CHAPTER I. 



THE ABSORPTION COEFFICIENT OF SOLUTION FOR MONOCHROMATIC 



RADIATION. 



BY E. O. HULBURT AND J. F. HUTCHINSON. 



INTRODUCTION. 



STATEMENT OF THE PROBLEM. 



Experiments have shown that in the case of certain solutions the 

 absorption of monochromatic radiation may be represented by the 

 formula 



7=/ xio--' (i) 



where /o is the original intensity of the radiation, / is the intensity of 

 the radiation after passing through a layer of solution of thickness t 

 millimeters, and a is a quantity, called the absorption coefficient of the 

 solution for the specified frequency of radiation. 



Experiments have also shown that different values of a are obtained 

 if there is any change in: 



(a) the nature of the solvent or of the dissolved substance. 



(6) the concentration of the solution. 



(c) the temperature. 



(d) the wave-length of the radiation, etc. 



To solve the problem of light-absorption in solutions it is necessary 

 to determine the explicit form of the relation between the absorption 

 coefficient a and the quantities of which it is a function. At present 

 our knowledge is far too meager to indicate more than a qualitative idea 

 of the nature of this relation. 



In the present investigation a has been measured in those regions of 

 the spectrum where the pure solvents possess appreciable absorption. 

 It is assumed that the total absorption of the solution is the sum of 

 two parts, the first being the absorption due to the presence of the salt, 

 the second being the absorption due to the pure solvent. In calcu- 

 lating this second part, it is assumed that the absorption due to the 

 solvent is the same as it would be if there were no dissolved salt present. 

 We therefore write 



a = Ac-\-a 



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