Under more extensive manufacture the metal has been studied at ease, and its physical and chemical properties have been exactly determined. It is silver-white, but little changed by the air, which gives it a slightly bluish tinge—except when it contains iron. Its most striking quality, and one which makes it most suitable for a large number of industrial applications, is its lightness of weight. Its density varies from 2·56, when it is in a molten condition, to 2·71, when its particles have been consolidated by hammering, and its mean density may be put at about 2·60—that is, it weighs about two and a half times as much as water, while steel is nearly three times as heavy, and copper three and a half times, silver four times, and gold nearly eight times; so that four times as many articles can be made from a given weight of aluminum as from the same weight of silver. In many cases one metal may be substituted for the other without inconvenience. While not so hard as gold or silver, aluminum is equally malleable and ductile: it can be beaten into thin pellicles that a breath will blow away, with which objects can be aluminum-coated as they are gilded. It can be drawn into wires finer than a hair, and yet so firm and supple that they can be woven with silk. It is less fusible than zinc and more so than silver, and is easy, therefore, to cast and mold. Although very sonorous, it has not yet been successfully cast into bells, because the repeated strokes of the hammer make it hard and brittle; but the tuning forks made from it are satisfactory to musical artists. The sulphurets, which blacken silver so quickly, are without action on aluminum. Similarly insensible to organic secretions, it lends itself to the making of certain surgical apparatus. Ingenious tubes have been made from it which permit patients who have been operated upon for tracheotomy to breathe, and American dentists have utilized it in the construction of their modern apparatus. It is equally fitted for making into plate and kitchen utensils, for which its specific lightness makes its use convenient. Its conductibility for both heat and electricity authorizes us to predict a fine future for it. It is, it is true, an inferior conductor to gold and silver, about as good as copper, and twice as good as iron; hence an aluminum wire will carry twice as great a quantity of electricity in a given time as an iron wire; or, to carry an equal quantity the aluminum wire need be only half as large; and aluminum being only one third as heavy as iron, it will have to be only one sixth as heavy. These properties should, were the cost equalized, make aluminum vastly more available for telegraphic and other electric wires than iron. Furthermore, aluminum not being acted upon by the air, galvanization, which is necessary for the preservation of iron wire, could be dispensed with.
Aluminum is, however, inferior to iron and steel in tenacity.
