1889.] 



the Chemistry of Storage Batteries. 



305 



at any time be measured by ascertaining the amount of free sulphuric 

 acid in the cell ; in other words, by simply determining the specific 

 gravity of the electrolyte ; and this method has since been very 

 generally adopted by the users of storage batteries. 



In continuing these experiment's, it soon became evident that the 

 lead sulphate formed and decomposed in the cell could not be the 

 ordinary white sulphate hitherto known to chemists, becfiuse, in the 

 first place, the active material of the plates always remains coloured 

 even after discharge, and secondly, because whenever white sulphate 

 is produced through abnormal reactions in the cell, it is afterwards 

 decomposed only with extreme difficulty by the electric current. 



In order to obtain some light upon the composition of the sulphate 

 formed and decomposed in the cell, I have studied the action of 

 dilute sulphuric acid upon litharge and minium, the two oxides of 

 lead chiefly used in the construction of the plates of storage cells. 



Action of Dilute Sulphuric Acid on Litharge. 



Finely powdered litharge was treated with successive portions of 

 dilute sulphuric acid until the liquid remained strongly acid after 

 prolonged trituration. The resulting insoluble buif-coloured powder 

 was washed with water till free from acid, and dried, first at 100° C. 

 and afterwards at 150 — 160°. The loss at this higher temperature 

 was less than 0'2 per cent., and was therefore due to hygroscopic 

 moisture. 



PbO and S0 3 were then determined in the dried compound as 

 follows : — The salt was dissolved in a small quantity of pure con- 

 centrated solution of caustic potash, and the solution, after dilution, 

 was saturated with C0 2 . (According to H. Rose, COPbo" is soluble 

 in COKo 2 , but not in COHoKo.) Any excess of C0 2 , which might 

 have caused the COPbo" to dissolve, was avoided by warming the 

 liquid with the precipitate on the water-bath to a temperature at 

 which the COHoKo begins to dissociate. The liquid was then 

 allowed to cool and to stand twelve hours before filtering. The 

 COPbo" was filtered off, converted into nitrate, and precipitated and 

 weighed as sulphate. The sulphuric acid was determined in the 

 filtrate from the COPbo". 



1*2964 grams of the salt gave 0'6647 gram baric sulphate and 

 1*4437 gram plumbic sulphate. 



These numbers agree closely with the formula — 



(S0 3 ) 3 (PbO) 5 , 



as is seen from the following comparison of calculated and experi- 

 mental numbers : — 



z 2 



