204 EXPERIMENTS IN RADIO-ACTIVITY. 



the adjective "radio-active" be added, the phenomenon of Rutherford 

 is distiiioui.shed from the phenomena ol)served by Russelh In this 

 section we are dealing with the emanation, or radio-active gas obtained 

 from radium. Rutherford and Sodd}^ investigated the chemical nature 

 of the thorium emanation (Phil. Mag., 1902, p. 580) and of the radium 

 emanation (ibid., 1903, p. iST), 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 ))e passed without alteration over platinum 

 and palladiiun 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 s})arking with oxygen over alkali, and also, during several 

 hours, the action of a heated mixture of magnesium powder and lime. 

 The diseharging poAver was maintained unaltered after this treatment, 

 and inasnmch as a considerable amount of radium was employed it 

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

 stration 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 From the main (piantity of the gas the oxygen was withdrawn by 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 the tube, and then withdrawn, the emanation was found to be present 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 has no effect upon the 

 gas so far as can be detected by its radio-active properties. 



The experiments with magnesium lime were more strictly quanti- 

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

 the reagent was to take one two-thousandth 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 

 l)rightly 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 hj'drogen, 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 oft" 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 



