April 12, 1883 } 
NATURE 
569 
part ; whilst others assert that no chemical change of this sulphate 
occurs either in the charging or discharging of the plates. 
To test the first of these opinions, I made two plates of strips 
of thin lead twisted into corkscrew form, and af er filling the 
gutter of the screw with minium, so as to forma cylinder that 
could be afterwards introduced intoa piece of combustion-tubing, 
these plates were immersed in dilute sulphuric acid and charged 
by the dynamo-current in the usual manner, The charging was 
continued until the whole of the minium on the + and — plates 
respectively was converted into lead peroxide and spongy lead, 
and until gas bubbles streamed from the pores of the two 
cylinders, 
After removal from the acid the plates were superficially dried 
by filter-paper, and immediately introduced into separate pieces 
of combustion-tubing previously drawn out at one end, su as to 
form gas delivery tubes. The wide ends of these tubes were 
then sealed before the blowpipe, care being taken not to allow 
the heat to reach the inclosed cylinders. The tube containing 
the cylinder of reduced lead was now gradually heated until the 
lead melted, the drawn-out end of the tube meanwhile dipping 
into a pneumatic trough. The gas expelled from the tube con- 
sisted almost exclusively of the expanded air of the tube and 
contained mere traces of hydrogen, 
The tube containing the cylinder of lead peroxide was simi- 
larly treated, except that the heat was not carried high enough 
to decompose the peroxide. Mere traces, if any, of occluded 
oxygen were evolved. 
These results justify the conclusion that occluded gases play 
practically no part in the phenomena of the storage cell. 
With regard to the function of lead sulphate in storage bat- 
teries, I have observed that during the so-called ‘‘ formation” 
of a storage cell a very large amount of sulphuric acid dis- 
appears from the liquid contents of the cell: indeed, sometimes 
the whole of it is withdrawn. The acid so removed must be 
employed in the formation of insoluble lead sulphate upon the 
plates which, in fact, soon become coated with a white deposit 
of the salt, formed equally upon both positive and negative sur- 
faces. This visible deposit is, however, very superficial, and 
does not account for more than a very small fraction of the acid 
which actually disappears from solution. The great bulk of the 
lead sulphate cannot be discovered by the eye, owing to its 
admixture with chocolate-coloured lead peroxide, 
Unless the coated plates have been previously immersed for 
several days in dilute sulphuric acid, this disappearance of acid 
during their ‘‘ formation” contiaues for ten or twelve days. At 
length, however, as the charging goes on the strength of the 
acid ceases to diminish and soon afterwards begins to augment. 
The increase continues until the maximum charge has been 
reached and abundance of oxygen and hydrogen gases begin to 
be discharged from the plates ; that is to say, until the current 
is occupied exclusively, or nearly so, in the electrolysis of hexa- 
basic sulphuric acid expressed by Burgoin in the following 
equation :— 
Eliminated on Eliminated on 
+ plate. — plate. 
Mee Lee 
SO,H, = SO; + 30 + 3H,. 
Sulphuric acid. Sulphuric 
anhydride. 
Of course the sulphuric anhydride immediately combines with 
water and regenerates hexabisic sulphuric acid :— 
SO, + 30H, = SO,Hg. 
On discharging the cell the specific gravity of the acid con- 
tinually decreases until the discharge is finished, when it is 
found to have sunk to about the same point from which it began 
to increase during the charging. Hence it is evident that during 
the discharge the lead sulphate, which was continuously decom- 
posed in charging, was continuously reformed in discharging. 
The chief if not the only chemical changes occurring during 
the charging of a storage battery, therefore, appear to be the 
following :— 
ist. The electrolysis of hexabasic sulphuric acid according to 
the equation already given. 
2nd, The reconversion of sulphuric anhydride into sulphuric 
acid. 
3rd. The chemical action on the coating of the + plate. 
SO,Pb + O+30H, = PbO, + SOgHg. 
Lead sulphate. Lead peroxide. Hexabasic 
sulphuric acid. 
4th. The chemical action on the coating of the negative 
plate :-— 
SO,Pb + 
H,+ 20H, = 
« Lead sulphate. 
Phy -e SO,H;. 
Hexabasic 
sulphuric acid, 
If I have correctly described these changes, the initial action 
in the charging of a storage cell is the electrolysis of hexabasic 
sulphuric acid, each molecule of which throws upon the positive 
plate three atoms of oxygen, aud upon the negative plate six 
atoms or three molecules of hydrogen, Each atom of oxygea 
decompo-es one molecule of lead sul ha'e on the positive plate, 
producing one molecule of lead peroxide, and one of sulphuric 
anhydride, the latter instantly unitinz with three molecules of 
water to form hexabasic sulphuric acid. 
The following are the chemical changes which I conceive to 
occur during the discharge of a storage cell :-— 
Ist. The electrolysis of hexabasic sulphuric acid as in 
charging. 
2nd. The reconversion of sulphuric anhydride into hexabasic 
sulphuric acid as already described. 
3rd. The chemical action upon the coating of what was before 
the positive plate or electrode, but which now becomes the 
negative plate of the cell, that.is to say, the plate from which the 
positive current issues to the external circuit :— 
PbO} eels = EDO 
Lead peroxide. Lead oxide. 
OB,. 
Water. 
The lead oxide thus formed is immediately converted into lead 
sulphate :— 
PbO + SO,H, = SO,Pb + 30H. 
4th. The chemical action upon the coating of what has now 
become the positive plate of the cell :— 
Pb + O + SO Hg = SO,Pb + 30H. 
Thus in discharging, as in charging, a storage cell, the initial 
action is the electrolysis of hexabasic sulphuric acid. The oxygen 
eliminated on the positive plate reconverts the reduced metal of 
that plate into lead oxide, whilst the hydrogen transforms the 
lead peroxide on the negative plate into the same oxide, which 
in both cases is immediately converted into lead sulphate by the 
surrounding sulphuric acid, thus restoring both plates to their 
original condition before the charging began. 
The reali ‘‘ formation” of the cell consists, I conceive, in the 
more or less thorough decomposition of those portions of the 
lead sulphate which are comparatively remote from the conduct- 
ing metallic nucleus of the plate. Lead sulphate itself has a 
very low conductivity, whilst lead peroxide, and especially 
spongy lead, offers comparatively little resistance to the current, 
which is thus enabled to bring the outlying portions of the 
coating under its influence. It may be objected that, during the 
discharge, the work of formation would be undone; but 
probably, in the ordinary use of a storage battery, the discharge 
is never completed. Thus I have found that, ina small cell contain- 
ing two plates 6” x 2”, short circuiting with a thick copper wire for 
twelve hours was far from producing complete discharge, for on 
breaking this short circuit the cell zstantly rang violently an 
electric bell with which it was previously connected. In ordinary 
discharges of ‘‘formed” cells, therefore, the lead sulphate on 
the positive and negative plates still remains mixed with 
sufficient lead oxide and spongy lead respectively to give it a 
higher conducting power than the sulphate alone possesses. 
2. Chemical Estimation of the Charge in a Storage Cell_—No 
method has hitherto been known by which the charge in a 
storage cell could be ascertained without discharging the cell ; 
but the results of the foregoing experiments indicate a very 
simple means of ascertaining the amount of stored energy without 
any interference with the charge itself. The specific gravity 
and consequent strength of the dilute sulphuric acid ofa ‘‘formed” 
cell being known in its uncharged and also in its fully charged 
condition, it is only necessary to take the specific gravity of the 
acid at any time in order to ascertain the proportion of its full 
charge which the cell contains at that moment; and if the duty 
of the cell is known, the amount of energy stored will also be 
thereby indicated. In the case of the cell with which I have 
experimented, containing about seven quarts of dilute sulphuric 
acid, each increase of ‘005 in the specific gravity of the dilute 
acid means a storage of energy equal to 20 amperes of current 
for one hour, obtainable on discharge. 
I hope shortly to be able to express, in terms of current from 
the cell, the definite relation between the amount of energy 
stored and the weizht of sulphuric acid liberated, 
