THALLIUM ELECTRODE AND THALLOUS IODIDE. 201 



ion be taken as SO, according to Noyes and Falk, ^ the equivalent 

 conductance of the thallous ion becomes 76.0. 



At 18°C. there are measurements on thallous nitrate by Kolalrausch ^ 

 and von Steinwehr and on thallous sulphate by Hunt. The value 

 65.9 for the equivalent conductance of the thallous ion at 1S°C. has 

 been computed from these measurements ^ by Noyes and Falk. 



We have been imable to find any data from which the equivalent 

 conductance of the thallous ion at 0°C. can be computed. 



For the purpose of determining the mobility of the thallous ion the 

 nitrate was chosen as the most suitable salt on account of its ready 

 solubility and the ease with which it can be purified and dried. 



The thallous nitrate used for this work was prepared from some 

 thallous sulphate which had been carefully purified by Dr. L. T. Fairhall 

 for other work. To a dilute solution of this salt was added a dilute 

 solution of barium nitrate (free from chloride) in equivalent amounts. 

 The solution was filtered from the barium sulphate, evaporated, the 

 thallous nitrate recovered by crystallization and purified by several 

 recrystallizations with centrifugal drainage. Finally the thallous 

 nitrate was melted in platinum. The melt was clear and colorless and 

 there was no indication of decomposition. Careful qualitative testing 

 gave negative results for barium, sulphate, thallic salts, and halogens. 

 A positive test for nitrite was given by the very delicate alpha- 

 naphthylamine-sulphanilic acid reaction. A repetition of this test 

 quantitatively showed that the nitrite present was not over 0.01% — 

 an amount which could not influence the conductivity by a significant 

 amount. A solution of the salt was neutral to litmus and to phen- 

 olphthalein. Spectroscopic examination of the purified thallous nitrate 

 revealed only the characteristic green thallium line X = 535 and very 

 weak lines of sodium. 



The conductivity cells were of the pipette type and were four in 

 number with cell constants 3.058, 0.5610, 0.05316, and 0.0104 at 25°C. 

 The cell constants were determined independently by two observers 

 in accordance "with the method of Kohlrausch, using potassium chloride 

 at both 25°C. and 0°C. A small Leeds and Northrup motor-generator 



5 A. A. Noyes and K. G. Falk, Jour. Amer. Chem. Soc, 34, -479 (1912). 



6 F. Kohlrausch and H. von Steinwehr, Sitzungsber. kgl. pr. Akad. Wiss. 

 Berlin, 26, 581 (1902). 



7 J. F. Spencer, Z. phys. Chem., 76, 360 (1911), has computed the conduct- 

 ance of thallous nitrate solution at 25°C. from the data of Kohlrausch and 

 von Steinwehr at 18°C. using Kohlrausch's temperature coefficient, obtaining 

 147 as the equivalent conductance of TINO 3 and hence 76.4 for the thallous 

 ion. Incidentally it may be worth while to call attention to the fact that 

 Spencer's figures for the 0.02 N and 0.05 N solution are incorrect. Spencer 

 attributed the value'tor the 0.05 N solution to the 0.t)2 N solution and at the 

 same time introduced a wholly extraneous figure for the 0.05 N solution. 



