474 Dr. Tycho E:son Auren on the 



X. a.k. and X. m. k., and the absorption coefficient of the 

 element in question is always compared with the absorption 

 coefficient for water. Since, as shown above^ the relative 

 absorption coefficients are independent of the wave-length, 

 and so are more easily to be exactly determined than the 

 absolute absorption coefficients, and since they, as a rule, in 

 different elements, plainly differ from each other, the relative 

 atomic or molecular absorption coefficients may probably 

 very well have the faculty of characterizing different species 

 of atoms or molecules. 



In making the inquiries which I am going to describe 

 in the following pages I have tried to determine the relative 

 absorption coefficients for several elements. As it has been 

 found possible to determine the wanted constants in solutions, 

 and as many elements are attainable without difficulty in the 

 form of solutions, whereas they cannot at all or only with 

 difficulty be obtained in solid or gaseous state, under con- 

 ditions to allow the examining of absorption, I have chiefly 

 made use of solutions. From the many experiments made on 

 the absorption of X-rays, we infer that, " Though the experi- 

 ments undertaken in cases of different density, temperature, 

 and chemical combination may not nearly possess the required 

 degree of experimental accuracy so as to eliminate every 

 influence on absorbability, it may be stated as certain that 

 the power of absorption is essentially determined by the 

 properties of the atom "*. In calculating the relative atomic 

 absorption coefficients from the values of the molecular ab- 

 sorption coefficients of the elements examined, I have, 

 consequently, started from the principle that the absorption 

 of the solution is additively determined by the absorption of 

 the constituent atoms. 



II. Method of Investigation. 

 In order to exclude errors due to incessant changes in 

 hardness and intensity of the radiation, as well as only to 

 have to make null-point-adjustments, my experiments have 

 been arranged in the following manner. Two pencils of 

 rays have been made to pass, one through the element the 

 X. m. k. of which is to be determined, and the other through 

 a sheet of water the thickness of which could be varied. The 

 thickness of the water sheet is regulated so that the intensity 

 of both the pencils of rays is equally great. This, on the 

 other hand, can be determined by observing when the 

 currents of saturation in two ionization-chambers, into which 



* PoM, Die Physik der Rontgenstr allien, p. 91 (1912). 



