Page:1902 Encyclopædia Britannica - Volume 25 - A-AUS.pdf/389

 ALVA—ALVERSTONE proportion (O'OOS per cent.) removes oxide, and renders the molten metal more fluid, causing the finished products to be more homogeneous, free from blow-holes, and solid all through. On the other hand, its electro-positive nature necessitates some care in its utilization. If it be exposed to damp, to sea-water, or to corrosive influences of any kind in contact with another metal, or if it be mixed with another metal so as to form an alloy which is not a true chemical compound, the other metal being highly negative to it, powerful galvanic action will be set up, and the structure will quickly deteriorate. This explains the failure of boats built of commercially pure aluminium which have been put together with iron or copper rivets, and the decay of other boats built of a light alloy, in which the alloying metal (copper) has been injudiciously chosen. It also explains why aluminium is so difficult to join with low-temperature solders, for these mostly contain a large proportion of lead. This disadvantage, however, is often overestimated, since in most cases other means of uniting two pieces are available. The metal produces an enormous number of useful alloys, some of which, containing only 1 or 2 per cent. of other itself metals,with combine the lightness of aluAlloys. xninium far greater hardness and strength. Some with 90 to 99 per cent, of other metals exhibit the general properties of those metals conspicuously improved. Among the heavy alloys, the aluminium bronzes (Cu, 90-97’5 per cent.; Al, 2'5-10 per cent.) occupy the most important position, showing mean tensile strengths increasing from 20 to 41 tons per square inch as the percentage of aluminium rises, and all strongly resisting corrosion in air or sea-water. The light copper alloys, in which the proportions just given are practically reversed, are of considerably less utility, for although they are fairly strong, they lack power to resist galvanic action. This subject is far from being exhausted, and it is not improbable that the alloy - producing capacity of aluminium may eventually prove its most valuable characteristic. In the meantime, ternary light alloys appear the most satisfactory, and tungsten and copper, or tungsten and nickel, seem to be the best substances to add. The uses of aluminium are too numerous to mention. Probably the widest field is still in the purification of iron and steel. To the general public it appeals Uses ' most strongly as a material for constructing cooking utensils. It is not brittle like porcelain and cast iron, not poisonous like lead-glazed earthenware and untinned copper, has no enamel to chip off like steel, does not rust and wear out like cheap tinplate, and weighs but a fraction of other substances. It is largely replacing brass and copper in all departments of industry—especially where dead weight has to be moved about, and lightness is synonymous with economy—for instance, in bed-plates for torpedo-boat engines, internal fittings for ships instead of wood, complete boats for portage, motor-car parts, and boiling-pans for confectionery and in chemical works. The British Admiralty employ it to save weight in the Aavy, and the Continental war-offices equip their soldiers with it wherever possible. As a substitute for Solenhofen stone it is used in a modified form of lithography, which can be performed on rotary printing-machines at a high speed. With the increasing price of copper, it is coming into vogue as an electrical conductor for uncovered mains; it is found that an aluminium wire 0T26 inch in diameter will carry as much current as a copper wire 0T00 inch in diameter, while the former weighs about 79 3b and the latter 162 lb per mile. Assuming the materials to be of equal tensile strength per unit of area—hard-drawn copper is stronger, but has a lower conductivity—the adoption of aluminium thus leads to a reduction of 52 per cent, in the weight, a

343

gain of 60 per cent, in the strength, and an increase of 26 per cent, in the diameter of the conductor; a saving in cost of poles is also effected. At present prices (1900) it is already cheaper than copper per unit of electric current conveyed; but when insulation is necessary, the smaller size of the copper wire renders it more economical. Aluminium conductors have been employed on heavy work in many places outside England, notably for a 30,000 volt current in Washington Territory, U.S. A., which is transmitted a distance of over 30 miles, and similar developments are proceeding in England, the earliest being at Northallerton. For telegraphy and telephony, aluminium conductors are in frequent demand, and give perfect satisfaction. Difficulties were at first encountered in making the necessary joints, but they have been largely overcome by practice and experience. Two points connected with this metal are of sufficient moment to demand a few words by way of conclusion. Its extraordinary lightness forms its chief claim to general adoption, yet is apt to cause mistakes when its price is mentioned. It is the weight of a mass of metal which governs its financial value ; its industrial value, in the vast majority of cases, depends on the volume of that mass. Provided it be rigid, the bed-plate of an engine is no better for weighing 30 cwt. than for weighing 10 cwt. A saucepan is required to have a certain diameter and a certain depth in order that it shall hold a certain bulk of liquid: its weight is merely an encumbrance. Copper being 31 times as heavy as aluminium, whenever the latter costs less than 31- times as much as copper it is actually cheaper. It must be remembered, too, that electrolytic aluminium has only been known during the last decade of the 19th century. Samples dating from the old sodium days are still in existence, and when they exhibit unpleasant properties the defect is often ascribed to the metal instead of to the process by which it was won. Much has yet to be learnt about the practical qualities of the electrolytic product, and although every day’s experience serves to place the metal in a firmer industrial position, a final verdict can only be passed after the lapse of time. The individual and collective influence of the several impurities which occur in the product of the Heroult cell is still to seek, and the importance of this inquiry will be seen when we consider that if cast iron, wrought iron, and steel, the three totally distinct metals included in the generic name of “ iron ”—which are only distinguished one from another chemically by minute differences in the proportion of certain non-metallic ingredients—had only been in use for some dozen years, attempts might occasionally be made to forge cast iron, or to employ wrought iron in the manufacture of edgetools. (e. j. r.) Alva, a police burgh and (woollen) manufacturing town of Clackmannanshire (transferred from Stirlingshire, 1891), Scotland, 7 miles E. of Stirling, the terminus of a branch of the North British Railway. Population (1881), 4961; (1891), 5225; (1901), 4624. Alverstone, Richard Everard Webster, 1st Barox, Lord Chief Justice of England (1842 ), was born 22nd December 1842, being the second son of Thomas Webster, Q.C. He was educated at King’s College and Charterhouse schools, and Trinity College, Cambridge; was called to the bar in 1868, and became Q.C. only ten years afterwards. His practice was chiefly in commercial, railway, and patent cases until (June 1885) he was appointed attorney-general in the Conservative Government in the exceptional circumstances of never having been solicitor-general, and not at the time occupying a seat in parliament. He was elected for Launceston in the