474 Journal of the Asiatic Society of Bengal. [September, 1910.] 



1st. Read off on curve 2 the density corresponding to a 

 20% mixture: this is seen to be 1,187, and the temperature 

 corresponding is 25-2°C. 



2nd. Set up on curve 1 at a temperature of 25-2° an 

 ordinate AB of value 1,187. Through B draw a curve (prac- 

 tically a straight line) parallel to the original 22-2% curve XX. 

 This new curve will represent the variation with temperature 

 of the correct 20% mixture. Reading off from the curve YY 

 Fig. 1 the density corresponding to a temperature of 30°C, 

 we obtain 1,183. 



Now, in India, with cells at the assumed temperature of 

 30°C. the practice is to use acid solution of density 1,190. 



A density of 1,190 at 30°C. is, however, equivalent to a 

 density of 1,1935 at 25-2° (Fig. 1.), and from Fig. 2 this is seen 

 to correspond with a composition of 22-8%. 



Finally then, a density of 1,190 at 30° corresponds with a 

 composition of 22-8%, whereas the correct mixture on which 

 the welfare of the cell depends should contain 20% of acid : a 

 difference of 3%. Now consider the automatic changes which 

 go on in the density of the solution during the process of 

 charging. The total change in solution-density in Europe due to 

 chemical action is from 1,190 before charging, to 1,220 after 

 charging, which is an increase of about 6% in the solution- 

 strength. Thus by using solution made up to a density of 1,190 

 in India at 30°C. we are filling the cells with a mixture which is 

 too rich in acid, the error being as much as half the total den- 

 sity change in the cell due to chemical action. 



It is clear from the above reasoning that the solution 

 density which ought to be employed for filling secondaries at a 

 temperature of 30°C. (in so far as changes in temperature 

 affeot density alone) is about 1,183, a number which is read off 

 directly from curve YY, Fig. 1. 



Further experiments on the output of different cells 

 filled with acid solution of the same density but kept at differ- 

 ent temperatures would be interesting. The effect of wrong 

 solution-strength on the life of a cell would obviously be more 

 difficult to determine since the life depends on so many factors 

 which it is hard to fix. In conclusion , my thanks are due to 

 Babu Rabati Raman Dutt, M.A., Government Research Scholar 

 of Presidency College , by whom nearly all the actual experi- 

 mental measurements described in this Note were made. 



