Additional Notes on Secondary Batteries. 43 



which lie expressed by the formula S 2 Pb 3 O 10 . He adduces, 

 however, no evidence to show that it is not a mixture of 

 Pb0 2 with 2PbS0 4 . We sought for some means of deciding 

 between these two views. A solution of acetate of ammonium 

 is known to dissolve sulphate of lead, and was in fact used 

 long ago for that purpose. It might therefore be expected 

 to separate the sulphate from the peroxide, while it was not so 

 likely to bring about the decomposition of such a compound 

 as S 2 Pb 3 Oio. 



Some of the red substance was prepared by treating 

 minium with an excess of dilute sulphuric acid (1 of acid 

 to 10 of water). After four days the action was still in- 

 complete, but eventually it absorbed the full amount of acid 

 required by theory. 



The percentage of lead in the resulting red substance was 

 just over 72 per cent. 



A portion of this, after treatment with a 3 per cent, solution 

 of acetate of ammonium, left a residue which was much 

 darker in colour than the original and contained 82 per cent, 

 of lead. That is to say, it was approximating towards Pb0 2 , 

 which contains 86*6 per cent, of lead. The liquid was colour- 

 less, and the ratio between the Pb and S0 4 dissolved was 

 determined in several different instances. The ratio 



Weight of Pb 

 Weight of S0 4 



varied from 2*0 to 2' 15, pure PbS0 4 requiring 2*16 and 

 Frankland's compound 3*23. The portion dissolved there- 

 fore was not a basic sulphate, and the evidence tells against 

 the original substance being a chemical compound. 



Of course, it is impossible to affirm that no subsulphate is 

 ever formed in the reactions of a secondary cell, but all that 

 we actually know is perfectly consistent with the old and 

 simpler supposition that PbS0 4 is the salt alternately formed 

 and decomposed. 



Action of Sulphuric Acid on Lead. 



In our former communication we described a comparative 

 experiment in which dilute sulphuric acid, either alone or 

 mixed with a small quantity of sodium sulphate, was allowed 

 to act on spongy lead. The experiment was allowed to con- 

 tinue for five months, and hydrogen gas was given off for 



