Much has yet to be learned regarding the alloys of metals, because a very small difference in the proportions of the metals employed produces a great difference in the quality of the alloy sought to be obtained. A very interesting paper on this subject (as published in the London Engineer) has recently been communicated to the Manchester (England) Philosophical Society, by F. Grace Cal-vert, F.C.S., and R. Johnson. The object of the authors of this paper was to present something reliable and usefal regarding the hardness of alloys. The process at present adopted for determining the comparative hardness of bodies consists in rubbing one against another, and the one which scratches is held to be the hardest. Thus, for example, when diamond is rubbed against glass, it is found that the former scratches the latter, hence the diamond is justly held to be the hardest.-Every person is familiar with regard to the comparative hardness of these two bodies, but very few are acquainted with the comparative hardness of other bodies, especially metals and their alloys, although a scale of hardness has long been adopted among mineralogists. Messrs. Calvert and Johnson made a series of experiments with pretty large masses of metal to test their comparative hardness; and the following is a most useful table which has been prepared, embracing the results of their investigations :— Names of Metals. Hardness. Cast Iron, . . . 1-000, Steel.....------, Wrought Iron, . . -948, Platinum, .... -375, Pure Copper, . . -301, Aluminum, . . . "271, Silver, . . . 208, Zinc, .... -183, Gold.....-167, Cadmium, . . . "108, Bismuth, . . . '52, Tin, . . . -27, Lead, .... -10. This table exhibits the remarkable fact that cast iron is harder than all the other metals; it was found to be harder than any alloy. Its great resistance to a crushing force—on account of its cohesion and hardness—is well known; hence its superiority for the pillars and walls of buildings, and the journal boxes of heavy stationary shafting—the latter, however, should always be lined with a soft antifriction alloy. It was found that some brasses were harder than any of the metals composing them, and strange to relate, this hardness is due to the softer metal—the zinc. Thus an alloy of zinc 50, copper 49, was in hardness as compared with cast iron -604; while an alloy of copper 66, zinc 33, was only 472 in hardness. The fact was also eliminated that when the quantity of zinc much exceeded 50 per cent of the copper, the brass produced was very brittle. A beautiful brass composed of zinc 50"68, copper 49-32, was made. It contains about 20' per cent more zinc than the brasses of commerce, and yet when carefully prepared it is richer in color, which renders it superior, for many purposes, to commercial brass, also on account of the softness of the latter. We hope American pin manufacturers will take this as a useful hint, because the pins which they now make, although much cheaper than the old "London pins," are far inferior in the quality of metal; they do not seem to have any strength—they bend like a piece of lead wire. The common alloys employed for making journal boxes are much dearer than a brass composed of zinc 50, and copper 56, and yet they are no harder. For heavy bearing boxes an alloy of copper 82-05, tin 12-82, zinc 5-13, is common. Its hardness is -562 as compared J" with cast iron at ],000, and is lower than the brass of -604 hardness, yet its cost is at least [* three times greater. Wai In a series of bronze alloys containing tin \fi and copper, it was found that an excess of tin ^U was the cause of softness, while an excess of :opper, although it is such a malleable metal, is the-cause of brittleness. Thus an alloy of 21-21 copper, and 78-79 tin, is not brittle ; but an alloy of 34-98 copper, and 65-02 tin is very brittle. When the copper is increased to make an alloy of 84-68 copper, and 15-32 tin, the brittleness is removed, and the alloy is very hard ; it is as compared with cast iron at 1,000, -916 in hardness. A composition of 9-73 copper, and 9027 tin, is very soft, being only -83 as compared with cast iron. An excess of zinc in brass increases its hardness, while the very opposite result would be expected, because zinc is softer than copper. In alloys of copper and tin—common bronze— an excess of tin renders the alloy soft, as would be expected, because it is the softer metal. On the other hand, an increased quantity of copper—from but one-third to that of the quantity of tin in the bronze, up until it (the copper) is four times the quantity of tin—renders the alloy brittle, a result which would not be expected, judging from the nature of the metals in their simple conditions. Regarding the quality of alloys of all kinds, much, undoubtedly, depends on the mode, of mixing them; such as the length of time they are kept at a smelting heat, and the length of time in cooling them. Copper is rendered hard by slow cooling, and soft by rapid cooling, while iron possesses the very opposite qualities. Alloys containing copper generally contract and become of greater specific gravity. An amalgam of mercury and tin expands, as do nearly all amalgams. The following binary alloys also expand, namely: bismuth and zinc; bismuth and antimony; lead and tin, and lead and antimony. Therefore these alloys should take the sharp outline of molds, and be eminently adapted for casting small ornaments.
This article was originally published with the title "Alloys of Metals" in Scientific American 13, 39, 310 (June 1858)