Radio-actimty of Uranium. 



419 



to the direct emanations from the polonium nitrate. On the top of 

 the plate was laid a sheet of lead to press it tight to the edges of the 

 watch-glass. 



The exposure was continued for twenty -eight hours. On develop- 

 ing, a strong action was seen, strongest in the middle where opposed 

 to the thickest part of the heap of polonium nitrate, and weaker 

 towards the edge. A well-marked action took place all over the 

 plate exposed to the interior of the watch-glass, but it was sharply 

 cut off at the edges. This confirms the previous results — that the 

 emanations from polonium are of a different character to those from 

 radium or UrX, both of which pass through glass, aluminium, and 

 lead. 



29. Another property of polonium sharply distinguishing it from 

 UrX is volatility. The discoverers first obtained it by subliming 

 pitchblende in vacuo. Afterwards they used this property to separate 

 it from bismuth, the polonium and the bismuth sulphides depositing 

 at different parts of the hot tube, 



A strongly radio-active compound of UrX was ignited in a 

 blowpipe flame with the addition of a drop of sulphuric acid. Its 

 radio-activity, on a sensitive plate, was not diminished by this treat- 

 ment. This experiment was tried several times at increasingly higher 

 temperatures, and always with the same result. 



30. Polonium is precipitated by sulphuretted hydrogen, in an acid 

 solution. An acid or neutral solution of UrX is not precipitated 

 by this reagent. Therefore I am justified in saying my UrX is not 

 polonium. 



31. But it is not so easy to settle whether UrX is distinct from 

 radium, although many arguments point to its not being radium. 

 The discoverers of radium give several of its chemical properties, 

 and in most of these UrX and Ra are entirely different. Thus, 

 radium sulphate is said to be insoluble in water and acids, while 

 UrX dissolves easily to a clear solution in dilute sulphuric acid. 

 Radium salts are said not to be precipitated by ammonium sulphide or 

 by ammonia, while UrX is precipitated by both. 



32. It was hoped that doubtful points might be settled conclusively 

 by the spectrum, as both radium and polonium give well-defined and 

 oharacteristic lines, especially in the ultra-violet part of the spectrum 

 where I have chiefly worked. M. Demar^ay* has given a list of some 

 of the principal lines in the radium spectrum between the wave-lengths 

 3649-6 to 4826-3, the one at 3814-7 being ver.y strong, and those 

 at 4683-0, 4340-6, and 3649*6 being next in intensity. He draws 

 special attention to the line at 3814-7 as the line showing first 

 in a compound poor in radium. In none of my UrX compounds have 

 I been able to detect a trace of this line ; on the other hand I have 



* * Comptea Rendus,' toI. 124, p. 716 ; ' Ckem. News,' vol. 80, p. 259. 



