TEMPERATURE COEFFICIENT OF ICE, JOHNSTONE. 133 



As resistances calculated from such values of the current as 

 the above would have little or no value, a method was then 

 sought, whereby the effects just indicated could be eliminated. 



A great deal of time was spent in attempting to find out 

 the nature of this polarization and measure its value. The 

 "Tuning Fork"^ method of measuring electrolytic polarization 

 was used first of all, with water as the electrolyte, and correct 

 values were obtained. But when the ice cell was substituted 

 for the water cell, this method would give no results on account, 

 principally, of capacity effects. A "'commutator" method was 

 also tried with similar results. 



By using Ivohlrausch's method for measuring the resistance 

 of electrolytes, the - polarization effect would probably be 

 eliminated. However, the maximum resistance that can be 

 measured by this method is of the order of 10^ ohms. As ice 

 has a specific resistance of more than 10^ ohms', this method is 

 not practicable. It might be possible however, by taking thin 

 sections of a block of ice, to measure its resistance by means 

 of ISTernst's conductivity apparatus.^ 



jSTow one of the methods of measuring the resistance of a 

 solid conductor, is to determine the drop in potential between 

 two sections of the substance, when a steady current is flowing 

 through these sections. Knowing the values of i and e, the 

 resistance can be calculated. 



A method very similar to the above was adopted, and as 

 will be shown, the effects of polarization, etc., will be elimi- 

 nated as far as the measurement of the resistance is concerned. 



The apparatus was set up, as shown in Fig. 5. B, is a "U" 

 tube, 12 cm. in height, with a bore of about 2 cm. a and ci^ are 

 glass tubes of 2|- mm. bore, with platinum points sealed at the 

 ends c and Cy h and h j are slass tubes of 4 or 5 mm. bore, with 



1 Watson, M. :— Text book of Physics, page 790. 



■> Nernst, W. :— Zeitschr. f. phvs. Cheni., 14,- 622, (1894) ; also Maltby, M. E. : 

 ibid. 18, 133, (1895). 



