Hall Effect in a Binary Electrolyte. 471 



So far as I can see, the theory here given is wholly in 

 favour of the negative results obtained by Roiti and Florio ; 

 and it would therefore seem that Bagard has measured a phe- 

 nomenon not contemplated in the foregoing theory. Van Ever- 

 dingen in the paper referred to above supports Bagard ; but 

 this is owing to his having accidentally omitted the factor 

 tO -8 in his numerical work. 



The ionic concentration-fall can be readily calculated for a 

 completely dissociated electrolyte. From equations (iv.) and 

 (ix. a) we get at once 



do 

 dz 



or 



whence 



or 



d log c ft) 2 e 2 , , TT i7r 



Z 2 — Z x ° C 2 jitit X 2 — Xi 



— log^=H(U + V)(^-0 1 ) 



x 2 —x x 



Thus, calling E the P.D. between two transverse electrodes 

 (of the same mettil as the kation) due only to the differences 

 in concentration set up (a case which could be realized by 

 taking an electrolyte such as silver nitrate, for which U and 

 V are very nearly equal), it follows that 



E = *H(U+V) (%-«,) £=£ 



ih 2 ~~ U/-^ 



Taking the case of copper sulphate, we get, as before, 

 U + V = -00119. 



Putting z 2 — Zi — l centim., and — =1 (volt per centim.), 



x 2 Xi 



and H = 20,000 C.G.S. units, we obtain 



E = 12xl0- 8 volts. 



Hence it would appear that in this, or in any other similar 

 experimental arrangement, it would be necessary not only to 

 employ an extremely strong magnetic field, but also a very 

 high primary potential-gradient, i. e. of the order of 10,000 

 volts per centim. This might perhaps be realized experi- 



