392 Dr. (J. R. Alder Wright. [Jan. 28, 



Fig. 8 represents these values on the triangular system, .the point 

 A indicating an alloy that did not separate, containing Ag = 67'5, 

 Pb = 20-1, Zn = 12-4. 



The position of the limiting point L is found by a large-scale 

 plotting on Stokes' second system to correspond with the values : 



A + A' = 96-4 

 B + B' = 12-6 



whence the composition at the limiting point is : 



Lead = 48"2 

 Zinc = 6'3 

 Silver = 45'5 



100-0 



It is noteworthy that the ratio between lead and ziiic at the limit- 

 ing point thus found with silver as the " solvent " metal, is entirely 

 different from that deduced above when tin is the solvent ; with tin, 

 the ratio corresponds pretty closely with that indicated by the formula 

 PbZn 6 , whereas with silver it corresponds more nearly with Pb 2 Zn. 



Calculated. Found. 



Pb 86-43 48-2 = 88'44 



Zn 13-57 6-3 = 11-56 



100-00 54-5 100-00 



The dotted lines J, II, III at the lower portions oL' the critical 

 curve represent the values described in Series I, II, and III respec- 

 tively (Part II), and indicate very clearly the effect produced by the 

 forma.tion of the definite compound AgZn 5 , and its gradual elimination 

 as previously described. Similarly, the effect of the formation of the 

 compound Ag 4 Zu 5 is readily visible in the right-hand branch of the 

 curve ; the conjugate point Xo. 6 is obviously close to an angle in 

 the curve line and represents an alloy containing silver and zinc in 

 the proportions 54'93 and 41'86, or almost exactly Ag 4 Zn 5 . 



Calculated. Observed. 



Silver 57-07 54/93 = 56' 75 



Lead.. 42-91) 41-86 = 43*25 



100-00 96-79 100-00 



Leaving out of sight the bulge inwards at the lower part of the 

 curve, due to the formation of AgZn 5 , it is noticeable that the critical 

 curve for lead and zinc with silver as "solvent " metal lies outside that 



