ft Rays from Radium by Solutions and Liquids. 617 



The results obtained should thus hold for any source of 

 ft rays. It must not, however, be forgotten that for each 

 experimental arrangement, a curve of absorption for alu- 

 minium must be obtained for purposes of comparison. 



We see from Table IV. that there is a good agreement 

 between the constants of pure substances and the constants 

 deduced for the same substances when dissolved in water. 

 Both electrolytes and non-electrolytes were used, but the 

 value of the constant for each particular substance remained 

 the same throughout, no matter whether in the form of 

 dilute or concentrated solutions or even pure substance. 

 These results show that the absorption of ft rays is propor- 

 tional to the amount of salt present, and is independent of 

 its physical state. The absorption per unit of mass is further 

 found to be greater for heavy atoms (Ca, Sr, Ba), than for 

 light atoms (Na) — a result noted by previous observers. 

 The internal constitution of the atoms therefore plays some 

 part in the mechanism of absorption. 



Absorption as additive property of Matter. 



The absorption by carbon (graphite and charcoal), sulphur, 

 and bromine were determined separately. In the same cell 

 the absorptions by CS 2 and CBr 4 were also found. If the 

 absorption does not depend on chemical change we can 

 calculate the absorption by these compounds from the ab- 

 sorption by their constituent elements. The absorptions per 

 unit mass per sq. cm. of surface of graphite and charcoal 

 were found to be identical — a result previously found by 

 Mr. Orowther. 



The absorption of 1 grm. C = "2066 grm. of aluminium. 

 „ 1 grm. S = -2598 



In one gr. of CS 2 there is '1575 gr. of 0, and the absorp- 

 tion of this amount =-1.575 x *2066 = , 0325 ; in one gr. of 

 CS 2 there is = *8425 gr. of S, and its absorption is = '8425x 

 •2598 = -2189. 



.\ Total absorption according to additive law for one gr. 

 of C-f S 2 = -0325 + -2189 = -2514. 



In a direct experiment with CS 2 it was found that 1*130 gr. 

 of CS 2 gave an absorption '2822 ; consequently 1 gr. CS 2 

 gives an absorption -2497. The difference between the 

 values calculated and found, viz. '2514 and *2497 is 0*7 per 

 cent., which is well within the limits of experimental error. 



For CBr 4 the calculated result was '2598 per gr., and 

 that found experimentally *2668. These again are in good 



