TEMPERATURE COEFFICIENT <)F ICE.— JOHNSTONE 185 



3)latiiiuni wires, d and d^ sealed in the end as shown in the 

 ^figure. Thes3 four tnbes are fitted carefully in corks, and 

 then in the '"'U" tube as shown. 



Xow suppose we fill the tube with an electrolyte and pass 

 a current through it, by way of the electrodes b and ^i- There 

 will result a polarization at these electrodes and the value of 

 the current will vary somewhat with the time. If this current 

 is measured by a sensitive galvanometer and if the dift'erence 

 in potential of the two electrodes is measured by a voltmeter, 

 a value of the resistance of the electrolyte could be calculated 

 ;at any particular time; but this is a varying quantity, and not 

 the true resistance of the electrolyte. 



ISTow if two other electrodes a and a (see Fig. 5), are placed 

 in the position sho\\Ti in the figure, their ends c and c^ being 

 lower somewhat than the extremities of the platinum wires 

 d and di, and then a current is passed through the electrolyte 

 hy way of the electrodes d and d{, then if we measured the dif- 

 ference of potential between the points c and C], by some electro- 

 static instrument and knew the value of current, we could' 

 calculate the value of the resistance of the electrolyte between 

 the points c and c,, and the resistance so calculated would be 

 constant in value and unaffected by polarization. This would 

 be so, because when there is a variation in the current due to 

 polarization or any other causes, there will be a proportional 

 ■change in the potential difference between the two potential 

 electrodes, so that the ratio of the potential difference to the 

 ■current will be constant (with a const, temp.). Therefore the 

 resistance determined in this way will have a constant value. 

 Thus, polarization effects will be eliminated. 



The current passing through the electrolyte, (which was 

 ice in this case), w^as measured by a Dolezcdeh electrometer, 

 A, (see Fig. 5). The potential of each potential electrode 

 ivas measured by a Wilson Tilting electroscope, D, the plate 

 of the electroscope being kept at a potential of 320 volts, from 

 small storage cells. A calibration curve for this instrument, 

 -as it was used in these experiments is shown in Fig. 6. It 



