IN THE SOLID AND LIQUID PHASES.— JOHNSTONE. 201 



It was found that the specific resistance of the samples 

 used, changed considerabh' with time and according to the 

 previous history of the tube. This is to be expected, because, 

 the action of the acid on the glass tube will result in the 

 addition of impurities, which will continually decrease the 

 value of such a high resistance as is being dealt with. 



The change in resistance of the solid acid with change in 

 temperature is evidently not a true temperature coefficient. 

 It is due in a large part to three factors which are functions of 

 the temperature. 



There exists in the tube what may be regarded as a sol- 

 ution of a minute quantity of water in the acetic acid as sol- 

 vent. As the temperature is lowered the acid gradually 

 crystallizes out, with the result that the freezing point of the 

 liquid portion is gradually lowered and the concentration 

 of the water in the acetic acid is increased. Now the 

 specific resistance of the liquid portion decreases on account 

 of the increasing concentration of water. On the other hand, 

 the effective cross section of the liquid between the electrodes 

 gradually decreases and as a result the specific resistance 

 tends to increase. Thirdly, the resistance tends to increase 

 with decreasing temperature because of a true tem- 

 perature effect. Examining the curve it is evident that the 

 concentration factor is predominant above 0°C. This is 

 to be expected as the increase in the concentration of the water 

 in the solution part of the mixture, will be very rapid at first 

 but will gradually decrease. The effect of the second factor, 

 at temperatures near the melting point, will be small compared 

 to the effect of the first factor. With decreasing temp., the 

 volume of the liquid decreases more rapidly and so the second 

 factor will have a gradually increasing effect until finally a 

 temperature is reached when this effect will be equal and 

 opposite to the effect of the first factor. At this point the 

 curve bends and with lower temperatures the second factor 

 is the predominant one, the resistance increasing with 



