ON THE CHEMICAL COMPOUNDS CONTAINED IN ALLOYS. 



143 



Atomic Percentage. 



other, but to a limited extent, the curve will show a depression as we 

 leave pure A, a flat for alloys containing two conjugate solid phases each 

 a saturated solution of one 



metal in the other, and a Fig. 11. 



further depression as we ap- 

 proach pure B. If, however, 

 compounds of A and B exist, 

 that one nearest in composi- 

 tion to A will be indicated by 

 a marked fall in the potential 

 as we reach its formula in 

 going from A to B along the 

 curve. He gives experimental 

 curves showing that this is 

 the case with the 

 pairs : — 



following 



ZnCu at Zn,Cu. 

 ZnAg at Zn4Ag. 

 ZnSb at ZnSb,. 

 SnCu at SnCug. 

 SnAg at SnAg4. 



The curves, four of which 

 are reproduced in this report 

 (fig. 11), show that the phe- 

 nomena are well marked. 

 The numbers in the figures 

 running from left to right 

 are atomic percentages of the 

 metal whose symbol is on the Z 

 right of the figure. 



If we compare Hersch- 

 kowitz's SnCu curve with 

 our freezing-point curve for 

 the same metallic pair in 

 which the indication of the 

 existence of SnCu^ is of the 

 slightest kind, we see how 

 very useful the method may 

 be in detecting compounds. 

 It appears, however, that 

 only one compound of each 

 metal pair is likely to be 

 indicated by the method. It 

 is probable that the method, 

 if it can be carried out accu- 

 rately, will give us valuable 

 indications as to the solubility 

 of one metal in the other in the solid state — a point on which both the 

 microscope and the freezing-point curve are ambiguous. Although Laurie 

 was the originator of this method, the work of Herschkowitz has been 

 quoted, as it is more recent and founded on a clearer theory. 



0% ID 



