IB^ 



Discharge 

 PbO, 4- Pb + H, SO, :^ 2 PbSO, + 2 H,0. 

 Charge 

 By reference to tliis equation it is now possible to calculate a priori 

 the influence of pressure on the E. M. F, of accumulators of this kind. 

 This influence has been determined experimentally in the van 't Hoff- 

 Laboratory by Dr. G. Timofejrw, who will shortly publish his results. 

 The connexion between the influence of pressure on the E. M. F. 

 of a reversible galvanic cell (such as the accumulator is) and the 

 changes of volume which occur when the quantity of electricity de 

 passes through it, are given by the equation ') 



/dE\ _ fdv\ 



\dp Jt.v \d8 jT.p ' 



where E is the E. M. F. of the cell at the pressure p and dv 



the change of volume mentioned. 



This change can be calculated if the spec, volume of the systems 



which are present before and after the passage of the quantity of 



electricity ds are known, but it can also be determined experimentally. 

 While Dr. Timofejkw followed the first plan, we have employed 



the second. A full description of our experiments will be published 



before long in the Zeitschrift fiir 

 physikalische Chemie. 



Two plates of pure lead (3 cm. 

 broad, 10 cm. long and 5 mm. thick) 

 were perforated as shown in the 

 diagram B. These were placed in a 

 glass-dilatometer (of approximately 

 150 cc. content) and fixed with com- 

 pound-glue in the holes CC. The 

 upperends of the plates were fastened 

 in a piece of ebonite in order to 

 avoid any contact. The glass cover 

 D was held in its place by means 

 of two spiral springs. The apparatus 

 was filled with diluted sulphuric acid 

 through the funnel GB. The fluid 

 was pressed into the horizontal part 

 of a capillary tube EF by means 

 of an india-rubber bulb. The stop- 

 cock H was then closed. The capil- 

 lary tube was placed on a milli- 

 1) Ernst Cohen and L. R. Sinnige, Zeitschr. fiii- physik. Chem. 67, I (1909). 



