464 



ON THE ACCURATE MEASUREMENT OF IONIC VELOCITIES, ETC. 



completed in a day. The direct method, in its present form, gives results at least as 

 accurate as the indirect one, and with much less trouble. In dilute solution the 

 determination is generally complete in about half an hour, as the high voltage, which 

 is necessary in such solutions, imparts a considerable velocity to the ions. After 



TABLE VIII. Degrees of Dissociation. 



becoming accustomed to the method, it is easy to perform five or six experiments in a 

 day. In general the total amount of motion for anion and cation was about 

 G centims., with a probable error in reading of about O'Ol centim. for each boundary, 

 i.e., a total error of about 0'3 per cent. The error in measuring the conductivity 

 might be - 5 per cent., and the error in measuring the small amount of current 

 flowing through the apparatus also about O'o per cent. The error in the calibration 

 of the tube is negligible, and, therefore, in a good experiment the transport number 

 should be correct to about 1 part in 300, and the ionic velocities to at least 1 part 

 in 100. As a matter of fact, this degree of accuracy is easily attainable for the 

 transport number. In the case of the separate ionic velocities the accuracy obtainable 

 is not quite so great owing to the accumulation of errors from the various measure- 

 ments involved. 



