Page:Proceedings of the Royal Society of London Vol 60.djvu/39

Rh the extra richness of the gold over 77*5 being due to the volatilisation 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 s' 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 Lead Zinc 75-0 15-0 10-0

Cooling curve o f Au,Cu,Zn,Pb. a 73/ °C. 6 635° C.(main p o in t) C 407° C. d 247° C. e 206° C. Time.


 * See ‘ Roy. Soc. Proc./ vol. 52, p. 467.