164 Messrs. Gladstone and Hibbert 



longer obtained when the sodium-sulphate solution contained 

 sulphuric acid in the proportion of 1 volume to 10. The acid 

 present interferes with such a simple test, and we sought for 

 information on the point by determining the ratio of acid to 

 sulphate of soda in the pores of the spongy lead, and com- 

 paring it with the ratio of the same substances in the body of 

 the liquid. Preliminary experiments indicated the following 

 as the best course to pursue. 



A strip of spongy lead was used as cathode in a liquid 

 somewhat similar to that analysed above. The ratio was 



TT ^/-\ 



2 * =30. A current was passed for three hours, falling 



JMagov^ 



slowly from about 2 amperes to 1*5. The strip was then taken 

 out and placed in 120 cubic centim. of distilled water and 

 allowed to diffuse for 40 minutes. It was then placed in 

 fresh distilled water for 18 hours. The forty minutes' diffu- 



sate gave a ratio of ~J~ 2 ^ n 4 =25, only a little lower than that 



shown by the original liquid. The 18 hours diffusate gave 



a ratio AT 2 Qr f =11*8. Evidently, then, the portions of the 



JNa2^^4 

 liquid which diffused last were much richer in sodium salt 

 than the earlier ones. 



This would show that a large proportion of sulphate of 

 sodium is formed in close contact with the lead sulphate, and 

 we have already seen that this is favourable to the reduction 

 of that body. 



But there is another consideration. It is well known that 

 the spongy lead formed on one of the plates in a secondary 

 battery is to some extent acted on by the liquid. 



It occurred to us that this direct chemical action between 

 lead and sulphuric acid might be influenced by sodium sul- 

 phate. We therefore placed a quantity of red lead on a sheet 

 of lead and reduced it electrolytically. The sheet was then 

 cut into small pieces and divided into two equal quantities 

 of about 20 grammes each. One half was put into a flask 

 containing 1 volume of acid to 6 of water ; the other half 

 was put into a similar acid with the addition of 5 per cent, 

 of sodium sulphate. Hydrogen gas was evolved from both 

 flasks at the ordinary temperature. The following Table 

 shows the results : — 



