120 Journal of the Mitchell Society [3Iarch 



mospheric neon was then undertaken by Aston. Fractionations by 

 charcoal absorption yielded no results, but fractional diffusion resulted 

 in a partial separation of the two gases. They showed the same 

 properties and gave identical spectra, differing only in atomic weight. 

 More recently the possible existence of another isotope with the atomic 

 weight 21 has been shown. 



It would seem that heterogeneity has been proved in more than 

 twenty of the common non-radioactive elements. The investigations 

 have been carried on chiefly by the method of Thomson in which the 

 negative electrons were separated and differentiated, and that of Aston 

 in which the positive particles were examined by the application of 

 similar means to the canal rays. Diffusion methods have also been 

 applied with partial success. From the results obtained by either 

 the Thomson or the Aston method the atomic weights can be accurately 

 calculated. It is interesting to note that the results from the Aston 

 method give as whole numbers the atomic weights of all the elements 

 examined. 



From the examination of chlorine it was found that there were 

 present two distinct elements having the atomic weights of 35 and 37 

 respectively. There was a possibility of another in much smaller 

 amount with the weight 39. The atomic weight of ordinary chlorine is 

 35.47 and this is correct to the second decimal place. It is composed 

 mainly of chlorine 35 plus chlorine 37. The relative amounts of these 

 present have been determined and the atomic weight confirmed. 



In argon a companion element was found in very small amount 

 and this had the atomic weight 36. Kr.ypton gives definite evidence 

 of being a mixture of five isotopes and possibly six. The atomic 

 weights are 84, 86, 82, 83, 80, 78. Xenon also shows the presence 

 of five isotopes with possibilities of two more. 



The remaining ten in the list of Aston are homogeneous as to atoms 

 but heterogeneous as to molecules. These are H, He, C, N, 0, F, P, 

 S, As, and I. In these cases only two variants were found in each 

 mixture. 



There is a very striking fact regarding the isotope of helium which 

 was discovered by Eutherford and found to have the mass 3. jAston 

 gives it the atomic weight 4, the same as helium, and that means from 

 his calculations some multiple of 4. It is proper to state that Ruther- 

 ford has questioned the correctness of Aston 's deductions. If Ruther- 

 ford is right, this coincides with the mass of the hydrogen isotope 



