172 Dr. Tycho E:son Auren on 



strong increase of *e , H (see Table VII.) for these 



elements ; while there is decrease in intensity of rays of 



a greater wave-length on increasing the thickness of the 



... 

 filter. Values for elements that fall within what is called 



selective absorption range are not comparable with the 



other values. No doubt this range has also extended to 



substances whose atomic numbers lie next below the 



numbers of these elements, but probably the intensity of 



radiation within this section of the wave-length range 



must have been much less. In order, as much as possible, 



to do away with errors that would arise from this cause, 



it does not seem to be advisable to include the values 



obtained when using filter I. for the substances Sr(X K g = 



0-767), Mo (\ K/32 = 0-633), Rh (\, A = 0*537), and for the 



substances Pd (X Kj8o = 0-521) and Ag (A,^ =0*491) when 



filtering with I. and II. 



II. Experimental Results. 



By comparing the absorption coefficients in compounds 

 whose molecules only differ from one another by one or 

 more atoms of oxygen the relative atomic absorption 

 coefficient of this element can be determined. In my 

 first experiments water-solutions of ]S T aC10 3 and NaCl were 

 employed for this purpose : but in the experiments de- 

 scribed below I have preferred to use certain pure organic 

 compounds which, at ordinary temperature, are obtained 

 in the form of liquids. This is done on the ground of 

 absorption for these substances being determined to an 

 appreciably greater extent by the absorption of oxygen 

 than is the case with NaC10 3 and similar combinations, 

 which, in addition to oxygen, contain heavier and at the 

 same time more strongly absorbing substances. The sub- 

 stances used have been free from water and, moreover, 

 in chemical purity the best obtainable. In the following- 

 table are noted down the substances used as well as the 

 values found for k^i-q q in the compositions of radiation 



which have been got by means of the above-mentioned 

 four different aluminium filters (I., II., III., IV.), and 

 also the differences of these values for two compounds 

 which in regard to molecular composition differ from each 

 other only by one atom of oxygen. These differences 

 (*0/H o) tnus indicate the atomic absorption coefficient of 

 oxygen in relation to the molecular absorption coefficient 

 of water. 



