72 SCIENCE PROGRESS 



are those of the argon series and the thorium emanation. 

 There exists strong evidence, therefore, for the belief that these 

 two emanations are higher members of the argon series. 



Dry radium preparations evolve only a small amount of 

 their emanation. The rest is occluded, and decays in that 

 condition ; the subsequent products of decay remain mixed 

 with the radium salt. The whole of the emanation can 

 be driven off by dissolving the radium salt in water, and 

 creating a vacuum above the water surface, or a great part 

 by heating the dry salt. Kolowrat has studied the latter 

 subject in detail, using barium chloride containing radium. He 

 finds that from ordinary temperatures up to 350° the amount 

 of emanation given off is constant and only 1 per cent, of the 

 whole ; above that temperature it increases rapidly, 90 per cent, 

 being evolved at 830 . The amount then falls to 60 per cent, 

 at 920 , and rises finally to 100 per cent, at the melting point of 

 the salt, about 945 . Similar results were obtained with the 

 fluoride. He concludes that it is impossible to estimate the 

 radium present in a solid substance by evolution of the emana- 

 tion unless the substance is fused. 



Henriot has recently published (1908) the results of a re- 

 search on the analogous problem of the absorption of emanation 

 by charcoal. At ordinary temperatures it is completely ab- 

 sorbed ; at higher temperatures the amount gradually decreases, 

 and by heating the charcoal to dull redness the last traces of 

 emanation are expelled. 



Kofler has determined the solubility of the emanation in 

 water and various solutions. The coefficient of absorption — 

 determined by radioactive measurements — in water at 18 is 

 0*270. The presence of dissolved salts lessens the solubility. 

 Hofman, previously, using similar methods, determined the 

 solubility at the temperatures o, 20 , 40°, and 6o°. The co- 

 efficient of absorption was in the respective cases 0*52, 0*28, 

 o*i6, o"i2. It is much larger in such solvents as petroleum and 

 toluol. 



Attempts have been made to estimate its atomic weight by 

 an indirect method, the rate of diffusion. Rutherford and 

 Miss Brooks, and later, Makower obtained results leading to 

 a molecular weight of about 100; Bumstead and Wheeler, by 

 comparing its rate with that of carbon dioxide through a porous 

 plate, obtained the figure 180; the amount of diffusion of ema- 



