RECENT PROGRESS IN THE STUDY OF ALLOYS. 91 



called a saturated solution of one metal in the other. The 

 proportions in which the two metals were mixed will 

 determine the relative quantities of the two resulting 

 liquids, but will not affect their percentage composition. 

 When the temperature falls the two conjugates will alter in 

 composition, and when solids begin to separate we may 

 expect to find considerable complexity in the resulting body 

 without the necessity of assuming chemical combination to 

 have taken place. Let us consider the case of the metal A, 

 having a high melting point and present in such excess that 

 the second metal B, with a lower melting point, is com- 

 pletely soluble in it. Moreover, let the mixture be above 

 the temperature L at which A melts. If we now slowly 

 cool this homogeneous system one of two things will happen, 

 it may separate into conjugates or it may remain homo- 

 geneous until pure A begins to separate out in the solid 

 form at a temperature M below the freezing point L of the 

 pure substance A. 



We will consider the latter case. If a thermometer be 

 immersed in the mixture, it will indicate a short period of 

 stationary temperature as soon as A begins to crystallise 

 out ; this is the first freezing point. As A continues to 

 separate the solution of B in A becomes stronger, and, in 

 virtue of the Raoult law, A will crystallise out at a con- 

 tinually lower and lower temperature. But a moment must 

 come when, on account of the removal of A in the solid 

 form, the remaining liquid becomes saturated with B. The 

 conjugate of this liquid will now begin to form, and as A 

 continues to freeze out, more and more of this new liquid 

 will be produced at the expense of the first ; but during this 

 stage neither liquid will alter in composition, and therefore 

 we should expect A to continue separating at a constant 

 temperature N. As soon as the new saturated solution of 

 A in B is the only liquid left, the temperature will begin to 

 fall with continued separation of A or perhaps of solid 

 conjugates of the remaining liquid. This fall in tempera- 

 ture will continue until the liquid is saturated both with A 

 and B, that is until we have reached the eutectic solution 

 of A in B at the temperature P. From this point A and 



