1903.] and ike production of Helium from Radium. 205 



In this section we are dealing with the emanation, or radioactive gas 

 obtained from radium. Rutherford and Soddy investigated the 

 chemical nature of the thorium emanation* and of the radium 

 emanation,! and came to the conclusion that these emanations are 

 inert gases which withstand the action of reagents in a manner 

 hitherto unobserved except with the members of the argon family. 

 This conclusion was arrived at because the emanations from thorium 

 and radium could be passed without alteration over platinum and 

 palladium black, chromate of lead, zinc dust, and magnesium powder, 

 all at a red-heat. 



We have since found that the radium emanation withstands pro- 

 longed sparking with oxygen over alkali, and also, during several hours, 

 the action of a heated mixture of magnesium powder and lime. The 

 discharging power was maintained unaltered after this treatment, and 

 inasmuch as a considerable amount of radium was employed it was 

 possible to use the self-luminosity of the gas as an optical demonstra- 

 tion of its persistence. 



In an experiment in which the emanation mixed with oxygen had 

 been sparked for several hours over alkali, a minute fraction of the total 

 mixture was found to discharge an electroscope almost instantly. From 

 the main quantity of the gas the oxygen was withdrawn by ignited 

 phosphorus, and no visible residue was left. When, however, another 

 gas was introduced, so as to come into contact with the top of the 

 tube, and then withdrawn, the emanation was found to be present 

 in it in unaltered amount. It appears, therefore, that phosphorus 

 burning in oxygen and sparking with oxygen have no effect upon 

 the gas so far as can be detected by its radioactive properties. 



The experiments with magnesium-lime were more strictly quantita- 

 tive. The method of testing the gas before and after treatment with 

 the reagent was to take -zwuv^h part of the whole mixed with air, 

 .and after introducing it into the reservoir of an electroscope to 

 measure the rate of discharge. The magnesium-lime tube glowed 

 brightly when the mixture of emanation and air was admitted, and 

 it was maintained at a red heat' for three hours. The gas was then 

 washed out with a little hydrogen, diluted with air and tested as 

 before. It was found that the discharging power of the gas had been 

 quite unaltered by this treatment. 



The emanation can be dealt with as a gas ; it can be extracted by 

 aid of a Topler pump ; it can be condensed in a U-tube surrounded 

 by liquid air ; and when condensed it can be " washed " with another 

 gas which can be pumped off completely, and which then possesses no 

 luminosity and practically no discharging power. The passage of the 

 emanation from place to place through glass tubes can be followed by 



* ' Phil. Mag.,' 1902, p. 580. 

 f Ibid,, 1903, p. 457. 



