Aluminum in itself would be of but little use, so that a brief description will be all that is necessary. It is about the color of silver, but susceptible of a higher polish, especially on a fresh-cut surface; it is much less susceptible of oxidization than silver; its specific gravity is but little more than pine wood, and its tenacity, ductility, and laminating qualities are nearly equal to silver. Its use in the mechanical arts is limited, notwithstanding all these qualities, from the fact of its low point of fusibility, and at the heat of the fusible point being easily oxidized, so much so as to prevent soldering, except by an autogenous process. But aluminum does possess a property peculiar to itself--that of forming a purely and strictly _chemical alloy_ with copper. It unites with it in any proportion; the compound formed by the addition of 10 per cent. of aluminum to 90 per cent. of copper has been found to possess all the properties of an entirely new metal, with qualities that render it a very valuable material in all fine work, such as astronomical instruments; and very fine machinery, such as watch-lathes, etc. The French reports on the alloy are somewhat voluminous, but we give the following. The color of this bronze so closely resembles that of 18 carat gold, such as is used for the best jewelry and watch-cases, that it is capable of receiving the highest polish, and is far superior in beauty to any gilding. Samples taken from different parts of the largest castings, when analyzed, show the most complete uniformity of composition, provided only that the two metals have originally been properly mixed while in a state of fusion. These experiments have been made upon cylinders weighing many hundreds of pounds, and are entirely conclusive. This valuable quality is not found in any of the more ordinary alloys of copper. The alloy of copper with tin, for example, known as _gun metal_, is notoriously subject to a phenomenon known as _liquation_; in consequence of which a great difference is found in the composition of the same casting, both in the top as compared with the bottom, and in the centre as compared with the circumference. This phenomenon often causes great inconvenience, as the different parts of large objects will in consequence vary greatly in hardness as well as in strength. In casting artillery the difficulty becomes a serious one, and no means have yet been discovered by which it can be entirely removed.