of Radium from Uranium. Ill 



was in the non-emanating form, so that the emanation was 

 retained and did not escape freely from the solution. In the 

 purification process an excess of sulphuric acid had been 

 added, and some still remained in the solution after the final 

 precipitations with barium. The radium therefore would be 

 present as sulphate and it is well known that this compound 

 obstinately retains the emanation. Mme. Curie has stated in 

 her Thesis that the activity of radium sulphate is unchanged 

 by shaking with water for a whole day. 



To test this possibility the uranium solution was removed 

 from the bottle, a small quantity of barium nitrate solution 

 was added drop by drop, and the precipitated sulphate filtered 

 off. This precipitate should have contained the greater part 

 of the produced radium. It was ignited, and any emanation 

 evolved sent into the electroscope. No great quantity of 

 emanation was, however, given off. The barium was then 

 got into solution by first boiling with sodium carbonate 

 solution, washing the barium carbonate produced, and 

 dissolving it in hydrochloric acid. The process was repeated 

 until the whole of the barium (and radium) was obtained in 

 solution. The uranium solution was treated with excess 

 of barium to free it completely from sulphuric acid, concen- 

 trated and returned to the bottle. Tests were then carried 

 out on the amount of emanation accumulating both in the 

 uranium and in the barium solutions. That accumulating in 

 the former amounted to about one-third, and that accumulating 

 in the latter to about two-thirds of the amount obtained from 

 the uranium before treatment, and no rapid increase of the 

 emanating power of the uranium solution was observed for 

 the first few days. There are therefore no grounds for 

 believing that the low rate of production was due to the 

 radium not giving up its emanation, or that more radium was 

 present than the original experiments indicated. 



With regard to the hypothesis of intermediate forms of 

 relatively slow rates of change, it is possible, owing to some 

 recent results, to approach the question on more general 

 grounds than formerly. It is clear that as polonium and 

 radium are to be regarded as products of uranium, the other 

 radio-elements, and especially actinium, present in pitchblende 

 probably have a similar origin, and may in fact be the missing 

 intermediate forms. From Rutherford's recent investigations 

 (Phil. Mag. [6] viii. 1904, p. 636 and 'Nature/ Feb. 9th 1905) 

 it appears probable that polonium is the product of the 

 seventh change of the radium atom, and that four out of 

 the seven changes are accompanied by the expulsion of the 

 heavy a particle, in a recent paper by Marckwald on radio- 



