192 ELECTRICAL RESISTANCE OF ACETIC ACID 



THE OBJECTS OF THIS WORK WERE: 



1. To determine a satisfactory method for the meas- 

 urement of large electrolytic resistances. 



2. To measure the electrical resistance of acetic acid in 

 the solid and liquid phases at different temperatures and to 

 find the causes of the variations which occur. 



3. To determine the effect of small quantities of water 

 on the resistance. 



In the measurement of electrolytic resistances the effects 

 of the electro-motive force of polarization are in general quite 

 marked. This polarizing effect consists of two parts; one of 

 which is a function of the current, f(i), and is in fact, a 

 variable resistance, increasing with time due to the deposition 

 of gas on the electrodes. The other part, e, is a true polariz- 

 ation e. m. f. which is independent of the value of the current 

 passing thru the electrolytic cell. It seldom amounts to more 

 than 1 or 2 volts. Any alternating current method should 

 practically eliminate both of these effects. 



Using the well known method of Kohlrausch, resistances 

 greater than 10 5 ohms, cannot be measured with any great 

 accuracy. For satisfactory measurements of resistances 

 ranging between 10 4 and 10 8 ohms another alternating current 

 "bridge" method is suitable. In this method the telephone 

 or galvanometer of the Kohlrausch apparatus is replaced by 

 an electrometer and two of the resistances by capacities. 



To measure resistances greater than 10 8 ohms, a direct 

 current method may be used. The f(i) term of the polariz- 

 ation effect will be very small as compared with the total resis- 

 tance because the current flowing thru the cell will be minute, 

 and furthermore as the applied e. m. f. is large the "f" term 

 will be a small fraction of the total e. m. f. Using a sensitive 

 galvanometer, connected as in figure 1, resistances ranging 

 from 10 8 to 10 10 ohms may be conveniently measured. 



