76 ROYAL SOCIETY OF CANADA 



The problem of determining the value of the coefficient in the 

 case of thorium emanation has been attempted by Klaus. ^ The 

 difficulties are great, much greater in fact than in the case of radium 

 emanation which is a comparatively slowly decaying one. Thorium 

 emanation has such a short period — decaying to half value in 54 

 seconds — that after a few minutes only a small percentage of the 

 emanation originally present is left to experiment with. 



Working at ordinary temperature, Klaus obtained as values 

 for the coefficient of absorption 1.05 for water and 5.01 for petroleum. 

 If we accept the figures of Hof mann and of Klaus, we find that whereas 

 radium emanation is forty or fifty times as soluble in petroleum as in 

 water, thorium emanation is only five times as soluble in the former 

 as in the latter liquid. It is probable that future work will change 

 these figures, and more especially the latter, for on account of the 

 difficulties and conditions of experiment, Klaus' values only serve to 

 give an idea of the order of magnitude to be expected. They probably 

 do not even approximate the correct values.' 



No other liquids, to the writer's knowledge, have as yet been 

 examined for their absorption coefficients for this emanation: the 

 problem of the variation of the coefficient with the temperature has 

 not been touched at all. 



Absorptive Qualities of Different Liquids. 



It occurred to the writer that the apparatus he was using 

 for the purpose of testing the absorptive properties of charcoal could 

 be utilized to give an idea, in a qualitative manner, of the absorptive 

 capacity of various liquids for this emanation. 



The apparatus with the conditions and precautions of experi- 

 ment need not be described in full as descriptions have already 

 been given in the papers referred to. It will suffice to state here 

 that a tube containing the absorbing liquid under investigation takes 

 the place of the tube which contained the charcoal heretofore. A 

 water-suction pump blows air through this liquid into a Rutherford 

 testing vessel, the air having been dried and charged with thorium 

 emanation, in tubes containing phosphorus pentoxide and thorium 

 hydroxide respectively, on the way. A manometer in the circuit 

 measures the speed of the air flow. The emanation within the testing 

 vessel ionizes the air and the ionization currents are measured by 

 means of an electrometer. These ionization currents are directly 

 proportional to the quantity of emanation in the testing vessel. 



' Phys. Zeit., 6, 820, 1905. 



2 Trans. Roy. Soc, Canada, Sec. 3, I, 85, 1907: Bulletin No. II, Aug. 31st, 

 1906, Phil. Mag., March, 1909. 



