170 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



neighborhood of the critical point, which in this case is 240.6. At the 

 critical point the rapid decrease in conductance with the temperature 

 ceases abruptly and thereafter there is only a moderate decrease as the 

 temperature increases. Between 239.5 and 240.6 there is a conduct- 

 ance decrease of approximately 50 per cent for a temperature change of 

 1, whereas between 240.6 and 252 there is a decrease of less than 

 50 per cent for a temperature change of approximately 12. The sharp 

 break in the tangent to the curve at the critical point is very noticeable. 



800 



400 



ZOO 



SZO* 140* I&O* IRQ* ZOO* ZSO* +0* 



Temperature. 



FIG. 38. Representing the Conductance of Solutions of Potassium Iodide in Methyl 

 Alcohol as a Function of the Temperature through the Critical Region. 



This result is obviously due to the fact that below the critical temperature 

 the observed conductance change is due to the combined effect of tem- 

 perature and of density change, while above the critical point it is due 

 to temperature change alone. 



As the critical point is approached, the salt becomes appreciably 

 soluble in the vapor and is sufficiently ionized to render the vapor a 

 fairly good conductor. In Table LXI, are given values of the specific 

 conductance of liquid and vapor for solutions of ammonium chloride in 

 methyl alcohol, together with the relative volume of the liquid 



V. 



phase -jf. 



