THE PKOBLK.M OV THE ISOTOl'lC ELEMENTS 



So 



The ell'ect ol' adding very sniull amounts o! lead on the de})osition of 

 ThB below its deeomposition potential was studied as well. 



Table 2 elearly shows the decrease in percentage deposition ol TliB 

 from a O.OOIN nitric acid solution on platinum electrodes ( + 0.4 V, 

 ^Hg) ^vith increasing concentration of lead ; in every experiment four 

 electrode surfaces were measured and the mean value was taken. 



Thus up to a concentration of the solution of !()-' N, the deposition 

 is only slightly affected, at IQ-^N a marked fall is already noticeable, 

 and at IQ-^N the deposition is no longer measurable. This method, 

 which can be still further refined by choosing smaller electrodes, still 

 permits the detection of very small amounts of inactive lead, since the 

 addition of another element, e.g. thallium, which is a neighbour of 

 lead, has no noticeable effect on the deposition of ThB even at a con- 

 centration of 10-3NT1. 



100%{- 

 90 

 80 

 70 

 60 

 SO 

 40- 

 30- 

 20 

 10 



J_ 



/^ 



*0-6 *07 *0-8 *0-9 *1-0 *1-1 *1-2 *1-3 *H 



-TT^^TT^ 



■e/o/t 



Fig. 4. Anodic procipitulion oi TliBUg. The lead isotope concent- 

 ration [Pb + ThB] of the solution lO-^X. 



