Part IV. 



CONDUCTIVITY AND IONIZATION OF SILVER NITRATE, POTASSIUM 



SULPHATE, AND BARIUM NITRATE UP TO 306, AND 



OF MAGNESIUM SULPHATE UP TO 218. 



31. OUTLINE OF THE INVESTIGATION. 



The purpose of the present investigation was to extend the conductivity 

 measurements already made with sodium and potassium chlorides to other 

 di-ionic salts, to tri-ionic salts, and to di-ionic salts containing bivalent ions, 

 so as to ascertain the behavior of salts of different types. 



The new salts thus far studied are silver nitrate, potassium sulphate, 

 barium nitrate, and magnesium sulphate. Experiments with the first 

 three substances have been made at 18, 100, 156, 218, 281, and 306, 

 while those with magnesium sulphate have been carried only up to 218 on 

 account of the hydrolytic decomposition of the salt. At each temperature 

 with each salt (except magnesium sulphate) the measurements were made 

 at four concentrations, approximately 0.1, 0.05, 0.0125, and 0.002 normal. 

 Some of the measurements on the salts previously studied by Noyes and 

 Coolidge were repeated as an independent check on the accuracy of the 

 results ; for a new bomb and a different set of measuring instruments 

 were used in this investigation. Incidentally an experimental study has 

 also been made of the change of the conductance-capacity of the bomb 

 with the temperature, as this is an instrumental factor of importance in 

 all these investigations. 



32. DESCRIPTION OF THE APPARATUS AND METHOD. 



The apparatus used was similar to that employed in the previous inves- 

 tigation. Only such parts as are different will be described below. 



THE CONDUCTIVITY VESSEL OR BOMB. 



The bomb was lined only with platinum when the measurements up to 

 218 were made ; but at the higher temperatures, it was found necessary 

 to flow gold over the platinum in the lower part of the bomb, in order 

 to make it perfectly tight. 



The form of the bomb which will be designated "cell i" consisted of the 

 platinum-lined steel vessel previously described, fitted with a fused silica 

 cup, 1.45 cm. in diameter and 1.47 cm. in height, within which a flat plati- 

 num-iridium electrode 1.35 cm. in diameter was placed. 



In "cell n" the fused silica cup and platinum-iridium electrode were 

 replaced by an irregular-shaped platinum-iridium electrode, approximately 



71 



