importance. For cooking utensils the use of aluminium is constantly extending; the metal is a capital conductor of heat, is not liable to deteriorate in use, and gives rise, if dissolved, to harmless compounds. The chief objection to aluminium is its low tensile strength, which, for the cast metal is only 10,000 to 16,000 pounds per square inch. An improvement is effected by adding as an alloy a small quantity of some other metal, such as nickel or copper. When one part of aluminium is joined with nine parts of copper we have aluminium bronze, the strongest and handsomest of copper alloys, much resembling gold in its lustre.

Aluminium is finding acceptance as an electrical conductor. An installation of this kind in Canada unites Shawinigan Falls with Montreal, 84.3 miles distant. Three cables are employed, each composed of seven No. 7 wires. The total loss in the transmission of 8,000-horse power, at 50,000 volts at the generating station, is about eighteen per cent. Comparing equal conductors, in round numbers the cross-section of an aluminium cable is one-and-a-half times that of a copper cable, the weight being one-half and the tensile strength three-quarters. Everything considered when aluminium is 2¹⁄₁₀ the price of copper, the investor is equally served by both metals as conductors. This is true only where the conductors are bare. Where insulated cables are needed, the increased diameter of an aluminium conductor entails extra cost for insulating material.