390 Dr. C. E. Alder Wright. [Jan. 28, 



of which affects the composition of certain of the heavier alloys, 

 whilst no similar compound appears to be formed between bismuth 

 and tin. Owing to the critical curve for bismuth-zinc-tin being so 

 much lower down than that for lead-zinc-tin, the tendency towards 

 formation of the compound SuZn 4 , which affects the direction of slope 

 of the ties in the latter curve, is almost invisible with the former 

 ones. Some slight indication of an effect is, however, perceptible, the 

 slope of the ties to the right visibly ceasing to increase towards the 

 upper part of the curve in the same marked way as is noticeable at 

 the lower part thereof. It is remarkable in this connexion that the 

 upper ties with alloys of lead and zinc, when tin is the solvent metal, 

 are the only ones sloping downwards to the right, those obtained 

 with lead and zinc when silver, cadmium, or antimony is the solvent 

 metal, uniformly sloping downwards to the left. Precisely the same 

 remarks apply to the corresponding alloys containing aluminium 

 instead of zinc so far as at present examined. 



Alloys of Lead, Silver, and Zinc. 



The experiments detailed in Part II indicate that the position of 

 the limiting point with lead-silver-zinc alloys lies considerably to the 

 left of the central line of the triangle, and not to the right as with 

 the above-described alloys containing tin. Accordingly, a number of 

 additional experiments were made with mixtures containing lead and 

 zinc in proportions from 3:2 to 4 : 1 (according to the amount of 

 silver present), with the object of correcting any possibly erroneous 

 values due to imperfect intermixture owing to inequality between the 

 quantities of heavier and lighter alloys formed ; and also of obtain- 

 ing pairs of conjugate points situated nearer to the limiting point 

 than those already deduced, and thus of enabling the position of the 

 limiting point itself to be calculated. In all these further experiments 

 the percentage of silver in the mixture exceeded 20, so that only those 

 points were re- valued lying nearer to the limiting point than those 

 where the effect of the formation of the compound AgZn 5 in produ- 

 cing irregularity became appreciable. The temperature was 

 750 850 throughout, averaging near to 800 as before. 



The following table represents the average results obtained by 

 taking into consideration these further experiments, together with 

 those described in Series I and II, Part II, none of which were found 

 to be affected by the error due to incomplete intermixture to anything 

 like so great an extent as was found with some few of the ingots pre- 

 pared with tin. The 14 pairs of conjugate points are deduced from 

 the examination of 39 compound ingots in all, representing 78 ternary 

 alloys. Each point, therefore, nearly represents the average of three 

 alloy analyses. 



