ELECTROLYSIS. POLARIZATION. CONSTANT BATTERIES. 643 



ELECTROLYSIS. TRANSITION-RESISTANCE. GALVANIC POLARIZATION. 



CONSTANT BATTERIES AND UNPOLARIZABLE ELECTRODES. 



INTERNAL POLARIZATION OF MOIST CONDUCTORS. 



CATAPHORIC ACTION OF THE GALVANIC 



CURRENT. SECONDARY RESISTANCE. 



Every galvanic current that is passed through a fluid conductor causes de- 

 composition of the fluid {electrolysis). The products of decomposition, designated 

 ions, are deposited at the poles immersed in the fluid, the electrodes (of which the 

 positive is designated the anode and the negative the kathode} , anions collecting 

 at the anode and kations at the kathode. If the products of decomposition are 

 deposited upon the electrodes, they may mechanically, through their adhesion, 

 either increase or diminish the difficulty of conduction through the electric fluid. 

 This is designated transition-resistance. If by this means the conduction-resistance 

 already present in the battery is increased, the transitional resistance is designated 

 positive, while if it diminishes the conduction-resistance in the battery, it is desig- 

 nated negative transition-resistance. 



The ions that collect at the electrodes may, however, modify the strength of 

 the current also by the development between the anions and the kations (as 

 between two different bodies connected by a conducting fluid) of a new galvanic 

 current. This phenomenon is designated galvanic polarization. Thus, for ex- 

 ample, water is decomposed by immersed platinum electrodes in such a manner 

 that the negative oxygen collects at the positive pole, and the positive hydrogen 

 at the negative pole. The polarization-current thus generated usually has a 

 direction opposite to that of the original current, and, accordingly, is designated 

 negative polarization. In rare cases, however, the polarization-current has the 

 same direction as that induced by the decomposition and then the phenomenon 

 is known as positive polarization. 



Naturally, in the process of electrolysis both factors may be operative, 

 namely transition-resistance, as well as polarization. 



Polarization, when present, may be so slight as not to be recognizable with 

 the naked eye, but it may then be demonstrated in the following manner: After 

 the lapse of a short time the primary source of the current, for example the element 

 with which the electrodes were connected, is excluded, and the extremities of 

 the electrodes projecting out of the fluid are placed in communication with a 

 multiplicator, which at once indicates even slight polarization by deflection of the 

 needle. 



The ions set free in the process of electrolysis cause, at times, at the moment 

 of their development, further secondary decomposition. If, for example, platinum 

 electrodes are immersed in sodium-cmorid solution, chlorin accumulates at the 

 anode, and sodium at the kathode. The chlorin, however, immediately exerts a 

 decomposing influence upon the water, the oxygen of which it takes up for oxida- 

 tion, while the hydrogen is deposited secondarily at the kathode. 



The degree of polarization increases (although in slighter measure) with 

 the current-strength, while it diminishes almost proportionately with elevation 

 of temperature. The endeavor to overcome the polarization, which, as can be 

 seen, would soon modify the strength of the galvanic current present, has led 

 to the invention of two important devices, namely, constant galvanic batteries and 

 the so-called unpolarizable electrodes. 



The constant batteries yield a constant current, that is a current of the same 

 intensity, because the ions generated upon the electrodes are removed at the 

 moment of their development, so that they are thus unable to give rise to a polari- 

 zation-current. For this purpose the two bodies used for the tension-series are 

 each immersed in a separate fluid, separated by a porous septum (porcelain 

 cylinder). In the zinc-platinum cell of Grove the zinc is immersed in dilute 

 sulphuric acid, the platinum in nitric acid. The oxygen deposited in the process 

 of electrolysis at the positive zinc forms zinc oxid, which is at once dissolved in 

 the dilute sulphuric acid. The hydrogen attracted to the platinum unites at once 

 with the nitric acid to form water, the acid giving off oxygen and being converted 

 into nitrous acid. The zinc-carbon cell of Bunsen acts in the same way, the nega- 

 tive carbon being immersed in nitric acid, the positive zinc in dilute sulphuric 

 acid. In the cell of Daniell the positive zinc is immersed in dilute sulphuric 

 acid and the negative copper in a concentrated solution of copper sulphate. The 

 zinc undergoes the same change as in the Grove cell. The negative copper, how- 



