THE PROBLEM OK THK ISOTOI'IC ELEMENTS 



81 



Irivalent Bi by a power often will result in a lowering of the decom- 

 position potential by about 18 mV ; in the present example, therefore. 

 9(1 mV would be expected. The break in the euive for pure RaE is in- 

 de(Hl distinct but after all not so sharp as that for RaK -(- Bi ; this is 

 an effect which in the first case is connected with Ihr lad 1 hat the elect- 

 rode could not be covered with a layer of RalO (^xcn il' all Uic IvaK 

 ])i('S('nt were deposited. 



looir 



■K>6 ^-7 *0d *0-9 +1-0 +1-1 *f2 +1-3 *1A- +f5 *1-6 I/oft 



Fig. 3. Anodic deposition of Ihoiium-B peroxide. Concentialion 

 of the solution IQ-i^N in ThB. 



The lack of sharpness becomes still more pronounced with more dilute 

 solutions, e. g. in the case of our experiments with ThB. The solution 

 was about 10~^'^N in ThB. The discontinuity for peroxide deposition, 

 which can be traced more easily than that for metallic thorium-B, occurs 

 at -|- 1.13 V (see Fig. 3). Since the decomposition potential in 0.001 N 

 lead nitrate solution saturated with PbOg occurs at 0.87 V, the displace- 

 ment amounts to 0.26 V. From the concentration difference of nine 

 j)owers often a difference of 9 x 28 = 252 mV would l)e expected from 

 theory, and thus the values agree very well^. Individual difficulties 

 which have been encountered in these determinalions will !)(> examined 

 in the discussion of the experimental details. 



1 If the average value of 20 mV determined by Gumming and Abegg {Z. Elektro- 

 chein. 13, 19 [1907]) is assumed as the displacement per power of ten, then the 

 agreement is less good, yet always passable in view of the largo sources of error 

 in these experiments ; a similar mean value is obtained from our mcasuicments 

 A\iiich are quoted later. 



b npTesv 



