Dr. J. Henderson on Cadmium Standard Cells. 155 



It will also be noticed that the values obtained for Set I. 

 are practically identical with those obtained for Set IT., -which 

 indicates one very important advantage which these cells 

 possess, namely that it is a matter of indifference whether 

 neutral or acid salts are employed in their construction, pro- 

 vided acid is not added. 



Temper at u re- Coefficient. 

 The temperature-coefficient of the cells was calculated from 

 the results of the E.M.F. observations at different tempera- 

 tures, and the mean value obtained for Set I., exclusive of the 

 cell with added acid, was '005 per cent, per l c C, the maximum 

 being *001> per cent, and the minimum value *002 per cent. 

 For Set II., exclusive of the acid cell, the mean value was 

 *003 per cent, per 1° C, the maximum being '004 per cent, 

 and the minimum "002 per cent. The coefficient for the acid 

 cells was larger in both cases, being "007 per cent, for the 

 Set I. cell, and "006 per cent, for the Set II. cell, thus showing- 

 very clearly one effect of added acid. 



Time-Lag. 



In all the cells the experiments had pointed to the existence 

 of a considerable lag of the E.M.F. behind the temperature- 

 change ; and in order to get some idea of the amount of this 

 lag, cells from each set were kept for some hours at a con- 

 stant temperature and then placed in a water-bath at a 

 considerably higher temperature; the E.M.F. was measured 

 at stated intervals until it became constant. In all cases the 

 E.M.F. showed a sudden drop on first heating, the amount 

 increasing with the acidity of the cell, and being about 

 *2 per cent, for cells in Set II. when the temperature was 

 suddenly changed from llt° O. to 30° C. After the first drop 

 the value rose slowly until after about two hours it became 

 constant. 



Recovery from Polarization. 



Very satisfactory results were obtained from these cells 

 with respect to the recovery of E.M.F. after polarization. 

 The E.M.F. of a cell connected in series with a 1000-ohm 

 coil for five minutes was found to have completely returned 

 to its original value 2 minutes after the circuit was broken. 

 Several cells were then short-circuited with thick copper 

 wires for 5 minutes, and 5 minutes after the circuits were 

 broken they had returned to within 04 per cent, of their 

 former value, whilst after 10 minutes they had come within 

 02 per cent, of their original E.M.F. If the cells were 

 given a slight charge for about 1 minute from an E.M.F. 



