546 SCIENCE PROGRESS 



lead, with radium D, and of the active products with E and F. 

 He found that the activity of the short-life deposit from radium 

 practically vanished after two days ; thereafter there was a slow 

 increase during eighteen months. The new activity was due to 

 both a and ^ particles. Two experiments showed the nature 

 of the changes. A deposit on a platinum wire, after standing 

 for some considerable time, was subjected to the action of heat. 

 Below 1000° it was unaffected. Between 1000" and 1050° some 

 part volatilised. It no longer gave off a particles, while the 

 /3-ray activity decreased rapidly, falling to half value in six 

 days. During the same time a rays were emitted in slowly 

 increasing amounts. 



Clean surfaces of metallic bismuth placed for some time in 

 solutions of the slow-change deposit removed 90 per cent, of the 

 substance emitting a particles. The bismuth thereafter emitted 

 these a particles, activity decreasing somewhat slowly ; the 

 half-life period was 143 days. The /3-ray activity of the solution 

 remained unaltered by this treatment ; after the bismuth was taken 

 from the solution the latter commenced slowly to emit a ra3's. 



A simple explanation is given by the assumption of three 

 elements : radium D (rayless) ; E, giving /3 rays only ; and F, 

 giving a rays only. D is volatile below 1050°; E does not 

 volatilise at that temperature. D is the parent of E, for after it 

 has volatilised the amount of E rapidly becomes less. F volati- 

 lises at 1050°, for the wire loses its a activity. It is produced 

 from E, for the a activity of the wire is slowly regained. F, alone 

 of the three, is deposited on bismuth from solutions, and it is the 

 element whose half-life period is 143 days. 



Meyer and Schweidler consider that this hypothesis does not 

 completely satisfy the peculiarities of the curve of decay. They 

 suggest a further intermediate product (thus RaEj and RaEo). 



Rutherford has shown the identity of poloniTun, radio-teUurimn, 

 and radium F. Polonium was the first radioactive substance 

 discovered by Madame Curie. The sulphide precipitate from 

 acid solutions of pitchblende contained an active substance, 

 which associated itself with bismuth. With this element its 

 properties are so closely allied that it is impossible to effect 

 a complete separation. Madame Curie repeatedly precipitated 

 the nitric-acid solution by water. The precipitate contains 

 most of the active material. Marckwald obtained the same 

 substance by dipping a rod of bismuth or antimony' in the 



