Maech 3, 1922] 



SCIENCE 



223 



TABLE II 



Isotopes op Eadioactive Substances 



SUBSTANCE 



Uranium 



Protoactinium 



Thorium 



Actinium 



Eadium 



Emanation .... 

 Polonium 



Bismuth 



liead ,. 



ThalUum 



As potassium is also known to emit a radia- 

 tion of beta particles we should expect the 

 nuclei of atoms of potassium to be transmuted 

 thereby into nuclei of calcium of the same 

 weight, i. e., we should expect to find that 

 calcium consisted of two isotopes isobaric 

 with those of potassium and therefore of 

 weight 39 and 41. As regards this point the 

 only evidence we have available is that fur- 

 nished by the experiments of G. P. Thomson, 

 who states that he found an isotope for calcium 

 at 40 but with the magnetic field at his dis- 

 posal it was impossible to separate lines even 

 two units apart if such had existed for cal- 

 cium. Thomson states, however, that it is cer- 

 tain that one or more isotopes of the weights, 

 39, 40, and 41 were present in his experiments. 

 In some preliminary experiments made by 

 Dempster an isotope of calcium was found at 

 or near 40. He states, however, that the possi- 

 bility of one of weight 39 is not exchided by 

 ]jis results. It will be interesting to see 

 whether future experiments show that calcium 

 has two isotopes of weight 39 and 41. Some 

 additional evidence on this point might be 

 gained by investigating the association of cal- 

 cium with primary sources of potassium and 

 its salts. 



In this connection it is of interest to point 

 out that lithium, sodium and caesium have not 

 been found to be radioactive. Moreover 

 neither lithium and beryllium nor sodium and 

 magnesium have any isotopes in common. 

 CaBsium has been found to have l3ut one isotope 

 of weight 133 and although the isotopes of 

 liarium have not j^et been investigated it would 

 appear to be highly probable that, since the 

 atomic weight of this element is 137.37, it will 

 be found not to have any isotope isobaric with 

 that of cesium. 



(6) Isotopes of cadmium. 



Since the atomic weight of cadmium is 112.4 

 it will be seen that it will likely be found to 

 have a number of isotopes, especially since 

 zinc has been shown to have four and mercury 

 six. 



{c) Atomic weight and atomic number. 



It will be noted that, with the possible excep- 

 tion of K-'-' and the doubtful CI"" Table I does 

 not show any other examples of isobares. There 

 is a remarkable intermingling of the atomic 

 weights and it is particularly noticeable in the 

 ease of ten consecutive integers representing 

 the isotopes of bromine, krypton, and rubidium 

 — Kr 78, Br 79, Kr 80, Br 81, Kr 82, Kr 84, 

 Rb 85, Kr 86, Rb 87. This result makes it 



