Chemist)']/ and Physics. 307 



next applied. A known mass of the positive material (which had 

 been washed and dried) was treated with an excess of a solution 

 of oxalic acid of known volume. The oxalic acid reduced the 

 higher lead oxide and the nitric acid, which was subsequently 

 added, transformed the lead into the nitrate. After all the mate- 

 rial had dissolved the excess of oxalic acid was estimated by the 

 aid of a titrated solution of potassium permanganate. Knowing 

 the volume of permanganate required to reduce the same volume 

 of the original solution of oxalic acid, it was a simple matter to 

 calculate the quantity of oxalic acid oxidized by the higher lead 

 oxide. Let Pb O x = formula of oxide in question, p = mass of 

 oxide used, p'= mass of oxalic acid necessary for oxidation, then 



(x - l)IT,C\O l + PbO v + 2HNO s = 



2{x- 1) CO, + xH % + Pl^OX 



207 4- 16a: 90(a; — 1) 



whence — = ; 



P P 



Experiment gave x = 2 - 3 so that the required formula for the 

 oxide becomes Pb^O.. 



This result is in complete accord with the mutually independent 

 ohservations of Tennen and Hollard on the electrolytic analysis 

 of solutions of nitrate of lead. In the formation of lead peroxide 

 the ratio Pbj PbO t has the observed value 0*853 instead of 

 O'Sini, when electrodes of unpolished platinum are used. The 

 smaller number corresponds to the same formula, Pb^O r 



This higher oxide obtained electronically was also analyzed 

 by reducing it in a current of hydrogen. This gave x = 2*37. 

 At the beginning, the reduction is very rapid and the color of the 

 powder changes from black to brown; near completion, it is 

 necessary to heat the glass vessel containing the substance. 

 When chemical lead dioxide was subjected to the same treatment 

 it was found that x = l - 96. This method should have given 

 x = 2, but a high degree of accuracy was not attempted in the 

 last experiment. 



The black substance which would accordingly have the formula 

 Pb % 1 is very unstable, and the author suggests that the higher 

 oxide which is present in the cells of the positive plate, when 

 completely charged, may be even more rich in oxygen. When 

 placed in a capsule, which was protected from the influence of 

 stray reducing dust, the black powder gradually turned brown in 

 the course of a few days, the change of color commencing at the 

 surface. Fery interprets this phenomenon as being due to the 

 spontaneous loss of oxygen and not to an alteration in the 

 physical state of the material. 



All the preceding evidence is strengthened by an experiment 

 of another kind. When a positive plate made by Plante's method 

 is discharged by means of a plate of zinc two distinct stages are 

 observed— the one, from 2*5 to 23 volts, corresponds to the pas- 

 sage from PbO x to PbO,; the other, between 0-7 and 0*3 volts, to 

 the reduction of Pb O a to the metallic condition. The capacity 

 of the second discharge is about four times greater than that of 



