Apeil 27, 1883.] 



KNOWLEDGE 



249 





course, it would be a very feeble one and of short dura- 

 tion. Nevertheless it was from this that the first idea of 

 secondary batteries was suggested. 



In 1S.")9 M. Gaston Plante constructed an accumulator of 

 lead. He took two long strips of lead about 10 in. wide, 

 separated them from each other by means of pieces of 

 indiarubber, or tape, laid diagonally across between the 

 two, rolled them up together spirally, and immersed them 

 in a vessel of acidulated water. 



This battery acts also through the decomposition of 

 water : but not precisely in the same manner as the 

 platinum plates. If we now perform another experiment 

 and immerse two small plates of bright load in acidulated 

 water, then pass the current from two Grove cells through 

 this small battery, we shall find that gas is not evolved at 

 first from both plates, but only from the one attached to 

 the zinc or minus pole of the charging source, while the 

 other becomes of a brown colour. When circuited through 

 the galvanometer, we obtain a current of longer duration 

 than in the case of the platinum plates. Suppose we re- 

 peat the process of charging and discharging several times, 

 first charging the plates in one direction, then discharging, 

 and charging in the other direction, and so on. After some 

 time, let us charge only in one direction, when, on dis- 

 charging through the galvanometer, we find that we obtain 

 a current for a far longer period of time than we did at 

 first ; when, on examining our plates, the one attached to the 

 plus pole of the charging battery is found to be thickly 

 covered with a layer of brown material, while the other 

 is in a more spongy state than when we commenced 

 aperations. 



The difference in the chemical action which occurs in the 

 two cases is that when the two plates of platinum were em- 

 ployed, platinum being a metal not attacked by free or 

 nascent oxygen, the secondary action was obtained simply 

 from the gases that were in close contact with, and to a cer- 

 tain extent occluded in, the surface of the platinum, the 

 effect of which could be increased by rendering this surface 

 alightly spongy ; while in the case of the lead plates, lead 

 being an easily oxidisable metal, the oxygen attacked the 

 lead at the anode, or plate connected to the plus pole of 

 the charging source, forming peroxide of lead (PbO^,), 

 while at the cathode, or plate attached to the minus pole of 

 the charging source, the hydrogen was given off in bubbles, 

 provided the plate was quite bright ; if, however, it was 

 oxidised or partially converted into sulphate before charg- 

 ing, this oxide or sulphate was reduced by the hydrogen to 

 metallic lead. The reason for alternately reversing the 

 direction of the current in charging is that the peroxide of 

 lead at the anode, which, when the battery is discharged, 

 becomes converted principally into sulphate and a lower 

 oxide, on recharging in the reverse direction should become 

 reduced to metallic lead in a spongy condition, and thus be 

 more easily acted upon at the next time of charging. 



This process of continually charging, discharging, and 

 recharging in the opposite direction is called forming the 

 battery, and when it is continued until the plates are 

 rendered of a spongy nature nearly through their entire 

 thickness, the Plante battery is in its best condition. 



This forming of the plates in the case of a large cell 

 takes about eight months, which renders it rather a tedious 

 and expensive process ; so another Frenchman, M. Camille 

 Fanre thought he would obviate the inconvenience by 

 mechanically coating the plates with an oxide of lead, such 

 as litharge (PbO). or minium, or red-lead (Pb^Oj), which, 

 when once reduced, would give a coating of spongy lead in 

 contact with the lead plates. 



Plates of lead were taken, spread over with a paste of 

 red-lead and dilute sulphuric acid, and sewn up in felt 



cases; a number of these plates were then laid side by side, 

 the odd numbers connected to one terminal, and the evert 

 to another; they were then immersed in a vessel containing 

 dilute sulphuric acid, and charged in the usual way, but 

 the current was only reversed once or twice. 



To understand the chemical action of a Faure cell, let us 

 first suppose that the plates are coated with litharge (Pb O), 

 or plumbic oxide, and are immersed in water (the reason 

 dilute acid is employed being that water is such a very 

 bad conductor witliout the addition of a certain quantity of 

 acid ; but, as far as the theory is concerned, we can suppose 

 we are dealing with water alone.) 



PbO 



HoO HP HoO PbO 



Pb OH. OH, OH, OPbO ^ 

 Pb H,b H,ij H,0 PbO; 



When a current is passed through the cell in the direc- 

 tion of the arrow, the water is decomposed, hydrogen being 

 given off at the cathode, and oxygen at the anode. The 

 hydrogen reduces the PbO by combiuing with its oxygen to 

 form water, while the oxygen liberated at the anode com- 

 bines with the PbO there to form PbO., or peroxide of 

 lead. 



Practically, then, the oxygen combined with the plumbic 

 oxide at the cathode has travelled over to the anode to 

 peroxidise the plumbic oxide there in charging, and on dis- 

 charge, this oxygen travels back to the cathode, lea\-ing 

 Pb O on both plates as at starting. 



Now, to take a case that is more likely to occur in 

 practice ; suppose we take a discharged cell that contained, 

 when charged, dilute sulphuric acid (H,SOj) as the electro- 

 lyte, we have on both plates lead sulphate (PbSO^), and 

 if the dilute acid in the cell was fairly weak, it becomes 

 practically water when the cell is entirely discharged. 



S04H, OH. OH; I gQ^^ 



t Pb SO^H- OH, OH.SOj PbO.. 

 \ Pb H.SOj H;6 n,S04 PbO. 



We start with lead sulphate on both plates and water as 

 the electrolyte ; the hydrogen liberated at the cathode 

 reduces the PbSO, by combining with the SO^ radical, 

 while the O liberated at the anode combines with a mole- 

 cule of water of the PbSO^ thus — 



O -f PbSO, -f HoO = PbO, + H.,SO,. 

 As the charging continues, the acid in the cell gradually 

 becomes stronger, till the cell is entirely charged, when we 

 have the PbSO, converted into lead at the cathode, and 

 into peroxide of lead at the anode, while all the S O, that 

 was in combination with it has combined with the hydrogen 

 of the water forming H; 8 Ot or sulphuric acid. 



In practice it is, however, exceedingly difficult to reduce 

 pure lead sulphate with an electrolyte of dilute acid, on 

 account of the bad conductivity of the salt lead sulphate. 



It will thus be seen from this description of the theo- 

 retical chemical action which goes on in the charging of an 

 accumulator, that it is absurd to speak of a secondary 

 battery as storing electricity ; energy in the form of a 

 current of electricity in charging produces chemical action, 



