38. Note on the Strength of Sulphuric Acid Solution 



used in Secondary Cells in India. 



By E. P. Harrison* 



A very important factor in the maintenance of a second- 

 ary cell is the strength of the dilute acid used to cover the 

 plates. 



The right strength is that which is indicated by experience 

 as giving the best results with the type of cell in question, and 

 is usually made up of 4 parts of acid in 20 parts of water, or 

 20%. Any serious deviation from this strength is sure to short- 

 en the life of the cell and will probably also reduce its output 

 while it lasts. Manufacturers of secondary cells in Europe 

 almost always send out with the ' ' formed ' ' and dry plates 

 instructions as to the density which the dilute sulphuric acid 

 should possess when poured into the cells before charging, 

 while in addition to this they usually supply some form of 

 hydrometer for testing the density of the solution during the 

 various stages of charging and discharging. It is, in fact, well 

 known that careful attention to the density of the solution in 

 the cell is a matter of the first importance. The present Note 

 is intended to draw attention to the fact that a large number 

 of cells charged in India (and probably also in other countries 

 where the average temperature is 30° C. or more) are now, 

 owing to the comparatively high temperature in this country 

 and the consequent reduction in the density of the correct 

 mixture, being filled with solution which contains too high a 



proportion of acid. 



In places where the temperature is 30° C. or over, the de- 

 viation from the correct percentage mixture (which is what 

 really matters) is so considerable as probably to affect seriously 

 the efficiency of the cell. 



Experimental. 



In order to determine quantitatively the errors in the 

 percentage mixture which it is believed are usually made by 

 those who fill cells in India, it was necessary to make two sets 



of measurements: 



(1) Of the variation with temperature of tin- density of 



dilute pure sulphuric acid of some fixed strength. 



(2) Of the change in density of the dilute acid as the per- 

 centage composition changes, keeping the temperature con- 

 stant. 



