1891.] PlanU Cell from a Chemical Stand-point. 107 



strength used in batteries, and which is probably formed by secondary 

 action from per sill phuric acid. 



Mr. Preece most kindly aided the investigation by allowing experi- 

 ments to be carried out at the General Post Office, where one-half of 

 the secondary cells contain 1 per cent, of sodium sulphate and the 

 other half ordinary dilute acid, sp. gr. 1180. He also put at the dis- 

 posal of the author the records of the behaviour of the cells, and as 

 they showed that there was much less sulphating with sodium 

 sulphate, as shown by the sp. gr. never falling to the same extent as 

 in the plain cells, but that the general character of the changes in 

 temperature and in sp. gr. during charge and discharge were the 

 same in both types of cell, and of the nature which the work of Pro- 

 fessor Ayrton and others has rendered familiar to all, it was only the 

 distribution of temperature and of sp. gr. which was investigated, and 

 this was found to be very irregular. 



It was found that the addition of sodium sulphate, in about the 

 proportion of 1 per cent., to freshly electrolysed acid, or during 

 electrolysis, always produced a diminution in the total quantity of 

 " active oxygen," and brought the amount present in the plain cells 

 down almost exactly to that found in the sodium sulphate cells. 



Experiments on the growth of the " peroxides " were carried on 

 during five charges and discharges, but only the figures relating to 

 the first discharge are given, as the other charges and discharges are 

 mere repetitions. The peroxides form at once, then undergo a 

 diminution, and then increase again. The alteration in the totals is 

 due mainly to actions occurring at the lead plate in tbe plain cell, as 

 at the peroxide plate the amounts steadily increase ; in the sodium 

 sulphate electrolyte there is a diminution at both plates, followed by 

 an increase. 



Determinations were made of the amounts of " active oxygen " 

 present as persulphuric acid and hydrogen dioxide respectively, and 

 it was established that acid taken from the cell reduced peroxide of 

 lead. The presence of hydrogen dioxide being thus established both 

 directly and indirectly, its effect on the E.M.F. of a cell was tested. 

 It was found that, while its addition to the acid in the case of a lead 

 peroxide couple in dilute sulphuric acid produced an annulment or 

 reversal of the E.M.F. , the introduction of hydrogen dioxide into the 

 body of the peroxide paste produced an increase of E.M.F. in the case 

 of a platinum-lead peroxide couple. 



The latter experiment was made with a view of reproducing, if 

 possible, the conditions of a cell which is started discharging directly 

 it is fully charged, and in which the persulphuric acid formed at the 

 positive during charge may be supposed to break up with the forma- 

 tion of hydrogen dioxide on the cessation of the charging current, 

 thereby increasing the normal E.M.F. of the cell. 



