RECENT PROGRESS IN THE STUDY OF ALLOYS. 85 



prevent separation, the ingot was seen to consist of two 

 layers having a well-marked dividing surface between 

 them. 



His results admit of being very elegantly expressed by 

 a method suggested by Sir George Stokes. Suppose that 

 a mixture be made containing a per cent, of A, b per cent, 

 of B, and c per cent, of C ; then, if we draw an equilateral 

 triangle A B C and find the centre of gravity P of masses 

 a, b, c, placed at the corners ABC respectively, the point 

 P will record the composition of the mixture. Conversely, 

 every point in the area of the triangle represents a different 

 mixture. For example, the point P in figure 2 represents 

 a mixture of two parts of A, one of B, and one of C. 



Now, Alder Wright's results show that if the percentage 



Cadmium 



Bcs-mu.th ZiTtC 



of the third metal C, which mixes freely with both A and B, 

 and may therefore appropriately be called the solvent, be 

 small enough, that is, if P be near enough to the line A B, 

 and not too near either A or B, then the alloy represented 

 by P separates into two conjugates represented by the points 

 R and S lying on a straight line through P. If a series of 

 mixtures of A, B, and C in different proportions be examined, 

 and the conjugates into which they divide be found by ana- 

 lysis of the upper and lower parts of the ingots, we can plot 

 a series of points, such as R S. The curve passing through 

 all these is called the critical curve. Figure 2 gives Alder 

 Wright's critical curve for mixtures of bismuth, zinc, and 

 cadmium at 6oo° C. 



