Ill' I'n.f. .!. A. Kwiug. 



and poorest parts of the plate is usually from I'D to 3*0 parts per 

 thousand, or three or four times as great as that in the case of 

 standard gold. The poorest part in the gold plate is, however, always 

 in the centre and the richest part at the outside. 



The assays made on the " get " of the gold plates, the place on the 

 top of the casting where shrinkage of the mass on solidifying is marked 

 externally by a depression, showed that this part was usually richer in 

 gold than any other part of the plate. These assays are not included 

 in the means given above. 



Conclusion. 



It will be evident from the results given above, that when a small 

 proportion of copper is added to gold, the alloy sets as a whole, and 

 forms a solid solution. If small amounts of copper are successively 

 added, the limit of solubility of that metal in gold is at length reached, 

 and a eutectic separates, which forms the whole mass when about 82 

 per cent, of gold and 18 per cent, of copper are present. 



Comparatively small additions of gold to copper saturate the latter, 

 and the eutectic makes its appearance before the proportion of gold 

 reaches 27 per cent. The composition of the eutectic corresponds 

 approximately to 60 atoms of gold and 40 of copper, while the silver- 

 copper eutectic also contains nearly 60 atoms of silver and 40 of 

 copper. In other respects also, in the brittleness of the eutectic, in 

 the limited mutual solubility of the two metals, and in the liquation 

 which attends solidification, the gold-copper and silver-copper series 

 resemble each other closely. The main difference is that copper 

 appears to be more soluble in gold than in silver, so that the charac- 

 teristics of the gold-copper alloys are less marked, and consequently 

 have been less easy to detect. 



" The Crystalline Structure of Metals." Second Paper. By J. 

 A. EWIXG, F.R.S., Professor of Mechanism and Applied 

 Mechanics in the University of Cambridge, and WALTER 

 ROSENHAIN, B.A., St. John's College, Cambridge, 1851 Exhi- 

 bition Research Scholar, Melbourne University. Received 

 May 17, Read May 31, 1900. 



(Abstract.) 



The investigations described in this paper deal principally with the 

 phenomena of annealing. The first section of the paper describes 

 experiments made in the hope of observing under the microscope the 

 process of recrystallisation in strained iron. It is well known that 



