Section 113. Description of the Experiments. 5/7 



weighed empty. In the titration of all the portions, the quantity of 

 barium hydroxide solution added was determined by again weighing the 

 flasks containing them after exact neutralization with the base. In those 

 cases where the titration was replaced by a measurement of the con- 

 ductance, each portion was poured in succession into a cylindrical con- 

 dnctance-cell with horizontal platinized electrodes 2.5 cm. apart and 

 measured as accurately as possible, using three resistances in the rheostat. 



The principal error to be feared was that which might arise in the 

 analysis of the cathode portion through the reduction of some of the 

 nitric acid by the electrolytic hydrogen. To reduce this to a minimum 

 the cathode was, as already stated, made as small as possible. Since 

 careful analytical tests* showed (except in one experiment, No. 2, where 

 the cathode was known to be badly arranged) no nitrite or ammonia in 

 the cathode portion or nitrous vapors in the hydrogen evolved, there is 

 good reason to believe that the error from this source was not serious 

 in most of the other experiments. The effect of this error, it may be 

 noted, would be to cause an apparent increase in the transference number 

 of the anion when calculated from the cathode change. 



In case of the 0.002 normal hydrochloric acid solution investigated there 

 was the possibility of an opposite error from the liberation of chlorine at 

 the anode, which would have resulted in too small a transference number 

 as calculated from the anode change. With so very dilute a solution 

 and the low current-density used, there was probably little danger of 

 this ; but to detect any such effect, two different forms of anodes were 

 employed a short platinum wire in experiments 1-5 (see table 122) 

 and a platinum disc in experiments 6, 7, 9, and 10. As the mean results 

 (167.8 and 168.8) with the two electrodes with such different surface- 

 areas agreed almost completely, it seems hardly possible that there was 

 a serious error from this source, especially in the latter experiments. f 



In order to determine what error, if any, might arise in the very dilute 

 solutions from contamination during the experiment, a "blank" experi- 

 ment was made, in which the solution was treated in absolutely the same 

 way as usual except that no current was passed. The stock solution of 



*These tests were made by adding to 10 c.cm. of the cathode portion after its 

 neutralization a few drops of pnre sulphuric acid and some starch solution contain- 

 ing potassium iodide ; by adding to 10 c.cm. of the neutralized portion a few drops of 

 Nessler reagent ; and by conducting the hydrogen evolved at the cathode through a 

 tube containing filter paper moistened with a solution of starch and potassium iodide. 

 All these tests gave a slight positive indication in the one experiment mentioned 

 above, but in no other case, though they were tried in most of them. 



fThe cathodes were also varied in form (since the cathode results were consid- 

 erably higher than the anode results), though there seemed to be no possibility of 

 an abnormal reaction. A platinum disc was used in experiments 1-5, a spiral wire 

 in 6-8, and a short straight wire in 9-10. The form of electrode had no influence, 

 however. In experiment 8 a silver anode was used. 



