'80 



REPORT — 1898. 



The means of the results of experiments 13-49 inclusive, which do not differ 

 much from the above, are also given. 



The mean capacity and efficiencies from tests 6 and 7 of the second series of 

 constant P.D. tests are also given, and it will be noticed that the energy 

 efficiency is somewhat less than in Mrst series. 



The density of the acid varied from 1-159-1'175 in the first series of tests and 

 from l'164-l474 in the second series of tests. 



' Gassing,' or the brisk evolution of hydrogen bubbles from the negative plates, 

 occurred just after the first rapid fall of current was over ; this was when about 

 two-thirds of the charging time had elapsed. 



Hesistance. — Only approximate figures can be given, as no special arrangements 

 were made for taking the E.M.F, accurately at the moment of making or breaking 

 the circuit. 



During the last few tests of the second series the resistances were as below : — 



Beginning of charge 

 00033 ohm. 



End of charge Beginning of discharge End of discharge 

 0-01 ohm. 00043 ohm. 0-0033 ohm. 



Skajje of Curves. 



Charging. — At the beginning of the charge the currents are, of course, very 

 large, about 170 amperes being the usual initial current. 



During the first three minutes of the charge a curious phenomenon always took 

 place. The current fell by about 10 or 20 amperes, and then rose again very 

 rapidly. After remaining fairly constant for about three minutes, the current falls 

 very rapidly to about 40 amperes, and then drops much more gradually, becoming 

 nearly constant at 10 amperes at the end of the charge. 



This initial falling and rising again of the current we considered to be due to 

 an excessive liberation of hydrogen by the large currents, causing a temporary 

 increase in the back E.M.F. of the cell. 



It did not occur in the first few experiments of the second series of tests at 

 constant P.D., but appeared to a lesser extent in the last. The curves in these 

 tests showed a steady falling oil' of current throughout. 



Discharijing. — The P.D. shows a very rapid initial drop, after which the curve 

 bends off nearly at right angles, and then keeps quite level for a considerable time. 

 After this the P.D. falls at an increasingly rapid rate. After a charge at constant 

 current, the P.D. falls rapidly at first, and the change to the nearly level portion 

 is not abrupt. 



In the first case — i.e. after a constant P.D. charge — the rapid fall is practically 

 over in the first three minutes, and after this the curve is nearly level ; whereas in 

 the other case the initial drop lasts three or four times as long, and the curve after- 

 wards shows a gradual fall. 



Charging at Constant Current. 



By this method we obtained considerably smaller capacities, but higher 

 efficiencies. 



The working efficiency was obtained from the results given by experiments 44 

 and 45. 



