180 



Mr. E. Matthey. 



[Feb. 13, 



February 13, 1890. 



Sir Gr. GABRIEL STOKES, Bart., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : — 



I. "The Liquation of ' Gold and Platinum Alloys." By 

 Edwaed Matthey, F.S.A., F.C.S., Associate Royal School 

 of Mines. Communicated by the President. Received 

 January 17, 1890. 



It is a well known fact that when molten alloys of certain metals 

 are cooled, some of the constituents separate and become concentrated 

 either in the centre or in the external portions of the solidified mass ; 

 to this segregation the name of liquation is given. It is specially 

 noticeable in the case of silver-copper alloys, and its importance is 

 now being widely recognised in almost all branches of metallurgy. 



In the case of gold, however,, the phenomenon of liquation does not 

 appear to have been much observed. Gold alloys, to the value of 

 many millions sterling, pass annually from hand to hand upon the 

 results of assays cut from the external portions of ingots, which 

 assays cannot, of course, be trustworthy, if the centre of the bars 

 differs in composition from the external portions. Peligot has 

 recently endeavoured to obtain evidence of liquation in gold-copper 

 alloys, and has concluded that it does not exist.* Roberts-Austen, f 

 who has devoted much time to the study of liquation, has also 

 satisfied himself that gold-silver alloys do not rearrange themselves 

 on cooling. J 



It is, of course, well known that gold does not retain on solidify- 

 ing certain metals of the platinum group ; for instance, iridium, 

 when associated with it, always tends to fall through the fluid metal, 

 and is found at the bottom of the solidified mass, but this is probably 

 not a case of true rejection of a metal by liquation, but is due to the 

 higher specific gravity of the iridium, coupled with the fact that the 

 usual heat at which gold is melted is not sufficiently high to bring 



* ' Bulletin Societe d'Encouragement,' 1889, p, 481. 



\ ' Boy. Soc. Proc.,' toI. 23, 1874, p. 481. 



X ' Nineteenth Annual Keport of the Mint,' 1888, p. 35. 



