

218 Dr. T. Kirke Kose. On certain [Feb. 9, 





" On certain Properties of the Alloys of Silver and Cadmium.' 

 By T. KIRKE ROSE, D.Sc. Communicated by C. T. HEYCOCK, 

 F.RS. Received February 9, Read February 11, 1904. 

 [PLATE 10.] 



It has long been known that an alloy of silver and copper is not a 

 satisfactory material for the trial plates which are used in testing the 

 fineness of the Imperial silver coin and of silver wares before they are 

 hall-marked. As long ago as the year 1580 the lack of homogeneity 

 of silver-copper alloys was well known to the German metallurgists,* 

 and in 1852 Levol concluded! that the only uniform alloy of the 

 series contained 718'93 parts of silver and 281-07 parts of copper, 

 a composition which corresponds to the formula Ag 3 Cu 2 . In 1875 

 Roberts-Austen, as the result of very carefully conducted experi- 

 ments,! found that under the most favourable circumstances the 

 difference in composition between the centre and corners of a small 

 ingot amounted to 1-2 parts per 1000, and was generally much 

 greater. In 1899 when further attempts were made to prepare ingots 

 of silver and copper of uniform composition, similar results wei 

 obtained, although many castings were made in accordance with th( 

 method recommended by E. Matthey.j) 



A consideration of the cooling curve of the standard silver-coppei 

 alloy, containing silver 92 '5, copper 7 '5 by weight, which was obtaim 

 by Roberts- Austen,H and is reproduced in C fig. 1, shows that sucl 

 segregation must necessarily take place. The initial freezing point 

 of this alloy, in which the percentage by atoms is silver 87 '9, cop] 

 12*1, is at about 900. At this temperature a solid solution rich in 

 silver begins to crystallise out, but solidification is not complete until 

 the temperature has fallen to 778 (d% fig. 1), when the mother liquor 

 contains only 60 atoms of silver to 40 of copper, that is to say, th< 

 proportion found by Heycock and Neville to be present in the eutectic 

 alloy.** During the pasty stage ample time is allowed for th< 

 segregation of the silver-rich constituent, with the result that th( 

 distribution of silver in the solidified metal is not uniform. Tl 

 amount of segregation varies with the dimensions of the ingot 



* See pp. 20 and 26 of ' Allerfurnemisten Mineralischen Eerzt und Bergwei 

 arten,' by L. Ercker. Published at Frankfoit in 1580. 



t 'Ann. de Chimie et de Phys.' (3), vol. 36 (1852), p. 193 and vol. 39 (1853) 

 p. 163. 



J 'Koy. Soc. Proc.,' vol. 23 (1875), p. 481. 



Thirtieth Annual Report of the Mint (1899), p. 69. 



|| ' Roy. Soc. Proc.,' vol. 55 (1894), p. 265. 



f First Report to the Alloys Research Committee, 'Inst. Mecli. Eng. 

 1891, p. 543. 

 ** 'Phil. Trans.,' A, vol. 189 (1897), p. 25. 



