On the Liquation of certain A Hoys of Gold. 



31 



the extra richness of the gold over 77'5 being due to the volatilisa- 

 tion of the zinc. This experiment appears to confirm, that on pp. 27, 

 28 (see results of fig. 4). 



The foregoing experiments show that lead is far more effective as a 

 cause of liquation than zinc, and the question arises, do zinc and lead 

 separate into distinct layers by gravity when they are simultaneously 

 present in a mass of gold, as they are known to do when they (lead 

 and zinc) are melted together and allowed to solidify slowly. If they 

 do separate, are they respectively associated with precious metal ? 

 Professor Roberts-Austen has given us a method of investigating 

 such a problem. He has shown that it is easy to place a suitably 

 protected thermo- junction in a mass of cooling alloy, and obtain by 

 photography a record of the cooling of the mass,* a method which 

 was employed by me for determining the temperatures at which the 

 metals arsenic and antimony separate from bismuth. Applying 

 this method to a mass weighing 44 grams of an alloy containing : 



Gold , . . . 75-0 



Lead 15-0 



Zinc lO'O 



The following curve, No. I, is an autographic record of its solidifi- 

 cation : 



CTTEVE No. I. 



Cooling curve of Au,Ca,Zn,Pb. 



73, C. 



655 C. ("main point) 



407 C. 



*rC. 



206 C. 



Time . 



* See ' Boy. Soc. Proc./ vol. 52, p. 467. 



