Chap. 10] 



ELECTRICAL METHODS 



639 



Contrary to metals, the conductivity of electrolytes increases with an 

 increase in temperature, so that 



<re = «Ti8[l + 5(e - 18° C.)]. 



(10-8) 



Qeslstivify 



Ohmm 



While in metals the temperature coefficient of resistivity is the reciprocal 

 of the absolute temperature, the temperature coefficient of electrolytes 

 (being the increase in ion mobility due to a reduction in the viscosity of 

 the solvent) is approximately equal to the temperature coefficient of 

 viscosity of water. For NaCl solutions the coefficient is 0.022; for an 

 increase in temperature of 35° C. the conductivity is about doubled (see 

 Fig. 10-4). 



Metals and electro- 

 lytes also show a 

 difference in alternat- 

 ing current conduc- 

 tion. In electrolytic 

 solutions voltage and 

 current are generally 

 not in phase, particu- 

 larly when the polari- 

 zation e.m.f. is com- 

 parable with the 

 applied e.m.f. The 

 phase shift is reduced 

 as the voltage is in- 

 creased. If P is a 

 "polarization con- 

 stant" (ratio of polar- 

 ization e.m.f. and quantity of electrolysis products deposited per unit 

 surface of electrode), the impedance of an electrolytic solution is 



Temperature 



icr?(rxf4(r5(r6(f7irdcr9(fiocrc 



Fig. 10-4. Decrease of resistivity of an NaCl solution 

 with temperature (after Sundberg). 



Z = K4/l-h 



/■ 





Substituting 1/Cp for P, eq. (10-9a) takes the form 



Z = 4r Vl + 0)2 Cp 2^2, 



(10-9a) 



(10-96) 



which is seen to be identical with the formula for the impedance of a 

 circuit consisting of a resistance wdth a capacity in series. The phase 



' See oscillograms in W. R. Cooper, Electrolysis as Applied to Engineering, p. 16 

 (New York, 1923). 



