Lead and Lead Peroxide 183 
methods for the determination of the lead peroxide on the anode, the 
metallic lead in the mercury of the cathode, and the metallic silver in 
the coulometer. 
*ParT JJ—EXPERIMENTAL PROCEDURE AND DATA. 
Fig. i 
Apparatus. The arrangement of apparatus used is illustrated by 
Fig. 1, in which A, A’ represent special glass cells containing the solu- 
tion of lead nitrate—these were about 6 cm. in diameter and of such 
a form that 40 g. of mercury easily covered the platinum points in the 
bottom; B, B’ are anodes of platinum foil 2.5 cm. in diameter and 5 
cm. in length; C, C’ are the mercury cathodes, the electrical contact 
being made with them by means of three short pieces of platinum wire 
sealed through the glass; D is a platinum dish 7 cm. in diameter serv- 
ing as the cathode in the silver coulometer; E is the porous cup, 3.5 
cm. in diameter, and F the anode of 15 gauge coiled silver wire; G is 
an adjustable rheostat; H a milliammeter and I a storage cell. 
Analytical Methods. The weight of silver deposited was deter- 
mined by weighing the platinum dish after drying to constant weight 
at 105° C. 
In order to determine the lead in the deposit of peroxide, the orig- 
inal intention was to follow the volumetric method suggested by Scott. 
This consists in dissolving the peroxide from the electrodes with a hot 
mixture of 15 cc. of fifth normal oxalic acid and 10 cc. of nitric acid 
(Sp. G. 1.2) and titrating the excess of oxalic acid with tenth normal 
potassium permanganate. The end point in the titration with the 
potassium permanganate proved to be so indefinite that the method 
9 
was abandoned for a procedure essentially that recommended by Smith.’ 
1 Standard Methods of Chemical Analysis, p. 240 (1917). 
Chwala and Colle—Z. anal. Chem. 50, 209 (1911). 
2 Loe. cit. 
