308 



The Chemistry of Storage Batteries. [June 20, 



II. In discharging — 



(a.) Positive Plates. 

 5Pb0 2 + 3S0 4 H 2 + 5H 2 = S 3 Pb 5 14 +80H 2 . 



(6.) Negative Plates. 

 5Pb + 3S0 4 H 2 + 5 = S 3 Pb 5 14 + 30H 2 . 



If the red lead salt be the active material, then the following equa- 

 tions express the same electrolytic reactions :— 



I. In charging — 



(a.) Positive Plates. 

 S a Pb 8 O 10 + O s + 2OH a = 3Pb0 2 + 2S0 4 H 2 . 



Eed lead Lead Sulphuric 



salt. peroxide. acid. 



(b.) Negative Plates. 

 S 2 Pb 3 O 10 + 4H 2 = 3Pb + 2S0 4 H 2 + 20H 2 . 



II. In discharging — 



(a.) Positive Plates. 

 3Pb0 2 + 2S0 4 H 2 + 2H 2 = S 2 Pb 3 O 10 + 4OH 2 . 



(b.) Negative Plates. 

 3Pb + 2S0 4 H 2 + 20 2 = S 2 Pb 3 O 10 -f 20H 2 . 



An inspection of these equations discloses, in the case of the red 

 lead salt, a fact which has already been ronghly observed in practice, 

 viz., that only half as much active material is electrolytically decom- 

 posed on the negative as on the positive plates ; whence it follows 

 that the weight of active material on the negative plates need not 

 exceed one-half of that upon the positive plates ; for, in the decom- 

 position of the electrolyte, equivalent quantities of oxygen and 

 hydrogen are evolved ; that is to say, two atoms of hydrogen for each 

 atom of oxygen. But, in the decomposition of the red lead salt, four 

 times as many atoms of hydrogen are required to reduce the salt to 

 metallic lead as atoms of oxygen which are necessary to transform 

 the lead of the salt into peroxide. When, however, the active 

 material of the positive plate has once been converted into peroxide 

 of lead, it seems probable that the red salt only is formed ; at all 

 events until the discharge at high potential is nearly completed, when 

 there are indications of the production of the buff-coloured salt. But 

 this is a point requiring further investigation. 



I have to thank Dr. ¥. R. Japp, F.R.S., for his assistance in the 

 analytical work of this investigation. 



