618 Absorption of ft Rays from Radium by Solutions. 



agreement, since there are obvious difficulties in the use o£ 

 volatile substances like bromine and carbon tetrabromide. 



These experiments as well as those with the solutions show, 

 as far as they go, that the absorption is an additive property 

 of matter, and that the absorption in liquids takes place 

 according to the same law as in solids. The internal struc- 

 ture o£ the atom has its influence on the absorption, but the 

 arrangement of atoms in the molecule does not affect the 

 absorption at all. 



This result is contradictory to the view expressed by 

 Mr. Allen *. He found that the absorption of the ft rays 

 from radium by ethylene chloride is three times as great as 

 that by ethylene bromide. I have repeated these experi- 

 ments using the cell method. In the cell *239 cm. high the 

 ethylene chloride absorbs as much as '2813 grm. of alu- 

 minium of the same cross-section. In the same cell the 

 ethylene bromide absorbs as much as *5684 grm. of aluminium. 

 Thus the absorption of ft rays by ethylene chloride was one 

 half as great as that by ethylene bromide — a result which 

 fits in exactly with the additive law. 



Further, Mr. Allen found equal absorptions for CHC1 3 

 and CC1 4 , while the result found in the present experiments 

 is less for CH01 3 than for CC1 4 . 



I think the difference between my values and those found 

 by Mr. Allen result from the imperfect experimental method 

 adopted by the latter. He did not take into account the 

 errors arising from the shape of the meniscus and the mass 

 of the vapour in the upper part of the cell. 



We have seen earlier (p. 610) that serious errors may 

 easily arise unless these disturbing factors are eliminated. 

 The experiments described in this paper are free from these 

 sources of error, since the liquids were always contained 

 between two sheets of thin glass. 



Summary. 



1. The activity of the ft particles after passing through 

 layers of solutions is independent of the chemical or physical 

 state of the solutions. 



2. The method of comparing absorption in terms of alu- 

 minium may be applied to homogeneous or non-homogeneous 

 rays and consequently gives comparative results quite inde- 

 pendent of the coefficient of absorption "\." 



3. The absorption is directly proportional to the mass of 

 matter traversed. 



* Loc. cit. 



