﻿Absorption of X- Rays and Fluorescent X-Ray Spectra. 997 

 Table III. — Absorption Coefficients (X) a 



Radiation : the homo- 

 geneous fluorescent 

 radiation (series K) 

 from elements below. 



Fe 

 Co 

 Ni 

 Cu 

 Zn 

 As 

 Se 

 Br 

 Sr 

 Mo 



Air 



(76 cm. 

 &0°C). 



•0165 

 •0136 

 •0109 

 •0090 

 •0053 

 ■0044 

 •0039 



•00127 

 •00077 



SH 2 



(76 cm. 

 & 0° 0.). 



•204 



•181 



•149 



•121 



•104 



•06 



•049 



•044 



•0248 



•0137 



•0060 



so 2 



C.,H,Br 



CH,I 



(76 cm. 



(16'6 cm. 



(13-5 cm. 



&0°C). 



& 0° 0.). 



& 0° C). 



•24 



•112 



•384 



•20 



•089 





•166 



■071 



•319 



•134 



•057 



•273 



•112 



•047 



•225 



•066 



•028 



•132 



•0546 



■024 



•11 



■030 



•021 



•098 



•0281 



•071 



•060 



•0160 



•046 



•085 



•0079 



•0236 



•020 



As the rays absorbed become more penetrating (as measured 

 by any substance whose spectral lines are far removed) than 

 a spectral line of A or B, the absorption in that particular 

 substance rises in the manner shown in fig. 1, and ultimately 

 approximates to proportionality again for radiations far 

 removed from the spectral line. 



It may be remarked, too, that the absorption in S0 2 is as 

 much greater than in SH 2 as may be expected from the law 

 that the total absorption is the sum of the atomic absorptions. 

 From the most accurate experiments on the absorption by 

 S0 2 and SH 2 it is evident that the absorption in oxygen is 

 about 1*3 times that in air (neglecting the absorption due to 

 scattering). The absorption by hydrogen is neglected. 

 This result is interesting from the fact that the ionizations 

 in the gases S0 2 and SH 2 are in the reverse order of 

 magnitude *. 



Summary. 



Continuing the work of Barkla and Sadler, the absorption 

 of radiations whose penetrating power is close to that of the 

 spectral lines of the absorbing substances has been investi- 

 gated in detail. 



The relation between the absorption in an element T\ and 

 the absorption measured in a substance whose spectral lines 

 are far removed is found to be practically identical for all 

 substances experimented upon. 



One curve is drawn showing the relation for all substances. 



The relations in the neighbourhood of spectral lines of 

 series K and series L are, however, widely different. 



The absorptions in various gases and vapours have been 

 determined and the generality of the laws further verified. 

 * Barkla and Simons, Phil. Mag. Feb. 1012, pp. 317-333. 



