148 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



TABLE L. 

 CONDUCTANCE OF Ba(N0 3 ) 2 AND MgS0 4 IN H 2 AT HIGH TEMPERATURES. 



Barium Nitrate. 



Concentration Temp. 18 100 156 218 281 

 0.08 N A 81.6 257.5 372 449 430 



Magnesium Sulphate. 



Temp. 18 100 156 218 



0.08 N A 52 . 136 133 75.2 



It will be observed that the maximum lies below 281 for barium nitrate, 

 while for magnesium sulphate the maximum lies between 100 and 156. 

 The more complex the salt the lower the temperature and the lower the 

 concentration at which the maximum appears. As we shall see presently, 

 this is due chiefly to the fact that the ionization of salts of higher type 

 falls off more rapidly with the temperature than does that of the binary 

 salts. For strong acids, the maxima lie at temperatures considerably 

 below those of the binary salts. For hydrochloric acid the maximum 

 lies in the neighborhood of 240 and for nitric acid in the neighborhood 

 of 200 at a concentration of 0.08 N. 



The conductance-temperature curve of sulphuric acid, which is a 

 dibasic acid, has a peculiar form, which has an important significance. 

 Below are given values of the equivalent conductance for sulphuric acid 

 at a series of temperatures at concentrations 0.002 and 0.08 normal. 



TABLE LI. 

 CONDUCTANCE OF H 2 S0 4 AT HIGH TEMPERATURES. 



Concentration 18 25 50 75 100 128 156 218 306 

 0.002 N 353.9390.8 501.3 560.8 571.0 551 536 563 637 



0.08 N 240 258 306 342 373 408 440 488 474 



It will be observed that, at the higher concentration, sulphuric acid 

 exhibits a relatively flat maximum at a temperature of about 250, while 

 at the lower concentration it exhibits a maximum at about 100 and a 

 minimum at about 160, after which the conductance again increases 

 and presumably passes through a maximum at a temperature above 306. 

 At still lower concentration the maxima and minima become more pro- 

 nounced. As Noyes and Eastman 7 pointed out, this behavior of sul- 

 phuric acid appears to be due to the fact that ionization takes place in 

 two stages according to the equations: 



* Noyes, Joe. cit., p. 270. 



