6U 



Mr. R. D. Kleeman on the Secondary Cathode 



The curves obtained are quite distinct from one another 

 and resemble one another in some respects. They show that 

 the elements fall into groups corresponding to the periodic 

 classification. 



























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t5(3 70 84 98 112 126 140 154 ' 168 182 K 



Atomic Weisrht. 



The first sample o£ cobalt used in these experiments gave 

 98 for the value of (Co— Al), a value which did not make 

 cobalt fit in with the other elements. The explanation was 

 found to be that, since the cobalt was in the form of very 

 fine powder, it had become more or less oxydized, which 

 decreased the amount of radiation owing to the presence of 

 matter of much smaller atomic weight than that of the 

 cobalt. A determination with a fresh sample of cobalt of a 

 coarser nature gave 181 for the value of (Co — Al), and this 

 made cobalt fit in with the other elements. 



The third and fourth curves in the figure, corresponding to 

 the first and second long periods of the elements, resemble 

 each the letter S in shape ; while the second and fifth curves, 

 corresponding to the second short period and the fourth long 

 period, resemble each the letter S inverted. 



