X SILVER ALLOYS 321 alloys. Those with excess of zinc are granular, but with an excess of silver the fracture becomes columnar. The metals combine much more readily at a high than at a moderate temperature. 1 Berthier prepared an alloy containing 80 per cent silver, which he states was rolled into very thin leaf; it was rigid, elastic, very tenacious, and tough. 2 Mr. G. H. Godfrey prepared the following alloys by pouring molten zinc into molten silver : "I. The surface was bluish-gray. The metal was hard, easily frangible, and easily scratched with a knife. Its fracture was bluish-gray, finely granular, and feebly lustrous. "II. The surface was bluish-gray. The metal was harder than No. I, easily frangible, but less easily scratched. Its fracture was bluish-gray, bright, and fibro-columnar. "III. The surface was copper-red after solidification. The metal was hard, brittle, and easily pulverised. The broken surface, when fractured cold, was white and very bright, and somewhat columnar. 66 'IV. The surface had a faint reddish-yellow tint. The metal was hard and easily frangible; its fracture white and very bright, but it soon tarnished; it was columnar in structure." An alloy of 2 parts by weight of zinc and 1 part silver is said to be ductile, finely granular, and nearly as white as silver.3 Silver-zinc alloys have been proposed for coinage purposes. Peligot prepared alloys containing 5, 10, and 20 per cent of zinc respectively. They were white, with a tinge of yellow. The coins were elastic and sonorous. These alloys are not so readily blackened by sulphuretted hydrogen as silvercopper alloys. 1 Traité des Ess. (2) p. 798. 2 Percy's Gold and Silver, vol. i. p. 169. Y § 154. Silver and Iron. These metals do not alloy well together. Messrs. Stoddard and Faraday made some experiments with silver in steel, and concluded that of silver corresponds to the best mixture. These alloys do not appear to present any practical interest. § 155. Silver and Nickel.-Berthier described an alloy of these metals containing 13.5 per cent nickel which was white, and capable of a high polish; it rolled well, and was very tough. There appears to be very little known concerning alloys of these two metals alone. § 156. Silver and Lead.-Alloys of these metals are of little interest from a coinmercial point of view. The metals readily unite in all proportions. A very small amount of lead is sufficient to diminish the malleability and ductility of silver. Molten lead dissolves silver just as mercury does, and homogeneous mixtures are obtained only while the metals are liquid, a certain amount of liquation taking place as the metals cool. 1 Levol has investigated this subject, and his results are tabulated below. 1 Mémoire sur les Alliages, Ann. de Chim. 1853, 3, ser. 39, p. X SILVER ALLOYS 323 I. Grayish-white, but little malleable, and contracts during solidification. II. Grayish-white, resembles platinum in colour and grain, contracts during solidification, and changes rapidly in moist air. III. Grayish-white; contracts strongly during solidification; heated in air it assumes a beautiful violet-blue tint. IV. Alloy tolerably malleable, but has only feeble tenacity, and melts near cherry-red heat; it is bluish-gray in colour, and quickly oxidises in moist air. V. 1 Is much more like lead than silver, soft, and tolerably malleable and ductile. The others require no special comments. § 157. Silver and Aluminium.-Alloys of these metals were made some years ago, and it was thought that valuable metals of a white colour, and unaffected by the atmosphere, would be obtained, which would make them superior to ordinary silver-copper alloys, but these great expectations have not as yet been realised. Aluminium hardens silver, and the alloys admit of a high polish. 2 MM. C. and A. Tissier state that an alloy of 4.75 per cent silver and 95.25 aluminium is more elastic and harder than aluminium, and as malleable as the latter metal. Aluminium alloyed with 10 per cent silver is no longer malleable. An alloy of equal parts of silver and aluminium is said to be as hard as bronze. 3 Lange uses an alloy of 100 parts aluminium and 5 parts silver for watch-springs. Such springs are said to be very elastic, hard, light, not so brittle as steel, and not to rust. Tiers-argent (one-third silver).—This alloy is said to be manufactured at Paris into various utensils, and consists of 33.33 parts silver and 66.66 parts aluminium. MM. Tissier state that this same alloy may be used as a 1 Guettier, Guide Pratique des Alliages, 1865, p. 150. solder, but it runs with difficulty and produces a brittle joint. § 158. Silver and Copper. These metals unite in all proportions, forming a series of most valuable alloys, having a great variety of applications in the Arts. Combination takes place with expansion, so that the specific gravities are less than the mean of their constituents. Most of the alloys are as ductile as silver, and possess more hardness, elasticity, and sonorousness. The colour of these alloys is white until the copper reaches nearly 50 per cent, and beyond that the colour is yellowish, up to about 70 per cent copper, when a red tint prevails. The hardest alloy is that containing 5 parts by weight of silver to 10 or 11 parts copper. 1 Professor Roberts-Austen has determined the melting points of certain silver-copper alloys, and states that the alloy containing 630-29 of silver per 1000 of alloy, and represented by the formula AgCu, has a lower melting point than silver, or than any other alloy of silver and copper. His results are given in the following table. He has since communicated to the author the fact that the results are too high, as more recent determinations of the melting point of silver make it 940° C. instead of 1040° C. According to J. Violle its melting point is 954° C.2 1 Pro. Roy. Soc. vol. xxiii. pp. 349, 481. 2 Compt. rend. tom. lxxxv. p. 543. ཟ The alloys numbered 7 and 8 are of especial interest. The first AgCu2 is Levol's homogeneous alloy, which remains uniform in composition, while many others undergo liquation on slow cooling. The alloy AgCu has the simplest atomic relation and the lowest melting point. In studying the phenomena of liquation, the alloys were cast in moulds of fire-brick, in which the metal (about 50 ounces) could be quickly or slowly and uniformly cooled. The results showed that the homogeneity of Levol's alloy is slightly disturbed by this method of casting; and, on the other hand, that alloys which contain more than 71.89 per cent of silver hardly show signs of rearrangement when the solidification takes place gradually. Two alloys containing 63 and 33.3 per cent of silver respectively, were found to be far from homogeneous, and in the former the arrangement was influenced by gravity, the base of the casting being richer in silver. The following table contains a summary of Roberts-Austen's results : |