Section 49. Errors and their Elimination. 123 



removing and shaking the bomb in the usual manner was to cause partial 

 reversion towards the original reading, but not to prevent the recurrence 

 of shifting. To see whether the shifting was due to uneven temperature 

 some experiments were made, such as altering the level of the vapor in 

 the bath and the manner of shielding, but with negative results. The 

 removal of the platinum-black from the electrode almost entirely obviated 

 this trouble, however, for the subsequent bridge-readings with sodium 

 acetate and dilute hydrochloric acid at 218 were constant to within 0.2 to 

 0.3 mm. for a sufficient period. The pressure was reduced to 2 cm. pre- 

 vious to these measurements, as before. The change in reading was ap- 

 parently due either to formation of bubbles on the electrode, or to an ad- 

 sorption effect, but its cause could not be fully determined. 



The use of a polished lower electrode (in Cell 11) gave rise, however, 

 to a similar difficulty under other conditions, namely, to a shifting of the 

 bridge-reading in the direction of decreased conductance at 18 and to a 

 less extent at higher temperatures. This was found to be due to the 

 formation of bubbles and was obviated at 18 by postponing evacuation of 

 the air space in the bomb till after the measurement at that temperature 

 had been made. As a similar effect was observed to some extent at 100 

 and 156, the air pressure was thereafter reduced only to about 12 cm. 

 before the measurements at the three higher temperatures. The subse- 

 quent measurements proceeded satisfactorily, the same method being fol- 

 lowed also after the introduction of the cylindrical electrode (Cell 111). 

 The air pressure that obtains in the bomb at 218, for the usual volume 

 of liquid, after a reduction of the pressure to 12 cm. at 18, is only about 

 two atmospheres, which does not affect the conductance to a considerable 

 extent. 



In order to diminish the adsorption, the rinsing of the bomb with water 

 was omitted in the case of hydrochloric acid, acetic acid, and sodium ace- 

 tate, and a portion of the solution to be measured was left in the cell for 

 some hours previous to the experiment, in order to thoroughly saturate 

 the electrode, a new portion of the same solution being introduced just 

 before the measurements were made. 



The experiments with sodium acetate were at first conducted with the 

 quartz cup in the bomb. The readings with the solutions of it diluter than 

 tenth-normal were not as constant as with other solutes. It was thought 

 that the inconstancy might be due to a contamination of the solution by its 

 attacking the quartz cup and a consequent concentration of the solution 

 within the cup. This difficulty was apparently obviated (cell 111) by the in- 

 troduction of the new form of electrode and quartz insulator as described 

 in section 47. 



