purposes, the cause of brittleness has been practically eliminated, so that the alloy can be worked into any desired form. It has been found in practice that certain varieties of German silver become more homogeneous by remelting, and can be worked with greater facility, but this is unnecessary if suitable proportions are selected at the commencement, and copper-nickel alloys with copper-zinc alloys used for melting together to form the desired alloy, instead of using the separate metals. It must also be remembered that each time German silver is remelted in a crucible in the ordinary way, a certain amount of oxide is formed, and a greater portion of the zinc than the copper or nickel is volatilised, so that the relative amounts of the constituents are altered. In the case of remelting it is necessary to add a portion of metallic zinc to compensate for the loss, and it is advisable to add this zinc after the fusion of the alloy has been effected. There is reason to believe that the zinc thus added assists in purifying the metal, by uniting with the absorbed oxygen. Whether this is so or not, the author has proved, that such an addition is beneficial in many cases, if not in all. Great care is required in casting the alloy to avoid chilling of the metal, and as a high temperature is requisite to keep the metal sufficiently liquid for pouring into the moulds, the casting shop is kept closed and all spaces which ordinarily admit cold air are stopped up. All the precautions with regard to blacking and heating of the moulds, etc., as described when speaking of brass strip-casting and moulding, apply also to German silver. But as German silver is more easily chilled than brass, it may be necessary, after one mould is filled, to re-heat the remaining portion of metal in the crucible before pouring it into a second mould. The moulds used for German silver strip-casting are of the same shape as those described for brass-strips, but differ in size. The running sizes of plate-ingots are 16 to 18 inches long, 4, 41, and 5 inches wide, and 1 to 14 inches thick. The V GERMAN SILVER SOLDERS 247 wire-ingots are about 4 feet 6 inches to 5 feet long, 31 inches wide, and 14 inches thick. GERMAN SILVER SOLDERS § 94. Hard solders, employed for joining the parts of German silver articles together, are generally made of the same metals as those which compose the alloy to be soldered, but in such proportions as to have a lower melting point. In general, the soldering is more perfect the nearer the fusing point of the solder approaches that of the metal of which the article is composed, but the greater is the care required to avoid melting it. In some cases silver solder is used for German silver articles; and German silver solder is also used for soldering articles of iron and steel, on account of its high melting point and great tenacity. German silver solder is known by different names, such as "argentan solder," "arguzoid," etc. It is rendered. moderately fusible by the addition of a large proportion of zinc to the copper and nickel. The mode of manufacture is similar to that already described for brass solder, and the proportions of the ingredients will depend upon the composition of the alloy which it is required to solder. For the higher alloys, i.e. those rich in nickel, a more refractory solder is advisable than with the cheaper and more fusible alloys. In making argentan solder the copper and nickel should be melted first, and the zinc added in the free state, or in the form of brass, containing much zinc. The mixture is then cast in thin plates, which are broken into pieces while hot, and crushed to powder in an iron mortar. The facility with which it can be pulverised will depend upon the proportion of zinc. If it is too brittle it indicates too much zinc, and even if somewhat malleable, too much zinc may be present; in either case the defect may be the fresh metal required and remelting. be removed by remelting, when some remedied by adding Excess of zinc may of that metal will burn off, but this is of course wasteful and expensive. The right composition can always be determined by taking a small quantity and testing it before pouring the main portion. lustre. The colour is grayish - white, with a strong In order to test the best proportions for soldering articles containing 16 to 22 per cent of nickel, the author obtained a sample of the solder used by a large manufacturer for the above alloys, which, on analysis, gave the following proportions: The three samples were pulverised whilst hot, and tested by a workman accustomed to use the solder of which the analysis is given above. He considered No. II the best for soldering, but preferred the one he had been accustomed to use. No. III was pronounced porous, from which it was inferred that 57 per cent zinc was too much. CHAPTER VI ALLOYS OF TIN § 95. Tin and Zinc.-Alloys of these metals can be readily produced by fusion, forming combinations that are generally harder and less malleable than tin, softer than zinc, and more or less crystalline in structure. The colour of the fractured surface depends upon the nature of the mould and the temperature of the alloy at the time of casting. The same observations also apply to the shrinkage upon solidification. Tin-zinc alloys are chiefly employed for casting ornamental objects, and patterns. The following investigation into the character of tin-zinc alloys was made by Guettier1 : "1. Tin 30, Zinc 70.-Texture of a dull-white colour; an average shrinkage; breaks easily; on fracture shows larger and brighter facets than zinc; the metal is denser at the bottom of the mould; dry to the file; breaks under the chipping chisel; slightly sonorous; and shows an appearance of crystallisation at the surface, with a slight bluish-yellow colour. "2. Tin 25, Zinc 75.-Texture of a white colour, inclining to blue; slight shrinkage of the bar; bright fracture with large bluish facets like those of zinc; the tin seems to be in larger proportion at the bottom of the button, the same as in No. 1; the surface is covered with a kind of skin, rather 1 Guettier, Guide Pratique des Alliages, 1865. wrinkled than crystalline, and with variegated colours,light blue, violet, and golden yellow. "3. Tin 50, Zinc 50.-Texture, pallid white; surface of the ingot is very smooth, granular, and lamellar, without the appearance of shrinkage; the edges are somewhat round, and do not show plainly the iridescent colours; the fracture is bright and finely granular, upon a tin-white ground; and clogs the file a little; the alloy is well mixed, tough, and malleable, without being soft. "4. Tin 70, Zinc 30.-Texture white; and somewhat shining; exhibits no settling; feebly sonorous; surface granular, and dead white with slightly yellow spots; difficult to break; bears hammering well; easily worked with the chisel, which takes off long chips; it clogs the file; the fracture, like that of tin, is without brightness and crystallisation; when polished it is less bright than tin; the alloy is more complete and uniform in texture than the preceding ones. "5. Tin 75, Zinc 25.-Texture tin-white, but without brightness; exhibits no settling; surface granular and studded with bright particles; the upper surface has a tint changing from yellow to reddish-blue; clogs the file more than No. 4; very malleable, although resisting the hammer and chisel more than No. 4; bends without the crackling sound of tin. "6. Tin 10, Zinc 90.—The bar shows at the fracture the characteristics of a zinc bar; clogs the file more than zinc; the fracture is not of so dull a gray; the bottom of the button is soft and easily receives the impression of a punch; like No. 2, tin appears to settle, and the metal at the bottom is softer than pure tin. "7. Tin 90, Zinc 10.-The bar presents the jagged fracture of tin, and the runner could only be separated by cutting it; the alloy clogs the file less than pure tin; the button settles sensibly in the middle, although the edges are sharp; the alloy is very malleable, although not very soft under the hammer. "8. Tin 1, Zinc 99.-The fracture is like that of zinc, |