412 Mr, C. T. Eeycoch on Metallic Alloys, &c. [April 2, 



of aluminium to protect them from the air. These sections were then 

 placed on a photographic plate, enclosed in a light-tight bag, and 

 exposed to the action of the X-rays. On developing the plate we 

 found a complete picture of the inside of the alloy. Positives 

 obtained from these negatives are thrown upon the screen. The 

 sodium is seen to have crystallised out in plates, as is evident from 

 its transparency, whilst the opaque gold is seen to have become 

 concentrated in the mother liquor between these plates, where it 

 finally solidified along with some of the sodium. 



Very similar results are produced with other pairs of metals, 

 such as aluminium and gold and aluminium and copper. Behrens, 

 Eoberts-Austen, Osmond and others have examined alloys, after 

 superficial etching, with high microscopic powers, and they find a 

 similar separation of the constituents. 



We thus see that solution of metals in one another follows 

 extremely closely the same laws that regulate solutions with which 

 we are ordinarily familiar. I should like to state here that the 

 matter of this lecture is largely drawn from the work carried out by 

 Mr. Neville, F.R.S. and myself during the past six years. 



[C. T. H.] 



