386 Dr. C. R. Alder Wright. [Jan. 28, 



the curves marked 1 are closely in accordance with those deducible 

 by shifting the curves marked 2 upwards on the paper ; so that it 

 may fairly be inferred that whilst the values of A + A' and B + B' at 

 the limiting point are close to 45 and 85 respectively, those for curves 

 No. 2 are not far from A-f A' = 48, and B + B' = 88, as indicated by 

 the dotted prolongations : whence, the compositions at this limiting 

 point for 650 C. and 800 C. respectively are close to 



At 650. At 800. 



Lead 22-5 24'0 



Zinc 42-5 44-0 



Tin. . 35-0 32-0 



100-0 100-0 



The points marked LI and L 2 (fig. 5) respectively indicate these com- 

 positions. 



It is worthy of notice that in each case the ratio between lead and 

 zinc is not far from that indicated by the formula PbZn 6 . 



Found. 



Calculated. At 650. At 800! 



Lead.. 34-67 22-5 = 34-62 24-0 = 35-29 



Zinc., 65-33 42*5 = 65'38 44*0 = 64'71 



100-00 65-0 100-00 68-0 lOO'OO 



A priori, it would seem not impossible that the position of the 

 limiting point might correspond with the formation of a definite 

 compound of the two immiscible metals, soluble in the " solvent " 

 metal to an extent varying with the temperature. On the other 

 hand, the experiments subsequently described show that when silver 

 replaces tin as solvent metal an entirely different ratio between lead 

 and zinc subsists at the limiting point thus found, more nearly ap- 

 proximating to Pb 2 Zn. Experiments now in progress, moreover, 

 indicate that with antimony as solvent metal a third ratio, approxi- 

 mately PbZttj, is deduced. 



It is further noticeable that the upper tie-lines, depicted in fig. 4 

 (Nos. 9 to 14), visibly converge together in such fashion that the 

 point representing the composition Sn = 28, Pb = 11, Zn = 61 per 

 cent, lies in the midst of them all. This configuration obviously 

 suggests that there is a tendency to the formation of some definite 

 compound, such that whilst a considerable range in composition is 

 shown by the heavier alloys, a much smaller one is observed in the 

 case of the lighter alloys conjugate therewith ; that this compound is 

 indicated by the formula SnZn* is strongly suggested by the circum- 



