Popular Science Monthly 



793 



A New Method of Reviving Old 

 Dry Batteries 



N( >\V that all sorts of electric pocket 

 llashiights and electric lanterns are 

 common, it is worth while to know that 

 the batteries for them need not be 

 thrown away immediately after the 

 light loses its original brilliancy. When 



Three partly exhausted cells are connected, 

 two in series and the third across terminals 



a dry cell is so far exhausted tliat it 

 produces nothing more than a quickK- 

 fading glimmer of light, which it would 

 t)rdinarily keep at full brilliance, it is 

 usually discarded as worthless. Such 

 batteries may, however, be set aside 

 until a number of them have accumu- 

 lated; and some of them may be used to 

 revive the others by the following 

 method, which is applicable to the dry 

 battery because it possesses, to a certain 

 degree, the jiropcriy of reversibility. 



When three partly exhausted cells 

 have been accumulated, connect two of 

 them in series, and the third one across 

 their terminals in reverse series, as 

 shown in the drawing. When this is 

 done, it will be seen that the electro- 

 motive force of cells A will more than 

 balance that of cell B; and a small 

 current will tlow through the entire 

 battery, passing through cell B in the 

 reverse direction from normal. The 

 reversed cell, therefore, becomes vir- 

 tually a storage cell, and slowly takes on 

 a charge from the other batteries. 

 After being left in this position for a 

 few da\s, cell B may be disconnected 

 and again used in the regular wa>'. .\ 



cell thus reviveil will be as good as new. 



M<ire than three cells may be con- 

 nected ; for example, three cells A , 

 may be set to reviving two cells B; in 

 which case the action will be slower 

 because the electromotive force of the 

 odd cell, A, must overcome the internal 

 resistance of five cells instead of three, 

 as in the first case. 



Old dry cells for any other purpose 

 may be revived in the same way. They 

 may be tested for exhaustion by con- 

 necting them to an ammeter or to some 

 piece of apparatus such as a bell or 

 telegraph-sounder, and comparing the 

 effect produced by one of the old cells 

 with that produced by a fresh cell when 

 connected to the same. As an ammeter 

 |:)Uts a cell on practically a short circuit, 

 it should be used quickly to avoid 

 further exhaustion of the strength of the 

 cell. The property of reversibility is 

 not possessed by all types of primary 

 Ijatteries; and it must be borne in 

 mind that this article has reference only 

 to the dry cell. — Edwix C. Wright. 



A Home-Made Fuse for a Small 

 Battery Current 



THE beginner in electrical science 

 who wishes to demonstrate the 

 action of a fuse on a small scale will find 

 the following a suitable form to use. 

 Make a little wood block .1, 2 in. long 

 by 1 3-2 in- wide, and fix two brass 

 springs, B, one at either end. The 

 screws used to secure these also serve 

 for the attaghment for connecting wires.' 

 Take a i-in. length of glass tube, C, 

 and cork both ends, pasting a very 



Home-made 

 fuse for battery 

 circuits 



narrow strip of tinfoil D — y^ in. or less — 

 along the side and covering both corks 

 with a wider piece of foil. The tube 

 can then be gripped between the springs. 

 This forms a good fuse for small currents. 



