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XX. Experimental Exammation of Platina. 
By William Lewis, M. B. F. R. S. 
' PAPER VI. 
Experiments of dijlinguifhing and purifying Gold 
mixed with Platina. 
1. By Amalgamation with Mercury. 
Read Mar. 31, 
‘ 757 - 
I N an experiment related in the fourth 
paper, an amalgam of one part of 
platina and two of gold with a fuitable quantity of 
mercury, having been triturated with water for a 
confiderable time, and occafionally wafhed over, the 
platina was gradually thrown out, and the gold re- 
tained by the quickfilver. 
Repetitions of this experiment have {hewn, that 
tho’ the feparation fucceeds in fome cafes, it does not 
perfectly in all : that if there is any particle of the 
platina imperfectly diffolved in the gold (which will 
generally be the cafe, unlefs the quantity of gold is 
three or four times greater than that of the platina), 
this part will be retained, after long trituration, un- 
diffolved by the mercury, un comminuted by the 
peftle, and too ponderous to be wafhed off in its 
grofs form. A variety of mixtures of platina and 
gold were treated in the manner above defcribed j 
and the gold, recovered from the amalgams, fubmit- 
ted to further examinations. Where the proportion 
of platina was large, the microfcope almoft always 
difcovered (till fome granules of it on the fraCture of 
the 
