44 Experiments on the Faure Accumulator. 



resuscitating-power is wonderfully marked. An insulation of 

 a few hours will cause the energy given off per minute on 

 redischarging to be eight to ten times as great as it was before 

 insulation. Indeed on one occasion, after a cell had apparently 

 nearly discharged itself, it was left shortcircuited with a thick 

 wire for half an hour, then insulated all night, when the num- 

 ber of foot-pounds of work per minute given off at the com- 

 mencement of the discharge the following morning was found 

 to be ten times as great as it was on the previous evening, and 

 a greater amount of energy was actually taken from it in the 

 second discharge than in the first. This phenomenon gives 

 the Faure accumulators a great value for tramcar propul- 

 sion, since, as is well known, it is just on starting after stop- 

 ping that the strain on the horses is so great. 



Efficiency. — To determine the efficiency of cells we com- 

 mence with them empty, or at least as empty as many hours' 

 shortcircuiting with a thick wire could make them. We 

 then measured the total amount of energy put in and the 

 total amount subsequently given out, and we found that, for 

 charges up to a million foot-pounds put into the cell and dis- 

 charged with an average current of 17 amperes, the loss in 

 charging and discharging combined may not exceed 18 per 

 cent. Indeed, for very slow discharges the loss in charging 

 and discharging combined in some of our experiments has been 

 as low as 10 per cent. 



Storing-power. — It is a little difficult to measure the maxi- 

 mum storing-capacity of the cell at the same time that mea- 

 surements are made of its efficiency, because in the latter case 

 we must take care that we do not put in more electric energy 

 than the cell can hold ; on the other hand, if precautions are 

 taken to avoid overcharging, it is a little difficult to ensure that 

 the full charge has been put in. We have therefore separated 

 our experiments for measuring the efficiency from those em- 

 ployed to ascertain the storing-power. 



Let us take a single example of the storing-capacity. A 

 certain cell containing 81 lb. of lead and red lead was charged 

 and then discharged, the discharge lasting eighteen hours — 

 six hours on three successive days; and it was found that the 

 total discharge represented an amount of electric energy ex- 

 ceeding 1,440,000 foot-pounds of work. This is equivalent to 

 one horse-power for three quarters of an hour, or 18,000 foot- 

 pounds of work stored per pound weight of lead and red lead. 

 The curve shows graphically the results of the discharge. 



Horizontal distances represent time in minutes, and vertical 

 distances foot-pounds per minute of energy given out by the 

 cell, and the area of the curve therefore the total work given 



