Lead in Lead Amalgam 189 
SOME EXPERIMENTS ON THE DETERMINATION OF LEAD IN LEAD 
AMALGAM. 
M. G. MELLON and H. F. REINHARD. 
In working with lead amalgams several types of procedure have 
been employed by various individuals for obtaining the concentration of 
the lead in the amalgams. These methods may be conveniently classi- 
fied as electrolytic, gravimetric, and physico-chemical. There follows a 
brief outline of the principles involved in the three types of procedure. 
Electrolytic Methods. One electrolytic method takes advantage of 
the scheme used for preparing the amalgam. Under certain conditions 
Stahler and Alders* found that lead deposits in a mercury cathode. 
They maintain that the amalgam formed may be washed with water, 
alcohol, and ether, and weighed. Knowing the original weight of the 
mercury serving as the cathode, the increase in weight represents the 
amount of lead deposited. From these two weights the concentration 
of the lead may be calculated. In using this procedure Vortmann’ 
encountered difficulties from the oxidation of the amalgam when the 
electrolyte was alkaline. The authors have had similar trouble when 
working with lead amalgams in which the lead was deposited from 
aqueous solutions of lead nitrate. The above procedure is ultimately 
a method of preparing an amalgam in which the concentration of the 
element deposited in the mercury is known, rather than a method of 
analysis. 
A somewhat similar method has been employed by Richards and 
Wilson’ for amalgams of thallium, indium and tin. As in the above 
method, the amalgams were prepared by depositing the different ele- 
ments electrolytically in a mercury cathode. The concentration of the 
metal deposited was obtained by means of a silver coulometer included 
in the electrical circuit during the electrolysis, the assumption being 
that the element deposited in the mercury was equivalent in amount 
to the silver deposited in the coulometer. The percentage composition 
of the amalgam could then be calculated from the weights of silver and 
of the mercury serving as cathode. 
A third electrolytic method is that suggested by Smith.* It in- 
volves the solution of the amalgam in nitric acid and the deposition of 
both elements. With properly arranged apparatus, and under suitable 
conditions, the lead deposits at the anode as the peroxide and the mer- 
cury at the cathode. 
Gravimetric Methods. The methods outlined here for the gravimet- 
ric estimation of the concentration of lead in lead amalgams involve 
1 Ber. 42, 2685 (1909). 
2Tbid. 22, 2756 (1891). 
3 Carnegie Inst. Pub. 118, 1 (1909). 
4 Blectro-Analysis, p. 229 (1918). 
Smith and Moyer—J. Anal. Ch. 7, 252 (1893); Z. anorg. Ch. 4, 267 (1893). 
Smith and Heidenreich—Ber. 29, 1585 (1896); Z. Elektrochem, 3, 151 (1897). 
