82 PHYSICAL SCIENCE 



a liquid of one composition, say c, is in equilibrium 

 with a solid of another composition, such as d. 

 As the process of solidification proceeds, the 

 composition of both liquid and solid changes 

 continuously. In the light of these theoretical 

 curves, the complicated experimental curves, found 

 by observing the freezing-points of mixtures of 

 metals and of other substances, are now being 

 interpreted in a manner which otherwise would 

 have been quite impossible. 



One of the most successful examples of such an 

 interpretation is given by the very thorough study 

 which was made by Heycock and Neville of the 

 bronzes, that is, of alloys consisting of copper 

 and tin. The curves in Fig. lo show the results 

 of their own experiments and of previous work by 

 Roberts- Austen. Heycock and Neville examined 

 microscopically the structure of various alloys of 

 the two metals in conjunction with the equilibrium 

 curves, and gave us a knowledge of the bronzes 

 more complete than that which we then possessed 

 for any other series of alloys showing phenomena 

 of an equal degree of complexity. 



Fig. lo shows the equilibrium curves, from 

 pure copper on the left to an alloy containing 80 

 atomic percentages of tin on the right. Above 

 the "liquidus" abcdefgh the alloys consist of a 

 homogeneous liquid, in which solid first begins 

 to form when the temperature falls to points 

 represented on the curve. The "solidus" curve, 

 below which the whole mass is solid, is the 

 complicated curve hblcmef'£.^Y.^^!'u. 



It has long been known that the physical 

 properties of metals, especially of alloys, depend 

 on the way in which they are cooled from a state 



