EXPERIMENTS ON THE TRANSVERSE-STRESS AND TOUGHNESS OF BARS OF MANGANESE-BRONZE AS COMPARED WITH WROUGHTIRON AND GUN-METAL; MADE BY DROPPING A WEIGHT ON THE MIDDLE OF BAR RESTING ON SUPPORTS AT EACH END.

(Weight of monkey, 50 lbs.; height of fall, 5 feet; distance between supports, 1 foot; dimensions of bar, 1 inch square, 14 inches long.)

PERMANENT DEFLECTION IN INCHES, IN THE LENGTH OF 12 INCHES.

Gun-metal. The specimens Nos. 1, 2, and 3 were sent from the locomotive works of one of the railways terminating in London, and tested in the presence of an officer of the department, and fairly represent the qualities of gunmetal ordinarily found in such works, and supplied by brassfounders. Nos. 4 and 5 were cast specially and composed of best selected copper, 16 parts, English tin, 2 parts; No. 6 of copper 16 parts, and tin 2 parts by weight.

Mr. Parsons states that, in all the different varieties of his manganese-bronze, the elements are combined in atomic proportions; and he claims that by this means the alloys are finer in texture, more homogeneous, stronger, and of

a much more stable character than when not so combined; thus in the No. 3 quality the addition of per cent tin, instead of making it harder and stronger, as it ought to do, according to the ordinarily accepted ideas, actually makes it softer, weaker, and the grain coarser; and the same thing occurs if the additional tin is increased or 1 per cent, until the tin arrives at another definite atomic proportion, when an alloy of a different character appears; but it then again becomes close-grained, sound, homogeneous, and stable. As a further proof of the soundness of this theory he states that if the No. 3 quality be passed through an ordinary reverberatory furnace, and exposed to the action of an oxidising flame for a considerable time, no appreciable difference is made in the composition of the alloy. The same remarks, in a great measure, apply to Nos. 1 and 2, and although zinc escapes on remelting, it carries with it an atomic complement of copper, so that the proportions of what remains are not disturbed. This appears to be confirmed by the colour of the condensed fumes, which, instead of being white, as they are when produced from zinc alone, have a beautiful pink colour, which may be attributed to the presence of copper.

Another and perhaps still more palpable proof of the value of combining the metals in their atomic proportions, given by Mr. Parsons, is that, when this is done, the specific gravity of these alloys is perceptibly increased over those not so combined, even though in the latter case the heavier metal be in excess. In No. 1 manganese-bronze, which contains a large amount of zinc, and which, judging by its constituents, ought to be a comparatively light metal, was proved to be equal to that of ordinary gun-metal, composed of copper and tin, and very considerably above the mean weight of the metals composing it, indicating that these metals must have combined in such a manner as each to fit into, and fill up the infinitesimal spaces between the molecules of the other, and if not actually forming what chemists would admit to be a perfect chemical compound, certainly

more nearly approaching it than when the metals are mixed together in a haphazard manner.

The stable qualities of manganese-bronze are also due very materially to the action of metallic manganese on copper, by freeing the latter from its oxides, and thus bringing the metals added to it into actual contact, and enabling them to combine in a more perfect manner than would be the case without the presence of a deoxidiser.

ALUMINIUM-BRONZE

§ 78. This is an alloy of copper with aluminium, and is manufactured in different qualities by varying the amount of aluminium, which is generally used in small quantity compared with that of copper. Alloys containing 60 per cent of aluminium and upwards are hard, brittle, and crystalline. With equal quantities of the constituents a soft alloy is obtained, and when the amount of aluminium is less than 30 per cent, the hardness again returns. A very small amount of aluminium in copper reduces its conductivity for electricity considerably. The alloys containing 10 per cent of aluminium downwards are those generally manufactured, and of these the 10 per cent alloy is perhaps the best for all-round properties.

Deville states that 2 to 3 per cent alloys are used by M. Christofle for large castings of works of art. They are harder than aluminium and work well under the "burin" and chisel.

The useful properties of the 10 per cent alloy were first described by M. Debray. It is very hard, can be beaten when cold, but with remarkable perfection when hot, and may be well compared to iron, which it resembles in all these physical properties; it is also very ductile. It behaves as a true alloy, and consequently will not liquate into different combinations. This is proved by the fact that, when in making the alloy, the pure copper is in the crucible, and a bar of aluminium is added; the combination takes

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place with such disengagement of heat that if the crucible is not of good quality it will be fused, for the whole attains a white heat. The colour of the bronze is exactly that of green gold" (an alloy of gold and silver), and it takes a beautiful polish, being comparable in this regard only to steel. Its chemical properties differ but little from those of most of the alloys of copper. However, in numerous experiments it has been found to resist most chemical agents much better than these, especially sea-water and sulphuretted hydrogen. Its tenacity is equal to steel. According to experiments as to its wear in the form of journal boxes, it is said to wear away less than any other journal metal yet tried. Its malleability is almost perfect, as is seen by the following report of M. Boudaret, a practical engineer: First, aluminium-bronze is malleable at all temperatures, from bright red to cold; second, it is perfectly malleable at a red heat, breaking less and elongating more than pure copper; third, it is hard to roll in the cold, after several passes it ceases to elongate, and must then be annealed very often, or it will break quickly; fourth, it results from the foregoing, that it is best to roll it at as great a heat as possible below fusion; annealing and tempering render it softer than simple annealing. If after being annealed at a bright red heat, it is let cool in still air to redness and then plunged in cold water, it is ductile and malleable enough in the cold to stand all industrial working."

These facts were announced some time back by the late Dr. Percy. Messrs. Tissier state that, just as copper increases the hardness of aluminium, so aluminium in small proportions increases the hardness of copper; however, aluminium does not injure its malleability, but makes it susceptible of taking a beautiful polish, and according to the proportions, varies its colour from red gold to pale yellow. The alloys alter much less by successive fusions than the alloys of copper with tin and zinc employed for the same purpose. A 10 per cent aluminium alloy is harder than our gold coin, takes a fine polish by burnishing, and has the colour of pale

jeweller's gold: it can be forged and worked the same as copper. The 5 per cent aluminium alloy is less hard than the preceding, but, like it, takes a fine polish, and in tint approaches nearly to that of pure gold. Alloys with 5 to 10 per cent of aluminium may have their colour changed at will, either by leaving them in nitric acid, which takes away the copper and leaves the aluminium, or in hydrochloric acid, which takes away the aluminium, leaving the copper. The resistance, hardness, and elasticity, which are communicated to copper by introducing small quantities of aluminium, make these important industrial alloys.

Mierzinski states that "two points are to be attended to in making aluminium bronze. First, a pure copper must be used. The best is that electrically deposited, but it generally costs too much. The next best is the Lake Superior brand; the usual commercial copper gives very indifferent results, owing to the antimony, arsenic, tin, zinc, or iron with which it is contaminated. The bronze is deteriorated by being alloyed with zinc or tin. Secondly, the alloy must be remelted two or three times to remove its brittle

In all probability the percentage of aluminium increases by remelting. The usual alloys are those of 1, 2, 5, and 10 per cent aluminium. The 5 per cent bronze is golden in colour, polishes well, and casts beautifully; is very malleable cold or hot, and has great strength, especially after hammering. The 7 per cent bronze is to be recommended as superior to the 5 per cent; it has a peculiar greenish gold colour, which makes it very suitable for ornamental purposes. The 10 per cent bronze has a tenacity of about 100,000 lbs., compressive strength 130,000 lbs., per square inch, and its ductility and toughness are such that it does not even crack when distorted by this load. It is so ductile and malleable, that it can be drawn down under a hammer to the fineness of a cambric needle. It works well, casts well, holds a fine surface under the tool, and when exposed to the weather, it is in every respect