ELECTRICAL ARC. 693 



a fall of potential of 50 volts ; the electrical work per second is 



U = 5 XI5 = 76-45 kgm., 

 9 'oi 



or i '02 horse-power. The arc light is thus six times as powerful 

 as the incandescent lamp, for the same expense. 



1249. ACCUMULATORS. When two electrodes, one of which is 

 polarized, are connected by a conductor, the secondary current (253), 

 or rather the discharge of the polarization, is usually rather weak, 

 unless the polarization is kept up by an extraneous cause, as in 

 -Grove's gas battery, in which two platinum plates, which act as 

 electrodes, are respectively immersed in oxygen and in hydrogen. 



Nevertheless, with certain metals (1081) the capacity of polarisa- 

 tion may become considerable, because the reactions, instead of 

 being confined to a thin surface layer, penetrate into the interior 

 of the electrode, and thus put in" play an important weight of matter. 



M. G. Plante* has investigated most of the metals from this point 

 of view, and has shown that a quantity of electricity, and therefore 

 a considerable quantity of energy, may be stored in such a secondary 

 battery. For some years these secondary couples have been called 

 accumulators of electricity. 



The best arrangement, according to M. Plantej is to immerse two 

 plates of lead parallel and very close to each other in dilute sulphuric 

 acid. The maximum electromotive force is higher than 2 volts. A 

 remarkable property, also observed by M. Plante,f is that the capacity 

 of polarization increases in proportion as the accumulator is formed 

 that is to say, according to the number of times it is charged and 

 discharged, so that the oxidizing action of the primary current 

 penetrates more deeply, the galvanic deposits thus formed being 

 exceptionally porous. The formation of these couples is greatly 

 accelerated by covering the lead plates, or filling the cavities they 

 contain with a layer of red lead. This idea seems to have been due 

 to M. Faure ; \ but in practice it is difficult to make the metal 

 arising from the reduced oxide adhere to the lead plates. 



M. Plante has observed that the electrochemical formation of 

 the couples is accelerated by a rise of temperature, but he attains 



* G. PLANT. Recherches sur r Electricite. Paris, 1879. 

 f G. PLANTE. Comptes rcndus, Vol. LXXIV., p. 592. 1872. 

 J E. REYXIER. Comptes rendus, Vol. xcii., p. 951. 1881. 

 G. PLAXTE. Comptes rendus, Vol. xcv., p. 418. 



