46 Prof. J. N. Brtfnsted and Prof. G. Hevesy on 



In the case of: mercury, where, as already mentioned, 

 A = 0-0070, the following values of ft M a and M 2 corre- 

 spond to the values of a given in the first column of the 



table. 



Table V. 



a. (3. M 2 . . M r Mj-Mj. 



1 1-00702 202-0 199-2 2-8 



4 1-00877 201-3 197'8 3-5 



9 1-01171 201-1 196-7 4-7 



Consequently we are able to interpret our experimental 

 results by assuming the ordinary mercury as made up of the 

 pure elements 202"0 and 199'2 present in equal amounts or 

 by the elements 201" 3 and 19 7 '8, where the former is four 

 times as strongly represented as the latter, and so on. Our 

 results agree with those of Aston's, found by means of his 

 mass-spectrograpb, in the fact that Aston found a strong- 

 line corresponding to the atomic weight 202 and an un- 

 dissolved band the centre of which corresponds to about 

 199. A very slight quantity of an isotope with the atomic 

 weight of 204, the presence of which follows from Aston's 

 experiments, cannot be found by our method if the separation 

 is not to be pursued very considerably farther. 



For the numeric calculation stated above, we used the 

 results of density measurements made on residual fractions. 

 The calculation can also be carried out by using density 

 data of the distilled fraction s, or reversely the course of 

 the distillation process can be predicted by means of the 

 values furnished by measurements on residual fractions. 

 Whilst the production of the heavy fraction consisted in a 

 steady evaporation of the initial volume 2700 c. cm. until 

 -only 0"2 c. cm. was left, we were for practical reasons — 

 dimensions of our apparatus and working economy — 

 obliged to mix distillates of different quality when endea- 

 vouring to produce the most valuable light fraction. The 

 calculation of the separation proceedings on the basis of the 

 density of the lighter fractions is therefore rendered some- 

 what complicated. In spite of this,, the calculated d d values 

 as shown in Table IV. agree fairly well with the ones deter- 

 mined, though the conformity is not as good as in the case 

 of the d values of the residual fractions. 



