2f.fi Mr. K. Matth.-y. [Mar. 15, 



series of the alloys of the precious metals and metals of the platinum 

 group, and the results have been published in the ' Philosophical 

 Transactions ' for 1892, and in other papers to which reference may 

 be made.* It is, however, in the case of alloys of silver and copper 

 that liquation is most marked, and gives rise to results of much inte- 

 rest and industrial importance. It is, for instance, often a matter of 

 great importance to obtain a plate of standard silver (925 parts of silver 

 in 1000) of uniform standard. The great difficulty of effecting this has 

 been shown by Roberts-Austenf, and, as the results of an elaborate 

 series of experiments, he was led to the conclusion that slow and uni- 

 form cooling of the mass was most effective in obtaining uniformity 

 of standard. He informs me of a fact of which I was not aware until 

 the present experiments were concluded, viz., that be also tried the 

 effect of the rapid cooling of a thin casting in a large mould which 

 was no less than 45*7 cm. long. He found, however, that castings 

 made in this mould were comparative failures as regards uniformity 

 of standard, and that, as in the case of other published results given 

 by castings in thicker moulds, it was not possible, either by rapid or 

 by slow cooling, to obtain masses of alloys which did not give points 

 of local richness. 



During the last few years I have returned to the investigation of 

 the silver-copper alloys, and as the results of a series of some hun- 

 dreds of experiments, only the final ones of which must be referred to 

 here, I find that it is preferable to cast the alloy very thin, and to 

 promote the uniformity of cooling. 



A bar of this alloy was cast into a " skillet" mould to produce a 

 casting 30 cm. in length, 13 cm. in width, and 6 mm. in thickness, 

 weighing 5 kilos. Pnnchings were taken through its thickness at 

 the points marked, and the assays which were made of these punch- 

 ings showed the composition at the respective points to be as 

 follows : 



'Phil. Trans.,' 1892, A, pp. 629-652, and 'Roj. Soc. Proc.,' TO!. 47, 18 

 pp. 180186. 



t ' Roy. Soc. Proc.,' rol. 23, 1875, p. 481, and ' Chero. Soc. Journ.,' vol. 27, 1874, 

 p. 197. 



