Radioactive Properties of Uranium. 59 



conjecture from higher to lower osmotic pressure. But this 

 osmotic pressure, whilst it might control the diffusion, cannot 

 be imagined as completely analogous to the osmotic pressure 

 as known in fluid solutions. In the case of extremely weak 

 concentration of UrX, the ordinary osmotic pressure would 

 be a vanishing quantity. But in the present case, the forces 

 which guide the diffusion must be extremely great in order 

 to overcome the immense resistance due to friction. These 

 forces can only result from the reciprocal action between the 

 molecules of the parent body and the atoms of its product, 

 and appear to be a special radioactive type. 



Just as UrX is dissolved in its parent uranium, so the other 

 radioactive products should be dissolved in their parent. 

 There are some experimental facts which confirm this sup- 

 position. We know that radium and thorium give out a 

 gaseous emanation as one of their successive products. The 

 emanation is produced at a constant rate, which does not 

 depend on any physical or chemical agencies, but the escape 

 of the emanation from the body is variable in character and 

 dependent on different conditions. For instance, radium 

 and most of the compounds of thorium give off little 

 emanation when in a solid state. The emanation is stored in 

 the body itself in considerable amount. We may suppose that 

 in reality just as UrX was dissolved in uranium, so the 

 radium and thorium emanations are dissolved in radium and 

 thorium. 



When the parent body is dissolved, the emanation is no 

 longer held bound in the solid solution, and it can readily 

 escape from the water. And it is a fact that all substances 

 have the maximum emanating power when dissolved. The 

 increase of emanating power in presence of moisture can be 

 explained in the same manner. 



We know further that generally the solubilities of the 

 gases decrease with the temperature. And indeed the eman- 

 ating power of almost all radioactive bodies increases when 

 the temperature is raised, reaching a maximum at a dull red 

 heat. At this temperature the solubility should be a minimum 

 and all the emanation should escape. 



But the solubility of thorium emanation is not the same in 

 all compounds of thorium. A compound like the hydroxide 

 or carbonate possesses an equal emanating power in the 

 solid state as in solution. This would indicate that thorium 

 emanation, readily soluble in thorium nitrate and soluble 

 in thorium oxide, is not soluble in thorium hydroxide 

 or carbonate. We should then expect that in the last cases 

 the emanating power should not be influenced by variation 



