ELECTRICAL CONDUCTIVITIES, ETC. 



9 



WATER. 



All of the water used in this work was purified by the method worked out a number 

 of years ago in this laboratory by Jones and Mackay.* It consisted in distilling the 

 distilled water of the laboratory from chromic acid (potassium dichromate and 

 sulphuric acid), which burned up any organic matter present in the water, and then 

 redistilling the water from barium hydroxide. The sulphuric acid held back all 

 ammonia formed from the organic substances, while the barium hydroxide com- 

 bined all the carbon dioxide formed from the oxidation of the organic matter by 

 the chromic acid. 



a; 



w 



Fig. 3. 



When the water was distilled from barium hydroxide, it was distilled first from a 

 Jena glass balloon-flask and the vapor conducted into a retort also containing a little 

 of the hydroxide. The water-vapor after leaving the retort was condensed in a tube 

 of block-tin. By this means 10 to 15 liters of water could be obtained daily, having 

 a conductivitv of from 0.8 to 1.0X10 -6 at zero. 



BATHS. 



The baths used for obtaining the various temperatures were constructed as 

 follows. The zero bath is shown in fig. 3. The bottom of the bath into which the 

 cells were plunged was filled with finely powdered ice moistened with a little pure 

 water. The air above the cells was kept at very nearly zero by suspending just 

 above the cells a pan filled with finely crushed ice moistened with pure water. In 

 this way the solutions whose conductivities were to be measured at zero were 

 kept to within 0.01 to 0.02 of zero. 



*Amer. Chem. Journ., 19, 91 (1897). 



