106 Mr. G. fl. Robertson. A Study of the [June 11, 



It was to be expected that the E.M.F. of an oxysulphate would 

 differ from that of a corresponding mixture of sulphate and peroxide, 

 and have some definite value ; therefore pastes were made of peroxide 

 of lead, peroxide of lead and sulphate in the proportions of 1 to 1 and 

 1 to 2, and also from the product obtained by treating red lead with 

 dilute sulphuric acid (1 to 5). Experiments made with these pastes 

 showed that there was a difference of degree only between the red 

 lead pastes and the mixtures, and that the lowering of the E.M.F. 

 appeared to depend rather on the intimacy of the mixture, and con- 

 sequent thorough coating of the peroxide granules with sulphate, than 

 on the proportion of sulphate present. 



Mr. Desmond Fitzgerald had already shown, in 1887, afc the Institu- 

 tion of Electrical Engineers, that the mere admixture of lead sulphate 

 with peroxide of lead produces a lowering of the E.M.F. 



With regard to Frankland's observations respecting the colour of 

 the product formed on the peroxide plate during discharge and the 

 reducibility of the sulphate, the author points out that the colour is 

 due to the incomplete reduction of the peroxide, owing probably to 

 the almost complete blocking up by lead sulphate of the pathways by 

 which the current travels through the electrolyte in the paste ; that 

 careful examination of the plugs from a discharged cell shows that 

 the base consists of practically unaltered peroxide of lead, and that the 

 surface, which is rich in PbS04, is really a mass of partially reduced 

 granules of peroxide of lead which' are coated with sulphate. 



Also, though pure lead sulphate is very difficult to reduce, it is very 

 well known that mixtures of lead sulphate and peroxide of lead, or 

 other conducting substances, are reduced with comparative ease, and 

 it is very intimate mixtures of this nature which have to be dealt 

 with as a rule in charging a cell. 



In conclusion, the author points out : 



That neither chemical nor electrical tests give any ground for sup- 

 posing that any other sulphate than the ordinary white PbS0 4 is 

 concerned in the interactions occurring in the cell ; 



That were the sudden lowering of the E.M.F. caused by a change 

 in the nature of the chemical compounds formed on the plates, it is 

 very difficult to account for the very rapid recovery of the E.M.F. 

 exhibited by an apparently discharged cell. 



In the second section tlie electrolyte is dealt with, and, after refer- 

 ring to the work of Berthelot, Richarz, Schone, Traube, and others 

 on the electrolysis of sulphuric acid solutions, the author describes 

 experiments made to test the effect of the addition of sodium sulphate 

 to the electrolyte, as, from information received from Mr. Barber 

 Starkey, it seemed probable that the different behaviour of cells con- 

 taining sodium sulphate was due to the catalytic action of this salt 

 on the hydrogen dioxide always found in electrolysed acid of the 



