106 sir W. Etoberte-Auaten and Dr. T. Kirk.- Rose. 



copper alloy containing 0'2 per cent, of impurity a certain amount of 

 the gold was driven to the inside of the mass by solidification. Cor- 

 roborative evidence was subsequently obtained by the aid of the cool- 

 ing curves afforded by the recording pyrometer, a description of which 

 has already been submitted to this Society. 



To decide the point finally it was desirable to show to what group of 

 alloys the gold-copper series belongs, and in particular to determine 

 whether the freezing points of the various alloys would lie on a single 

 continuous curve connecting the freezing point of gold with that of 

 copper. 



Freezing-point curves were accordingly taken by the recording 

 pyrometer of a comprehensive series of alloys. In each case 100 

 grammes of the alloy were employed, and the thermo-couple, protected 

 by a very thin clay tube, was inserted in the molten mass, which had 

 been previously thoroughly stirred. The rate of cooling was pro- 

 longed as much as possible by allowing the crucible and its contents 

 to remain in position in the gas furnace in which the melting had 

 been effected. The freezing points of this series have, so far as we 

 are aware, never been published, except a few at the copper end 

 by Heycock and Neville.* MM. Charpy and Riche have, however, 

 recently stated that the curve of fusibility of the alloys of gold and 

 copper consists of two branches meeting at a point corresponding to 

 the eutectic alloy which, according to these experimenters, contains 

 55 per cent, of gold, alloyed with 45 per cent, of copper, and fuses at 

 940. t This conclusion is not confirmed by the results of our experi- 

 ments, which are given in the accompanying table and are plotted in 

 the curve, fig. 1. 



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



f ' Administration des Monnaies et J Medaillcs. Rapport au Mini? tre des 

 Finances,' 1899, p. xixviii. 



