494 POPULAR SCIENCE MONTHLY. 



The Emanation from Radium. 

 The examination of radium revealed a behavior exactly similar to 

 that of uranium, for it too was found to be continually producing a 

 radio-active substance which, when separated from the radium, slowly 

 lost its activity, while the radium from which it was separated slowly 

 regained its original radiating power. In the case of radium this 

 new substance, unlike the uranium X and the thorium X, could be 

 distinguished by other physical properties besides its activity. Thus 

 Eutherf ord found it to be of the nature of a gas. It could be separated 

 from radium by heating the latter, or by dissolving it in water. The 

 radium which had been so treated lost for the time being all but one 

 fourth of its original radiating power, the other three fourths being 

 found in the gas, or emanation, as Eutherford called it. This gas 

 could be carried by means of air currents through long tubes to con- 

 siderable distances from the radium itself, its path through the tubes 

 being easily traced by the fluorescence which it imparted to the glass 

 walls of the tubes. It could be set away in bottles and the change in 

 its activity watched from day to day. In this way it was found to lose 

 about half its activity in a period of four days, while in the same 

 period the radium from which it had been separated regained one half 

 of its lost radiating power. By passing this gas or emanation through 

 a tube immersed in liquid air, Eutherford found that it condensed at 

 about — 150° C. Eamsay has recently found that it appears to have 

 a characteristic spectrum, as have all the elements. This gas, there- 

 fore, seems to be a substance of very definite physical qualities which is 

 produced by the disintegration of the atom of radium in just the same 

 way as the uranium X and thorium X are produced by the disintegra- 

 tion of the atoms of uranium and thorium. But this gas, like the 

 uranium X and the thorium X, has but a transitory existence, for the 

 fact that it gradually loses its activity shows that it passes on into 



something else. 



Induced Radio-activity. 



Nor did physicists have long to look in order to discover this sub- 

 stance into which the emanation from radium is transformed. The 

 Curies found as early as 1899 that when this gas comes into contact 

 with a solid object, the object becomes coated with a film of radio- 

 active matter which can be dissolved with hydrochloric or sulphuric 

 acid, and which is left in the dish when the acid is evaporated. Or 

 which may be rubbed off with leather and found, by means of the 

 property of activity which it possesses, in the ash of the leather after 

 the leather has been burned. This radio-active matter is so infini- 

 tesimal in amount that in no case is it detected in any other way than 

 by its radio-activity. It might, at first, look as though it were nothing 

 but the active gas itself condensed on the surface of the solid object, 

 but since the rate at which it loses its activity is altogether different 



