222 
Planté and its modifications. Our attention was very 
naturally directed to the chemical changes that take place 
in these batteries, especially as it appeared to us that 
there must be certain analogies between them and some 
actions which we had previously investigated. In the 
present communication we propose to treat merely of one 
point—that of local action, leaving the fuller discussion 
of the subject to some future occasion. 
It is well known that metallic zinc will not decompose 
water even at roo’ C., but we found that zinc, on which 
copper had been deposited in a spongy condition, was 
capable of splitting up the molecule even at the ordinary 
temperature, oxide of zinc being formed and hydrogen 
liberated. If placed in dilute sulphuric acid, it started a 
very violent chemical action, sulphate of zinc and hydro- 
gen gas being the result. We termed the two metals thus 
conjoined, the copper-zinc couple, and this agent was 
fruitful in our hands in bringing about other chemical 
changes which neither metal singly would effect. Elec- 
tricians will readily understand the nature of this agent, 
and will recognise in its effects only a magnified form of 
what we are all familiar with under the name of doca/ 
action. Now the negative plate of a Planté secondary 
battery is a sheet of lead, upon which finely-divided 
peroxide of lead is distributed. It is well known that 
the electromotive force of lead and lead peroxide in dilute 
sulphuric acid is nearly three times that of zinc and 
copper in the same liquid. We were therefore induced 
to think that the plate must act in the same way as our 
copper-zinc couple. We found such to be the case. If 
a plate so prepared be immersed in pure water, the de- 
composition of the liquid manifests itself by the reduc- 
tion of the puce-coloured peroxide to the yellow monoxide. 
There could be little doubt therefore that the lead perox- 
ide couple, if we may call it so, would decompose sul- 
phuric acid, with the production of sulphate of lead. 
This also was found to be the case. 
As the destruction of peroxide of lead means so much 
diminution of the amount of electric energy, it became 
interesting to obtain some definite knowledge as to the 
rapidity or extent of this action. 
When the peroxide of lead on the metal is very small 
in quantity, its transformation into the white sulphate 
goes on perceptibly to the eye, but when the coating is 
thicker, the time required is, as might be expected, too 
long for this kind of observation. In one experiment, fol- 
lowing the procedur2 of Planté, we formed the peroxide 
on the plate by a series of seventeen charges and dis- 
charges, or reversals, each operation lasting twenty 
minutes, and the time was further broken up by seven 
periods of repose, averaging about twenty-four hours in 
length. After the last charge we watched the local action 
taking place, and found that the whole of the peroxide 
passed into white sulphate within seventeen hours. In 
another experiment the two plates formed according to 
Planté’s method were immediately joined up with the 
galvanometer, and the deflection noted. ‘Jhey were then 
at once disconnected. After the repose of one hour they 
were joined up again, and another observation taken 
with the galvanometer. This was repeated several times, 
with the following results :— 
Initial strength of current ... 100 
(AStEriE MOU SiTEPOSE x... ces. col ses suc 
» 2 ” ee Yer ey YC 40 
oy = Sth e © hs ee 
vy 17 ” . 1°5 
It results from this that during each of the long periods 
of repose recommended by Planté the peroxide on the 
lead plate is wholly, or almost wholly, destroyed by local 
action, with the formation of a proportionate amount of 
sulphate. But this is not, as it would seem at first sight, 
a useless procedure; for, in the next stage, the sulphate 
is reduced by electrolytic hydrogen, and, by a process 
which we hope to explain when discussing the complete 
NATURE 
history of the reaction, the amount of finely divided lead 
capable of being peroxidised is increased. That this is 
actually the case is shown by the following experiment. 
The peroxide formed on a lead plate by first charging 
was determined and called unity: it was allowed to 
remain ina state of repose for eighteen hours, charged a 
second time, the peroxide again determined, and so 
on :— 
Separate periods of repose. Charge. Amount of peroxide. 
— 5 First vas. cee ED) 
18 hours Second 1'57 
2 days Third 1°71 
eae Fourth 2°14 
yee Fifth 2°43 
In other trials, following the procedure of Faure, we 
employed plates in which the peroxide was formed by the 
reduction of a layer of red lead (containing 51 grains to 
one square inch of metallic surface) and subsequently 
completely peroxidising the spongy metal so produced. 
In one series of experiments we left the peroxidised plates 
to themselves for various periods and determined the 
amount of sulphate formed. This gave us the amount of 
peroxide consumed. 
Experiment I. after 2 hours 7°2 per cent. 
” Le %” 3 ” 15 I ” 
” Ill. ” 4 ” 198 ” 
» TM Sass SOO” ae 
99 ive ” 24 ” 36°3 ” 
an VI. ,, 7 days 583 a 
5p mo WLe egy eX eO 7-9 Ww 
99> VEE ye 5 7453) 
The last experiment was tested with the galvanometer 
during its continuance, as in the case of the plate formed 
by Planté’s method, with the following results :— 
Tnitial strength of current 100 
After Tudays/ 6epose) esse vse. san, oes 
” Set ” SA Psy eno 79 
” 4 oo» ” Sabh i Kane acces Jaan 34 
” 5 aos ” Sa, Minne? aes) Mracs 7 
” 7 ” ” 
» 9 » 9 8 
» I 
It is evident from these observations that a lead- 
peroxide plate gradually loses its energy by local action, 
and that the rate varies according to the circumstances 
of its preparation. 
Two difficulties will probably present themselves to 
any one on first grasping the idea of this local action :— 
1. Wby should a lead plate covered with the peroxide 
and immersed in dilute sulphuric acid, run down so 
slowly that it requires many hours or even days before 
its energy is so seriously reduced as to impair its value 
for practical purposes? In the case of the copper-zinc 
couple immersed in the same acid, though the difference 
of potential is not so great, a similar amount of «hemical 
change would take place in a few minutes. 2. In a 
Planté or Faure battery the mass of peroxide which is in 
contact with the metallic lead plate expends its energy 
slowly. How comes it to pass that if the same mass of 
peroxide be brought into connection through the first 
lead plate with another lead plate at a distance, it ex- 
pends its energy through the greater length of sulphuric 
acid in a tenth or a hundredth part of the time? 
The answer to these two questions is doubtless to be 
found in the formation of the insoluble sulphate of lead, 
which clogs up the interstices of the peroxide and after a 
while forms an almost impermeable coating of high 
resistance between it and the first metallic plate. 
The following conclusions seem warranted by the 
above observations :— 
In the Planté or Faure battery local action necessarily 
takes place on the negative plate, with the production of 
sulphate of lead. 
The formation of this sulphate of lead is absolutely 
” ) . ee Ge I 
