222 Messrs Hey cock and Neville, [Nov. 23, 



Monday, 23 November, 1896. 

 Mr F. Darwin, President, in the Chair. 



The following were elected Fellows of the Society : 



H. M. Macdonald, M.A., Fellow of Clare College. 

 G. H. J. Hurst, M.A., Fellow of King's College. 



The following Communications were made to the Society : — 



(1) On the Superficial Colour of a Silver-Zinc Alloy. By 

 C. T. Heycock, M.A.,' King's College, and F. H. Neville, M.A., 

 Sidney Sussex College. 



Whilst granulating by pouring into water an alloy of silver 

 and zinc whose composition was very nearly AgZn (62'25 °/ Ag) 

 we found that it was superficially coloured a red tint closely re- 

 sembling that of copper although before melting it was silvery 

 white. The only reference we can find in the text books is in 

 Percy's Metallurgy where it is stated that some alloys of silver 

 and zinc acquire a pale pink tinge on exposure to air. A variation 

 in the composition of the alloy to the extent of 5 per cent, of 

 silver more or less does not much impair the colour, but with a 

 deviation from AgZn of 10 per cent, of silver the effect is no 

 longer noticed. 



The present communication contains the results of some ex- 

 periments we have made on this coloration. There appear to be 

 two methods probably not radically different of turning the silver 

 white alloy into the red state. The best way is to heat the alio} 7 

 up to a temperature near 300° C, 285° is the lowest effective 

 temperature, and suddenly to chill it. In this way it acquires a 

 fine red colour, provided that the cooling has been rapid. The 

 necessity for rapid cooling is connected with the fact that if the 

 red alloy is heated to 150° C. it turns white. It thus appears 

 that the red colour is due to a substance which cannot exist above 

 150°, and which cannot come into existence unless the body be 

 heated to 300° C. 



These peculiar conditions distinguish the phenomenon from all 

 superficial colour changes of metals known to us. 



We found that the cooling could be effected by letting filings 

 of the alloy fall through the air or by throwing the hot metal into 

 water, alcohol, benzene or ragosine. As the last two liquids con- 

 tain no oxygen it became doubtful whether the presence of oxygen 

 was indispensable for the effect. We made numerous experiments 

 to settle this point, the most conclusive being the formation of 



