430 Mr. G. N. Antonoff on the 



stages. If UrY is intermediate between uranium and UrX, 

 the rise curve to be expected is shown by the dotted curve 

 in fig. 2. There is no evidence that UrY is in this sense an 

 intermediate product between uranium and UrX. At the 

 same time, it should be pointed out that it is difficult to draw 

 such a conclusion with certainty, for it is based on the 

 assumption that all of L rY is separated with UrX. 



The principal difficulty encountered is that there is no 

 direct method of showing that UrY is completely separated. 

 In the case of UrX, the proof of complete separation is quite 

 simple on account of the quantity of UrX, and the penetrating 

 power of its rays, while the comparison of the ft ray activity 

 of uranium before and after separation of UrX is quite 

 definite. There is, however, some indirect evidence that 

 UrY, under certain conditions, is also completely separated, 

 for with small quantities of iron used in successive precipi- 

 tations both UrX and UrY were obtained in diminishing 

 quantities. Large quantities of iron are favourable to a 

 complete separation, but on account of the soft radiation of 

 UrY small quantities of iron had to be used to obtain thin 

 films. With large quantities of iron, the UrX can be 

 separated completely after a few precipitations, as was 

 shown on page 422. It seems very probable that, under 

 such conditions, UrY must be also precipitated more or less 

 completely. 



When large quantities of iron are used in the precipitation 

 UrX and UrY are separated with a thick layer of iron. In 

 consequence of the absorption of the @ rays in this layer it 

 is difficult to draw any definite conclusions from such an 

 experiment in regard to the relative amount of radiation due 

 to the two products. On the other hand, the initial part of 

 the recovery curve of UrX in uranium, treated with a large 

 quantity of iron, should show some indication of the presence 

 of UrY if it is an intermediate product ; but, as we have 

 seen, the recovery curve is quite normal. 



It may be mentioned here that the a ray activity of a film 

 of uranium of known weight before and after treatment with 

 a large quantity of iron was determined ; but no appreciable 

 change of a ray activity was observed. 



In addition UrY does not seem to be a direct product 

 (immediate or otherwise) of UrX, for in such a case one 

 would expect larger quantities of it in old preparations than 

 in those freshly prepared. On the contrary, experiments 

 showed that the amount separated from uranium several 

 years old is of the same order as that separated after a few 

 days from freshly purified uranium. 



