Constitution and Stability of Atom Nuclei, 325 



aluminium consists of only one atomic species, and that 

 phosphorus, found by Aston to be a single species, contains 

 only a very small percentage, if any, of an isotope. Thus 

 the three elements of even number contain nearly three 

 times as many isotopes as the three of odd number. 



It is somewhat remarkable that the only odd numbered 

 element in the range between atomic numbers 3 and 27 

 which is indicated by the atomic weights to contain any 

 considerable percentage of isotope, is chlorine. Practically 

 all of the other elements of odd atomic number in this range 

 ■are pure or nearly pure species, with the exception that 

 boron contains a small percentage of a lower isotope, and 

 the writer has predicted that lithium will be found to contain 

 a small percentage of Li 6 . The atomic weight of potassium 

 indicates that it probably contains a small percentage of a 

 higher isotope, while the atomic weights of vanadium, 

 manganese, and cobalt are probably not known with 

 sufficient precision to show whether each is a practically 

 pure species, or contains a very small percentage of 

 isotope. 



Of the elements of even atomic number, helium, carbon, 

 and oxygen have been found to contain no isotopes, sulphur 

 and calcium contain only small percentages of higher isotopes, 

 iron small percentages of lower isotopes, while the less 

 accurate atomic weights of titanium and chromium indicate 

 that they either contain no isotope, or else only a small 

 percentage. Thus in the region of relatively few isotopes 

 only magnesium and chlorine seem to contain very much 

 more than 10 per cent, of isotopes, that is of atomic species 

 other than the most abundant. That the odd numbered 

 elements lithium and boron contain lower isotopes may be 

 due to the fact that the normal atomic species Li/ and Bj 11 

 both have an abnormally high value of the ratio N/P, which 

 may account for the very slight abundance of the more 

 abundant isotope, as well as for the formation of smaller 

 amounts of the lower isotope. 



Fundamental Principles for the Prediction of 

 Isotopes from the Chemical Atomic Weights. 



A number of recent papers have made extensive pre- 

 dictions as to just which isotopes exist, but in every case all 

 of these except those made by the writer, have violated the 

 fundamental relations of nuclear stability and abundance, 

 and so have not been justified by the later discoveries. Thus 



