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excess of the required quantity be added, such phosphorus will unite with the alloy, and may become a source of weakness instead of strength. Some metallurgists have thought that the beneficial action of phosphorus is due to its combination with the copper and tin, but such is not probably the case, since, if more than a small quantity be added, the metal is hardened at the expense of toughness; but the alloy still possesses considerable tenacity, and, for special purposes, may be useful. Also, as mentioned above, chemical analysis proves that the strongest bronzes contain only minute quantities of phosphorus. Montefiori-Levi and Künzel, who introduced phosphor-bronze as a material to be used in construction in 1871, state that, besides the deoxidising influence of phosphorus on metals, it performs another very important function. In many copper-tin alloys the copper forms the only crystallised constituent, tin crystallising with great difficulty; and the alloy, in consequence of the different physical condition of the two metals, is not as solid as it would be if both the components were crystallised. Phosphorus has the power of imparting to tin a crystalline nature, which enables it to form with copper a more intimate union, and thus produce a more homogeneous alloy.

If more phosphorus be used than is necessary for the purpose of deoxidation of the metals, the resulting body may be considered an alloy of crystallised phosphor-tin with copper. The question of producing various qualities of phosphorbronze depends not so much upon the quantity of phosphorus as upon the correct proportioning of the various ingredients. The alloys are generally prepared by adding a specially prepared phosphor-copper or phosphor-tin (both these metals being sometimes used at the same time) to the bulk of the copper to be treated (see also p. 192).

§ 64. Phosphor-copper may be prepared in a variety of ways. (1) By dropping phosphorus upon molten copper in a crucible an alloy rich in phosphorus is obtained, forming an extremely hard, steel-gray, fusible compound. (2) By

reducing phosphate of copper with charcoal, or charcoal and carbonate of soda. (3) By heating a mixture of 4 parts bone-ash, 1 part charcoal, and 2 parts granulated copper at a moderate temperature. The melted phosphide of copper separates on the bottom of the crucible, and is stated to contain 14 per cent of phosphorus. (4) By adding phosphorus to copper-sulphate solution and boiling. The precipitate is dried, melted, and cast into ingots. When of good quality and in proper condition it is quite black. (5) Copperphosphide is easily prepared by adding to a crucible 14 parts sand, 18 parts bone-ash, 4 parts powdered coal, 4 parts sodium carbonate, and 4 parts powdered glass; the whole being intimately mixed with 9 parts granulated copper. A lid is then luted on and the crucible exposed to a strong heat. The sand acts on the bone-ash, forming silicate of lime. The liberated phosphoric acid is reduced by the coal, and the phosphorus thus set free unites with the copper. (6) Montefiori-Levi and Künzel prepare phosphor-copper by putting sticks of phosphorus into crucibles containing molten copper. To avoid a too ready combustion the sticks of phosphorus are previously coated with a firm layer of copper, by placing them in a solution of copper sulphate. (7) By strongly heating in a crucible an intimate mixture of boneash, copper oxide, and charcoal, phosphor-copper is produced.

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§ 65. Phosphor-tin.-(1) When finely divided tin is heated in the vapour of phosphorus, a silvery-white, very brittle phosphide is obtained, containing about 21 per cent of phosphorus. (2) When phosphorus is dropped into molten tin combination takes place with the formation of a white phosphide, containing about 15 per cent of phosphorus. (3) By placing a bar of zinc in an aqueous solution of chloride of tin, a spongy mass of metallic tin is obtained; by placing this moist tin on the top of sticks of phosphorus in a crucible, pressing down tightly, and then exposing to a gentle heat until the flames of burning phosphorus cease, a crystalline mass of phosphor-tin is obtained.

M

The following excellent plan is adopted in some works for the manufacture of phosphor-copper and phosphor-tin.

B

U

Scale of 16

FIG. 27.

A by means

In a cast-iron crucible A, Fig. 27,
is placed the requisite quantity of
phosphorus, then the top crucible
B is tightly joined to
of screw clamps d d. The molten
metal is poured into B and runs
through the opening c on to the
phosphorus. The vaporised phos-
phorus can only escape by passing
through the molten metal, and is
thus almost completely absorbed.

§ 66. Very small quantities of sulphur, arsenic, and antimony render bronze brittle, per cent being sufficient to modify its properties.

The physical properties of bronze depend upon the composition, mode of manufacture, mechanical treatment, and rate of cooling after heating. 1 Riche has examined a series of copper-tin alloys with regard to fusibility, liquation, and changes of density resulting from certain operations. The alloys having the chemical formulæ SnCu, and SnCu are the only ones which melt and solidify without decomposition, and their melting points lie between 600° and 700° C.; all other alloys of tin and copper undergo liquation at the moment of solidification.

The several alloys, in quantities of 500 to 700 grammes, were fused for ten hours in tubular moulds, and the top and bottom portions of the castings were analysed. Another portion of each of the melted alloys was stirred during solidification, and the portion which last remained fluid was poured off and likewise analysed. The following table gives the results:

1 Ann. Chim. Phys. (4) vol. xxx. p. 351.

[blocks in formation]

11. CugSn

79.02 20.98 21.0 21.32
81 15 18.85 18.88 18.56

24.85

Like No. 9.

24.6

Like No. 9.

20.06

Distinctly yellow.

13.1

Gun-metal.

12. Cu10Sn
84-33 15.67 15-18 15-18 24.50
13. Cu1Sn 89.00 11.00

The specific gravity of these alloys is best determined by filing off portions from the upper and lower ends of the casting, and taking the mean of the two densities. In alloys rich in tin expansion takes place (that is to say, the specific gravity of the alloy is less than the mean specific gravities of the two metals) up to the proportion CuSn,; alloys richer in copper exhibit contraction, which is small in the alloy SnCu,, then suddenly becomes very great, attains its maximum in SnCu, and then gradually diminishes, the greatest density,

8.91, is found in the alloy SnCu, even the more cupriferous alloys exhibiting lower densities, e.g. gun-metal, 8·84.

The hardness of the alloys, reckoning from pure tin, increases with the proportion of copper down to CuSn. This and all the more cupriferous alloys down to Cu-Sn are extremely brittle, and from this alloy the hardness diminishes as the proportion of copper increases. The hardness of the alloy consisting of 66.66 parts tin and 33·33 parts copper is said to be the same as that of pure copper.

The alloy SnCu, is distinguished from all the rest by several characters; it presents the same homogeneous composition after repeated fusion, is peculiar in colour, has the highest density, exhibits the greatest degree of contraction, and is so brittle that it may be pounded in a mortar.

Bronzes containing from 18 to 22 per cent of tin, such as are used for making wind-instruments, have their density increased by heating and suddenly plunging into cold water; but on again raising them to a red heat and allowing them to cool slowly the density is lowered, but not to the value it had before the sudden cooling. By mechanical treatment, such as simple compression or the blow of a coining-press, followed by sudden or slow cooling, the density of these alloys is increased, more also (from 8.775 to 8.952) by pressure and sudden cooling than by pressure and slow cooling (from 8·782 to 8.854). These bronzes, therefore, are affected by sudden cooling and by annealing in the opposite manner to steel. They cannot be worked at ordinary temperatures, because they break too easily; they are likewise brittle at a red heat, and between 100° and 200° C. But at temperatures a little below dull redness they may be forged like iron, easily hammered out into thin plates, and reduced from inch to inch thickness by rolling. This property renders them available for the fabrication of gongs, which in external appearance and sonorous qualities, as well as in chemical composition, are identical with the famous Chinese instruments. By the same treatment in the warm state these bronzes are, moreover, rendered denser, and more easily brought to any given density, than by similar treatment when cold.

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