274 Messrs. F. Soddy and T. D. Mackenzie on the 



and left open the question whether this parent was itself 

 formed from uranium, or was present merely as an incidental 

 impurity derived from the mineral. It appeared that the first 

 step to be accomplished was to purify a considerable quantity 

 of a uranium salt by a method calculated to remove the 

 intermediate products as well as the radium. Only in these 

 circumstances will measurements of the initial rate of pro- 

 duction of radium from uranium be definite. This work has 

 occupied a considerable time, and forms the main substance 

 of the present communication. In all about three kilograms 

 of uranyl nitrate have been purified, and it is hoped that 

 these preparations in the course of time will furnish the data 

 sought, although it is already apparent that a very long 

 period of time must elapse. For this reason it has seemed 

 desirable to record full details of the method of preparation 

 and testing of the solutions. The laboratory where the work 

 has been done was new at the commencement of the work, 

 and has been scrupulously kept from contamination with 

 radioactive substances, so that in this respect the conditions 

 have been eminently favourable. 



The method of purification employed in the former ex- 

 periment depended on the resemblance between radium and 

 barium, and on the fact that the latter can be removed with 

 the former by addition of sulphuric acid. It is unlikely that 

 this method would suffice completely to remove the inter- 

 mediate products or products present in the uranium. In 

 the present experiments the uranium was purified differently. 

 Uranyl nitrate possesses the not at all common property of 

 ready solubility in ether. It was considered likely that ex- 

 traction with ether would free the uranium not only from 

 incidental impurities which is known to be the case, but also 

 from the products of its own disintegration. Sir William 

 Crookes (Proc. Roy. Soc. 1900, lxvi. p. 409) in this way 

 separated uranium from uranium X discovered by himself, 

 and now recognized as the first disintegration product. Our 

 present results showed at once that the radium can also be 

 very completely removed from the uranium by this process, 

 and there is every reason to hope that other disintegration 

 products are also completely removed. The extraction of 

 large quantities of uranyl nitrate with ether has proved a 

 somewhat lengthy and troublesome operation, on account of 

 the oxidation of the ether, and the consequent formation of 

 insoluble reduced uranium compounds. In addition several 

 explosions have occurred, resulting in one case in the loss of 

 some of the material undergoing purification, and in another 

 in serious injury to one of the workers, and the loss of three 



