concerning Volta's Contact Force. 459 



to cation intrinsic velocity ujvi. It is remarkable that 

 nothing is wanted except this migration ratio and the con- 

 centration ratio n/n' to calculate in absolute measure the E.M.F. 

 of such a cell, with the same metal at either end. 



A table of correspondences between theory and experiment 

 is quoted from Ostwald and Nernst by Whetham in his B. A. 

 Report, and they agree very remarkably indeed when one 

 considers that the numbers are absolute numbers and might 

 have been in error by large quantities. To illustrate this 

 take a cell with decinormal solution of HC1 on one side and 

 centinormal solution on the other, so that the concentration 

 ratio ft/// =10. 



For the migration ratio we might take Hittorf's own 

 numbers (which he tabulates in the form ul{u + v) &c.) ; but 

 several more recent and presumably more exact deter-. 

 ruinations have been made, and it may be convenient to 

 quote here the table of absolute velocities given by 

 Mr. Whetham as embodying the most recent measurements 

 in 1897. As I write them they give the ionic velocity in 

 mikroms per second for a potential gradient of 1 volt per 

 centimetre (a mikrom being 10 -6 metre or 10 ~ 4 cm., about 

 double the w r ave- length of green lightj. 



... 

 Intrinsic Ionic Velocities. 





u x . 









Vi. 



01 



6-9 







K 



6-6 



I 



6*9 







Na 



1-5 



NG 3 



6-4: 







Li 



3-6 



OH 



18-2 







H 



32-0 



C 2 H 3 2 



3-6 







NH 4 



6-6 



C 3 H 5 2 



3-3 







Ag 



5-7 



So for HC1 the 



migration ratio 



is 











69 











V 



~320~ 



•216, 







and hence the theoretical E.M.F. of such a cell as that just 

 above spoken of, with a weak solution of HOI opposed to one 

 ten times weaker and connected by any single metal, is 



•114 



i T2i ( jlog 10 10 = -0938volt, 



whereas Nernst gives it as observed at *0926 volt. A very 

 remarkable agreement when we consider how the above 

 absolute constant 4?n/^RT, which I have reduced to '114 volt, 

 is constituted. 



As another example take a cell containing two strengths of 



