36 



Dr. Alder Wright and Mr. C. Thompson. [May 8, 



by amounts outside the limits of variation ascribable to unavoidable 

 differences of average temperature and fluctuations of temperature in 

 the several experiments, both rising slowly until a point is reached 

 when a very marked change takes place in the rate of ascent. 



It : is especially noticeable that the position of the first maximum is 

 in each case close to that when the ratio between silver and zinc in 

 the alloy is indicated by the formula AgZn 5 



Further, the points where the rate of ascent suddenly becomes 

 much more rapid are in neither case far from that indicated by the 

 formula Ag 4 Zn 5 



As regards these points, it is remarkable that alloys where upwards 

 of nine-tenths of the whole consists of silver and zinc in the propor- 

 tion Ag 4 Zn 5 exhibit a distinct coppery red hue when a recently filed 

 or polished surface is exposed to the air for a short time. As the 

 proportion of Ag 4 Zn 5 present diminishes owing to the presence of 

 excess of silver, or of zinc, or of either with additional lead, the red 

 colour becomes less marked, the tint being only a pale yellow, or even 

 entirely white, when the alloys contain less silver and more zinc, or 

 more silver and less zinc, than about the limits 



Silver 42 per cent. 



Lead 3 ,, 



Zinc 55 ,, 



100 



62 per cent. 

 10 



_28 



100 



