The 10 per cent. bronze may be forged cold, and becomes extremely dense under the action of the hammer. The blades of dessert-knives are thus treated in order to give them the requisite hardness and elasticity. But it has another valuable quality which is found in no other kind of brass or bronze: it may be forged hot, as well as, if not better than the very best iron. It thus becomes harder and more rigid, and its fracture shows a grain similar to that of cast steel. On account of the hardness of the aluminum bronze, rolling it into sheets would be a tedious and expensive process, were it not for this property of being malleable at a red heat. But it may in this manner be rolled into sheets of any thickness or drawn into wire of any size. It may also be drawn into tubes of any dimension.
From several experiments made at different times at Paris, it appears that the breaking weight of the cast bronze varies from 65 to 70 kilogrammes the square millimetre. The same bronze drawn into wire supported a weight of 90 kilogrammes the square millimetre. The iron used for suspension bridges, tested in the same manner, did not show an average of more than 30 kilogrammes. Some experiments were also made by Mr. Anderson, at the Royal Arsenal at Woolwich, in England, who tested at the same time the aluminum bronze, the brass used for artillery and commonly called gun metal, and the cast steel made by Krupp in Prussia. Taking for the maximum strength of the bronze the lowest of the numbers found as above, we are thus enabled to form the following table of comparative tenacities:
| Aluminum bronze 10 per cent. | 65 |
| Crupp’s Cast Steel | 53 |
| Refined Iron | 30 |
| Brass for cannon | 28 |
The comparative toughness of these same four metals was also tested in the following manner: A bar of each was prepared of the same size, and each bar was then notched with a chisel to precisely the same depth. The bars were broken separately, upon an anvil, by blows from a hammer. The last three metals in the table broke each at the first blow, with a clean and square fracture. The aluminum bronze only began to crack at the eighth blow, and required a number of additional blows before the two pieces were entirely separated. And the irregular, torn surface of the fracture showed the peculiarly tough and fibrous nature of the metal.
The elasticity of the aluminum bronze was tested by M. Tresca, Professor at the Conservatoire des Arts et Métiers. The experiment was made upon a bar of simple cast metal, and the following is his report: “The coefficient of elasticity of the aluminum bronze, the cast metal, is half that of the best wrought-iron. This coefficient is double that of brass and four times that of gun metal, under the same conditions.”
The specific gravity is 7.7, about the same as iron. Another very valuable quality is presented in the fact that it is acted on by atmospheric influences less than are silver, brass, or bronze. This places it in the same rank with gold, platinum and aluminum.
Very stiff and very elastic, tougher than iron, very little acted upon chemically, and in certain cases not at all, capable of being cast like ordinary bronze or brass, forged like iron and steel, of being worked in every way like the most malleable metals or alloys, having, added to these properties, a color analogous to that of the most precious metal, this bronze proves itself adapted to uses almost innumerable. At first sight, it seems difficult to admit that the relatively small proportions of aluminum which enters into the composition of this bronze can be sufficient to modify so extraordinarily the properties of the copper which constitutes so large a portion of its weight. But we must remember that the specific gravity of aluminum is very low, and that a given weight of this metal possesses a bulk four times as large as the same weight in silver. It follows from this that the ten per cent. of aluminum contained in the bronze equals in bulk forty per cent. in silver.
The specimens of the ware we have seen, such as spoons, forks, cups, watch-cases, etc., are certainly very beautiful, having the color and high polish of gold, while dilute acids do not affect the surface.