1892.] On the Liquation of Metals of the Platinum Group. 447 



III. " On the Liquation of Metals of the Platinum Group." By 

 Edward Matthey, F.C.S., F.S.A., Ass. Roy. Sch. Mines. 

 Communicated by Sir G. G. Stokes, Bart., F.R.S. Received 

 March 3, 1892. 



(Abstract.) 



The author has continued a previous investigation of his own 

 which was published in the ' Proceedings of the Royal Society ' 

 ('Roy. Soc. Proc.,' 1890, vol. 47, pp. 180—186). 



In the present paper he discusses, in much detail, the effects of the 

 cooling of large masses of the alloys gold-platinum, gold-palladium, 

 platinum-palladium, platinum-rhodium, and gold-aluminium. 



The details of manipulation, which were of considerable difficulty, 

 are set forth in detail, as they involved melting masses of metal with 

 high melting points. 



The author regrets that time has not enabled him to examine more 

 members of each particular series of alloys, so as to present results 

 in fuller detail : in fact, the silver-copper series is the only one upon 

 which anything like exhaustive work has been done. 



No doubt, in every series of alloys there is one definite alloy which 

 would yield a uniform mass on cooling, and it is known that in the 

 silver-copper series this alloy (Levol's) contains 718 parts of silver 

 per thousand. It is not certain, however, that this is the eutectic 

 alloy of the series — that is, the one with the lowest melting point — 

 but it is well known that when silver-copper alloys which contain 

 more silver than 718 parts per thousand are cooled, the centre of the 

 solidified mass is richer than the exterior. This is the case with 

 standard silver, for instance, which contains 925 parts of silver per 

 thousand, and it is safe to conclude that an alloy rich in copper is the 

 first to fall out from the mass, and that this alloy sets round the 

 inner surface of the mould, driving a still fluid alloy, rich in silver, 

 to the centre. The general rule in the present results seems to be 

 that, in the cooling of a fluid mass of two united metals an alloy rich in 

 the more fusible constituents of the mass falls out first, driving the less 

 fusible constituent to the centre. The gold-platinum alloys (A, B, 0, D, 

 and E) seem to be always rich in gold externally. 



It is remarkable that the metals of the platinum group do not 

 show much liquation among themselves, but, on the other hand, when 

 gold is united to members of the platinum group, there is evidence 

 of liquation. 



The gold-palladium one (F) follows the above rule. 



There is evidence that the alloy E, containing 750 parts of platinum 

 and 250 of gold, is near the composition of a true compound, as it 

 shows but little sign of liquation, and is, moreover, hard and brittle, 



