Feb. 16, 1882] 
NATURE 363 
through the solid sulphate, which it oxidises and decomposes, 
to reach the lead, to the total exclusion of the liquid channel 
through which it ordinarily attacks it, although liquid contact 
may very possibly be needed with the sulphate at its oxidation 
oint. 
Another unexpected feature presented itself, which perfec'ly 
confirms this view. My current source being a hand-gramme 
machine, turned by a water-turbine, which permits easy regula- 
tion of the current strength and tension by adjusting the water- 
tap, it was kept low at first, let the discharge of oxygen- 
bubbles from the lead shot should project upwards some of the 
settled powder into the liquid, and disturb its clearness, But 
no such ill effects having occurred while the current’s strength 
was cautiously increased during the first half hour, it was then 
finally raised to the fu'l charging power of the turbine, taking 
up a wheel-speed, and tension of the current showing a slightly 
greater resistance in the cell than one of the same size made 
with rolled up piates would have offered to the machine-current. 
With this full tension of two or three Grove’s cells, bubbles of 
oxygen soon formed round the shots, but instead of this gas 
escaping turbulently through the powder, it collected under it 
until of sufficient volume to find an intermittent passage round it 
at one corner of the cell, and through an accidental hole or crevice 
in the middle of the layer, without producing the least turbidity in 
the cell’s quite recently deposited contents! ‘The layer’s uneven 
surface was also not at all disturbed by a little agitation of the 
cell, showing that it had acquired considerable consistency by 
the action of the charging current. Of this effect of the treat- 
ment, the passage of a current into and through the sulphate of 
the layer, during its process of oxidation, would, it seems 
probable, be a sufficient explanation. No return-current could 
at this stage be extracted from the cell, which is also the case at 
the outset im forming, by a constantly directed exciting current, a 
Faure’s accumulator. The charging-current was therefore left 
running for the night, the shot-layer having well imbued itself 
in a froth of white particles under the dark roof above. The 
effect of current-reversal was, however, first tested, with the 
result, after a short duration, of dissipating the white sediment, 
and exposing again the bright surfaces of the amalgamated shot, 
while the counter-plate above acquired as usual, under such 
conditions, a thick Planté’s coating of dark oxide. ‘lhis was 
discharged, as may always be done when it makes its appear- 
ance, as a secondary current of some strength ringing a call-bell 
for no inconsiderable portion of a m‘nute. The shots remained 
bright, and exhibited no visible alteration. The charging- 
current was reinstated, and they soon covered themselves again 
with the mantle of white froth and powder as described. 
On the following morning a great transformation had 
occurred. Only a few specks of white sulphate remained 
undecomposed in the corners of the cell; the rest had all 
blackened, nearly hiding the shots, and separated by no definite 
line of demarcation from the now clod-like layer of what had 
been the minium-coat above. The latter really resembled grey 
and black earth-clods mixed together, the black or dark humus 
brown ones forming continuous extensions of the similar con- 
verted sulphate underneath, and the grey admixture being 
apparently the originally separated binoxide of the minium 
layer placed in the cell at starting. A secondary, or return 
current was obtained from the cell in this condition, which rang 
a call-bell strongly for seven minutes. No visible alteration of 
colour or other change of appearance in the materials furnishing 
this current at the bottom of the cell could be perceived while it 
was being extracted from them. 
_ The charging-current was then applied again, and remained 
in constant action (during which time it was not visited) for 
twenty-four hours. On this second morning the blackening was 
so complete, that not only were the shots hidden, but the nether 
line of the top coat of minium was no longer distinguishable. 
The dark humus-like transformation of the sulphate enveloped 
the former, and penetrated the latter, leaving ouly some large 
insular grains and clods of the grey substance of the upper layer 
still unaffected, as if untraversed by the current’s charging or 
compacting action, The duration, however, of the secondary 
current now yielded by the cell was still only seven minutes, as 
before ; and no increase of storage capacity was therefore given 
to it by this long additional, and to all appearance strongly 
operative period of oxidising direct excitation. The materials 
as before underwent no visible change of aspect during the 
extraction of the secondary current. 
The cell, evidently quite formed, was now once more filled to 
test its retentiveness, After a few hours of charging, the rough 
dendrites of humus-coloured substance acquired frond-like form 
and much greater compactness as they shrank asunder and ap- 
proached apparently the ceramic and brittle state of consolida- 
tion which the coating of the Faure accumulator plates exhibits 
when they have been once or twice recharged. The shot-cell 
proved perfectly retentive of its charge, and although only a 
poor substitute for one of folded or rolled up plates, in storage 
capacity and in freedom from resistance it is yet a very fairly 
efficient accumulator. From the simplicity of its construction, 
and from the easy inspection which it permits of the several 
stages of the process of red-lead primary excitation, I can com- 
mend its use to those who are busily engaged, like myself, in the 
difficult and complicated study of the question of secondary 
battery improvements, 
The tendency to cohere and harden which binoxide of lead 
possesses when formed by and submi'ted to a current, is well 
proved by the iridescent hues which it exbibits when deposited 
in the form of Nobili’s rings on some bright metals, such as 
clean platinum and german silver, the optical explanation of 
which points to the existence of a good reflecting surface in the 
film. A similar reflecting surface is found to exist, for oblique 
incidences of light, in the opaque layer of soot of a candle-flame 
on smoked glass ; and it may be that this optical character of 
such deposits which cannot be perceived by the microscope to 
be granular, is not physically unconnected with the electrical 
properties of the film which, in the case of binoxide of lead, 
give it capacity for storage in the chemical form of the energy 
of the secondary current. And yet it is not only by enlarging 
the area of the coherent binoxide film, and extending the surface 
of lead over which it is spread, that increase of storage capacity 
can be given to corrugated or to spongily and otherwise rough- 
ened lead elements ; but it appears also to be attainable, at least 
in some degree by increasing the thickness of the film; for on 
reyersing the exciting current of the lead-shot cell, for the second 
time only, so as to oxidise the coxnter-plate, the secondary or 
return current taken from this plate rang the call-bell continu- 
ously for twenty minutes, which denoted a storage capacity in 
the little exposed surface of the small lead-plate nearly three 
times as large as any before arrived at in the thick layer of shots 
at the bottom of the cell. A. S, HERSCHEL 
College of Science, Newcastle-on-Tyne, January 28 
P.S.—It appears to be the hydrogen occluded in the positive 
plate as much as the oxygen stored up on the negative one that 
gives the Planté and the Faure cells their secondary voltaic 
power ; for on trying several metals as the positive } late in the 
shot-cell, after charging it again directly to its full capacity, I 
found their order as regards the strength of the secondary, or 
return current obtainable with them from the charged cell to be 
as follows :— 
Clean lead : a feeble current, only traceable with a galvano- 
meter. Amalgamated lead gave the same. 
Copper : a pretty strong current, which easily rings the call- 
bell. 
Hydrogenised lead (the counterplate used in charging the cell 
directly) : a strong current, ringing the bell loudly, and giving a 
spark between its wires. 
Hydrogenised platinum (prepared like the last lead plate): at 
first a strong current like the last, but degrading gradually, and 
not inferior in duration or storage capacity to that of the last 
lead-plate ! 
Amalgamated zinc: a very powerful current, far exceeding 
the preceding ones, and capable of maintaining the motion of 
the Gramme machine and water-wheel when the water was 
turned off, which only a well-made Faure cell of twenty-five 
square-inch plates rolled together had enabled me to accomplish 
before. Yet the area of the zinc strip used as a counterplate in this 
cell was scarcely so much as two square inches ! 
It is, no doubt, to the insignificance of the clean-lead current 
and to the consequent practical suppression of local currents on 
the negatively-charged plate, that lead secondary cells owe their 
astonishing retentiveness. It also deserves attention that, from 
the proof of these experiments, a provision for fixation of hydro- 
gen on the positive plate of lead cells must be made, equal in 
storage capacity to that which the binoxide furnishes for oxygen 
onthe other plate. Both lead and platinum, it seems however, 
are equally capable of furnishing this lodgment for hydrogen 
without any special preparation by a previous conversion to the 
spongy state. 
