FUSION AND SOLIDIFICATION 



83 



of fusion. The whole process of the annealing or 

 tempering of steel depends on a perception of this 

 fact. Many observers had studied the changes of 

 physical properties thus produced by examining 

 microscopically the solid alloys obtained by 

 different treatments, and relations between the 

 properties of the alloy and its microscopic structure 



Percentage ty Wei^t of Tin 



A' 



oc 



300 ■ 



a + 8 



Fig. 10. 



had been traced. But for the first time a com- 

 plete investigation was made by Heycock and 

 Neville of the changes in microscopic structure 

 produced by different methods of cooling, and 

 studied in conjunction with the equilibrium curves 

 by the light of the theory of solid solutions. The 

 work was rendered possible by the fact that, if a 

 hot metal be cooled suddenly from any tempera- 

 ture by chilling it in cold water, the microscopic 



