A manual of practical medical electricity : the Röntgen rays and Finsen light . lanche Cell. The Leclanche cell is of far more importance (Fig. 14). (a) The electrolyte is a strong solution of ammoniumchloride, which half fills a glass jar. (b) The positive element is a rod of amalgamatedzinc. (c) The negative element is formed of a rod of carbonsurrounded by coarsely-powdered carbon and peroxide ofmanganese, all enclosed in a porous pot which stands inthe glass jar. (d) The depolarizer is the manganese peroxide. The electro-motive force (E. M. F.) is about i47 volts,and the internal resistanc
A manual of practical medical electricity : the Röntgen rays and Finsen light . lanche Cell. The Leclanche cell is of far more importance (Fig. 14). (a) The electrolyte is a strong solution of ammoniumchloride, which half fills a glass jar. (b) The positive element is a rod of amalgamatedzinc. (c) The negative element is formed of a rod of carbonsurrounded by coarsely-powdered carbon and peroxide ofmanganese, all enclosed in a porous pot which stands inthe glass jar. (d) The depolarizer is the manganese peroxide. The electro-motive force (E. M. F.) is about i47 volts,and the internal resistance of the cells varies from aboutone to five ohms. > During^action the ammonium chloride attacks the zinc 3 34 A Manual of Practical Medical Electricity to form zinc chloride, ammonia and hydrogen being set free. Zn + 2NH4CI = ZnCl2 + 2NH3 + Hg. The ammonia dissolves in the water (one volume ofwater can absorb more than 700 volumes of ammonia atthe ordinary temperature) until it is saturated, when thegas escapes. The hydrogen appearing at the negative element unites ^S3*=^. Fig. 14.—Leclanche Cell. with some of the oxygen of the manganese peroxide toform water, the peroxide being reduced to the sesquioxide. H2 4-2Mn02 = H2O + MnA- The manganese peroxide thus acts as the depolarizer,the cell becoming inefficient when it is all , as the resulting sesquioxide is a poor conductorof electricity, and as there is a tendency to the formationof double salts which crystallize on the zinc, the internalresistance gradually increases, and the chemical action Forms of Primary Cells 35 diminishes, even if we leave the weakening of the am-monium chloride solution due to its decomposition out ofaccount. A peculiarity of this cell is the rapidity with whichit becomes temporarily polarized when short-circuited—that is, when its poles are put into metallic connectionwith only a low external resistance. The manganeseseems to be unable to depolarize sufficiently rapidly tokeep
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