" THE ELECTRIC STORAGE OF ENERGY:' 547 



From the ease with which secondary batteries can be constructed 

 of very low resistance, so that they will give for a short time what 

 practical electricians call a quantity current, they have been for some 

 time in use for certain special purposes, principally for heating the 

 wire of the galvanic ecraseur in surgical practice. By a secondary 

 battery is meant a galvanic battery which, as at first put together, has 

 no tendency to give a current at all ; but, if a current of electricity be 

 passed through it of sufficient tension to decompose the fluids which it 

 contains, will give a current in the opposite direction, due to the recom- 

 bination of the separated parts of the decomposed fluid. The older 

 forms consisted of two plates of platinum, preferably coated with 

 spongy platinum immersed in a weak mixture of sulphuric acid and 

 water, the action in this case being that the charging current decom- 

 poses the water (either directly or as the result of a chemical action 

 set up by decomposing the acid first) into oxygen and hydrogen, which 

 gases are absorbed by the platinum plates, the oxygen by one and the 

 hydrogen by the other. When the charging battery is removed, the 

 secondary battery will give a powerful current until all the oxygen 

 and hydrogen absorbed by the plates are recombined in the form of 

 water. It was afterward found that satisfactory results could be got 

 from plates of lead treated in the same way. Their employment, of 

 course, redwced the first cost of the apparatus. M. Plante then pro- 

 duced his secondary battery, in which he obtained great surface, and 

 consequently low internal resistance, and large current, by rolling into 

 a spiral form two lead plates separated by pieces of insulating material 

 placed between them at intervals. He further succeeded in greatly 

 increasing the time for which the battery would yield a given current, 

 or its capacity, by adopting an elaborate process for the " formation " 

 of the plates, which consisted in charging the battery and discharging 

 it, varying the direction of the exciting current, and leaving the bat- 

 tery undisturbed between the charging and discharging for gradually 

 increasing intervals of time. This process added enormously to the 

 expense of the apparatus, which was also too bulky and heavy. 



M. Faure, however, has succeeded in increasing the capacity of the 

 battery, and getting rid of the long and delicate process of formation. 

 His battery, like M. Plante's, consists of two plates of lead rolled 

 together into a spiral, but he coats each plate with a thin layer of red- 

 lead (one of the oxides of that metal), kept in its place by a piece of 

 absorbent felt, which also keeps the two plates from touching. This 

 felt is saturated with the weak acid. The effect of the exciting cur- 

 rent in this case is to deposit spongy lead on one plate and to convert 

 the red oxide on the other into puce-colored oxide which contains more 

 oxygen than the red form ; no doubt, also, the spongy lead at a late 

 period of the charging becomes saturated with hydrogen. When the 

 battery is now set in action, the spongy lead becomes reoxidized to red- 

 lead and the puce-colored oxide reduced to the same salt. 



