Lead and Lead. Peroxide 181 
THE SIMULTANEOUS ELECTRO-DEPOSITION OF LEAD AND LEAD 
PEROXIDE. : 
M. G. MELLON and H. F. REINHARD. 
Part I—INTRODUCTION. 
General. For many years it has been known that one may obtain 
the deposition of either metallic lead upon the cathode or lead peroxide 
upon the anode by the electrolysis of an aqueous solution of lead nitrate, 
depending upon the conditions maintained during the electrolysis. Many 
experiments under varied conditions have shown that lead may be 
quantitatively deposited on the anode as the peroxide from a solution 
of the nitrate containing 10 to 20 per cent nitric acid of Sp. G. 1.35- 
1.40.1. A quantitative deposition of the lead in the metallic state has 
not. been accomplished from aqueous solutions of the nitrate except 
through the addition of other compounds, such as those recommended 
by St&hler and Alders.* They accomplished this by separating the lead 
as amalgam from a solution of the nitrate (0.0997 g. lead) and of mer- 
euric chloride (0.0855 g. mercury) together with 1 cc. of concentrated 
nitric acid and 1.5 cc. of phosphoric acid. Also Vortmann® states that 
lead can be quantitatively separated as an amalgam from a solution 
containing 1.4 g. of the lead salt, 1.2 g. mercuric chloride, 3-5 g. sodium 
acetate, 1 cc. of a concentrated solution of potassium nitrite, and enough 
acetic acid to dissolve any white precipitate formed. 
In connection with two other investigations‘ lead amalgams were used 
which were made by electrolyzing a 10 per cent solution of the nitrate 
with a weighed amount of mercury for the cathode and a platinum foil 
electrode for the anode. After electrolyzing for 2 to 3 hours with a 
current of approximately 20 milliamperes, sufficient lead was deposited 
in the mercury to show a considerable amount of solid along with the 
liquid amalgam. This solid was taken to be the compound Pb:Hg, 
described by Fay and North.’ A comparatively thick, adherent deposit 
of lead peroxide was always obtained on the anode. In this previous 
work a coulometer was included in the electrical circuit, the assumption 
being that a quantity of lead would be deposited in the mercury cathode 
equivalent in amount to the metal deposited in the coulometer. Then, 
knowing the weight of the lead deposited and the weight of the mer- 
cury, one could readily calculate the percentage composition of the 
amalgam. Such a procedure, with a silver coulometer, has been used 
by Henderson’ for zine amalgams, and by Richards and Wilson’ for 
1 Smith—Electro-Analysis, p. 109 (1918). 
2 Ber. 42, 2685 (1909). 
3Tbid. 22, 2756 (1891). 
4 Henderson and Stegeman—J. Am. Chem. Soc. 40, 84 (1918). Mellon and Hender- 
son—lIbid. 42, 676 (1920). 
5 Am. Chem. J. 25, 216 (1901). 
6 Phys. Rev. 29, 507 (1909). 
7 Carnegie Inst. Pub. 118, 1 (1909). 
