THE TRANSFORMATIONS OF ELEMENTS 545 



This activity could be completely separated along with barium 

 sulphate. Final separation was effected by recrystallising the 

 barium as chloride ; radium chloride is slightly less soluble and 

 separates in the first fraction. In this way crystals were finally 

 obtained nearly two million times as active as uranium. The 

 activity was too great for comparative measurements ; the final 

 fractions were tested for purity by estimating the amount of 

 barium spectroscopically. 



Giesel showed later that the separation could be effected more 

 conveniently by recrystallising the bromides ; the difference in 

 their solubilities is greater than in those of the chlorides. 



Radium continually gives rise to a gas, the Emanation from 

 Radium, discovered by Dorn in 1900, and no intermediate product 

 has yet been detected. A full account of the properties of radium 

 and its emanation will be given in Part II. of this paper. 



When any substance is exposed to the action of the emana- 

 tion it becames coated with an intensely active deposit. This 

 was first observed by M. and Mme. Curie in 1899. It is known 

 as the active deposit of rapid change, and has been found to consist 

 of three consecutive products, Radium A, B, and C. The whole 

 activity decays to half value in 28 minutes, but the decay 

 curve is very irregular. Studies of the rates of decay of the 

 different rays led to the analysis into three separate elements. 

 All three are soluble in strong acids, and volatile at a white 

 heat. B is volatile at the lowest temperature, and can be thus 

 partially separated. 



In 1903 the Curies also observed that substances which have 

 been covered with this active deposit do not lose all their activity 

 after even a prolonged period, Giesel confirmed this. Rutherford 

 found that the activity increases during several years. It is due 

 to the active deposit of slow change, which has been resolved similarly 

 into three consecutive products. Radium D, E, and F. 



Radio-lead (or Radium D) was obtained by Hofmann and Strauss 

 in 1901. The lead obtained from pitchblende was strongly and 

 permanently radioactive — hence the name radio-lead. In 1904 

 Hofmann and co-workers showed that the lead itself is not 

 radioactive, but gives rise to active products separable by 

 chemical means ; the inactive lead slowly regains activity. It 

 therefore contains an inactive element which disintegrates 

 slowly into active products. Rutherford has proved fairly 

 conclusively the identity of the rayless parent, the true radio- 



