1383.] Chemistry of Storage Batteries. 69 



4th. The chemieal action on the coating of the negative plate : — 



S0 4 Pb + H 2 -f-20H 2 = Pb + S0 6 H 6 . 

 Lead sulphate. 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 snlphuric 

 acid, each molecnle of which throws upon the positive plate three 

 atoms of oxygen, and upon the negative plate six atoms or three 

 molecules of hydrogen. Each atom of oxygen decomposes one mole- 

 cule of lead sulphate on the positive plate, producing one molecule of 

 lead peroxide, and one of sulphuric anhydride, the latter instantly 

 uniting 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 : — 



1st. The electrolysis of hexabasic sulphuric acid as in charging. 



2nd. The reconversion of sulphuric anhydride into hexabasic sul- 

 phuric 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 : — 



Pb0 2 + H 2 = PbO + OH 2 . 

 Lead peroxide. Lead oxide. Water. 



The lead oxide thus formed is immediately converted into lead 

 sulphate : — 



PbO + S0 6 H 6 = S0 4 Pb + 30H 2 . 



4th. The chemical action upon the coating of what has now become 

 the positive plate of the cell : — 



Pb + + S0 6 H 6 =S0 4 Pb + 30H 2 . 



Thus in discharging, as in charging, a storage cell, the initial action 

 is the electrolysis of hexabasic sulphuric acid. The oxygen elimi- 

 nated on the positive plate reconverts the reduced metal of that 

 plate into lead oxide, whilst the hydrogen transforms the lead per- 

 oxide on the negative plate into the same oxide, which in both cases 

 is immediately converted into lead sulphate by the surrounding sul- 

 phuric acid, thus restoring both plates to their original condition 

 before the charging began. 



The real " 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 conducting metallic nucleus 

 of the plate. Lead sulphate itself has a very low conductivity, whilst 

 lead peroxide, and especially spongy lead, offer comparatively little 



