614 



Mr. W. A. Borodowsky on Absorption of 



Table III. 

 NaCl (powder). 





a. 



a/t. 



•01 cm. 



•0075 cm. of Al. 



75 



•02 



•0152 



76 



•03 



•0229 



76 



•04 



•0308 



77 



•05 



•0381 



77 



•06 



•0455 



76 



•07 



•0529 



76 



•08 



•0610 



77 



•09 



•0688 



76 



•10 



•0765 



77 



•11 



•0834 



76 



•12 



•0895 



75 



Mean ... 



76 



These tables show clearly that the absorption is directly 

 proportional to the thickness of the matter traversed. Since 

 the cross-section o£ the /3 ray beam is the same for each 

 layer it follows that the absorption in terms of aluminium 

 is directly proportional to the mass of matter of one kind 

 traversed. 



Relation between Absorption and Concentration. 



In order to compare the absorption of solutions of different 

 concentrations we must know the density of the solution, its 

 concentration, and the thickness of the layer exposed to the 

 beam of f3 particles. The quantity of salt in many solutions 

 was exactly determined by chemical methods, and likewise 

 the densities at different dilutions. The results of the above 

 determinations agreed well with the values given in Landolt- 

 Bornstein's tables. 



Let the percentage of salt and water in a given solution 

 be respectively M s and M w , and let D be the density of the 

 solution. Then in a layer of solution of thickness h the 

 amounts of salt and water in the path of the ft rays per sq. cm. 

 cross-section are respectively : 



M, 

 100 



.D.A 



and ^.D.7, 



If A is the absorption in terms of aluminium for pure 



