168 Messrs. Gladstone and Hibbert 



easily oxidated by means of the current, and is reduced 

 without serious difficulty, especially when broken up by better 

 conducting bodies. 



High Initial Electromotive Force, 



During the prosecution of the experiments described in the 

 preceding pages our attention was again drawn to the high 

 electromotive force which, as is well known, is found in a 

 secondary battery for a short time after the charging current 

 has been stopped. So far as we know, the explanations of 

 this curious phenomenon which have been hitherto given are 

 not looked upon as satisfactory. These explanations depend 

 on the presence and action of electrolytic gases, which are 

 either supposed to be occluded by the electrodes, or else to 

 form secondary products differing from the ordinary elements 

 in much the same way as ozone differs from oxygen. 



We thought it probable that the chief cause of the high 

 E.M.F. might be found in the great inequalities in the strength 

 of acid produced by the charging current. There is no doubt 

 that the acid becomes much stronger in the immediate vicinity 

 of the peroxide plate. The strong and weak acid thus pro- 

 duced at the positive and negative plates respectively, being 

 contained in spongy masses of material, require some time to 

 diffuse, and the normal E.M.F. of 2 volts cannot be attained 

 until diffusion has produced uniformity in the strength of 

 the acid. We put this idea to experimental test. 



Most of the observations were made on a small experimental 

 cell in which were : — 



(1) a negative plate consisting of a strip of lead (1 inch x 3) 

 covered with spongy lead ; 



(2) a positive plate made of similar lead covered with 

 peroxide ; 



(3) an electrolyte of dilute acid containing 18'5 per cent. 

 H 2 S0 4 (=1 volume of acid to about 9 of water). 



We also provided a small porous earthenware jar filled with 

 stronger acid, into which we could introduce the peroxide 

 plate when desired. 



In the first series of experiments the plates were charged 

 in the uniform electrolyte by a current of nearly half an 

 ampere, and after breaking the battery-circuit, observations 

 were taken of the E.M.F. by the condenser method. 



