.892.] 



On certain Ternary Alloys. 



17 



This coincidence would seem to suggest that the peculiar disposi- 

 tion of tie-lines with these two series of alloys (not observed with 

 any others) is due to the tendency towards the formation of the 

 definite compound, SnPb 3 ; on the other hand, in neither case is any 

 bulge inwards or outwards noticeable in the contour of the critical 

 curve at the part corresponding with this compound, such as 

 observed in the case of the atomic compounds AgZn 5 and Ag 4 Zn 5 . 



JS 





Fig. 1 represents the critical curve plotted from the figures con- 

 tained in the above table ; obviously it lies outside the analogous 

 curves obtained at 650 and 800 with zinc-lead-tin alloys (Part V, 

 figs. 4 and 5). The former of these is shown by the inner dotted 

 line. The slopes of the upper ties suggest that there is some 

 tendency towards convergence to a point on the right-hand side ; the 

 central point of that part of the curve where this tendency is mani- 

 fest (marked P in the figure) is that representing the composition 

 tin = 49, lead = 6, aluminium = 45, which is close to that represented 

 by the formula SnAl 4 , so far as the ratio between tin and aluminium 

 is concerned. 



VOL. LII. c 



