564 Wisconsin Academy of Sciences, Arts, and Letters. 
The total amount of energy which a particle absorbs from 
the incident radiation consists of two parts, that which is scat¬ 
tered, and that which flows into the particle and is transformed 
into heat or - chemical energy. On the selective absorption 
theory of the color of water, however, it is necessary to differ¬ 
entiate between what is true absorption and simply obstruction. 
The work of Aitken^ and others^ has shown that the color is 
not of the nature of that due to the scattering by small bodies 
but is a phenomenon primarily dependent on the water itself. 
While the object of this investigation was not primarily that 
of making a check on the selective absorption theory, satis¬ 
factory experimental evidence will be given later in this paper 
to show that it is the correct one. 
For a long time it has been a matter of conjecture as to 
what is the true nature of absorption in an aqueous solution. 
Its characteristic color was at one time thought to be due to 
resonating chemical molecules which responded to light of a 
certain frequency and as a result the color of the correspond¬ 
ing wave-length was absorbed. With the introduction of the 
theory of electrolytic dissociation in 1886 the ion as well as 
the molecule was found to play an important role. The deter¬ 
mination of the relation between selective absorption and dis¬ 
sociation was the purpose of an extensive work carried on by 
Ostwald^ in 1892. It was known, however, that absorption 
was not entirely due to the ions present since non-electrolytes^ 
as well show selective absorption. Jones and Anderson^ came 
to the conclusion that the difference between the absorption of 
molecules and ions must be slight. They showed that the 
solvent affects to a marked degree the power of the solute to 
absorb light. In a later work Jones and Strong found this 
to be true for a number of substances. It was attributed to 
the combination of the dissolved substance with the liquid and 
seemed satisfactorily explained by the solvate theory of solution® 
This theory was also used to explain the results of Jones® and 
Guy,^ which are of great importance in their bearing upon 
1 “On the Colour of the Mediterranean and other Waters.” Proc. Roy. Soc. 
Bdinbg. Vol. 11, p. 472. 1882. 
2 Nature, Vol. 59, p. 461, 1899. 
3 Zeit. phys. Chem., Vol. 9, p. 579. 1892. 
* Cam. Inst. Wash. Pub. 110. 1909. 
Amer. Chem. Journ., Vol. 37, p. 126, 207, 1907. 
®Carn. Inst. Wash. Pub. 130 and 160. 1911. 
® Jones. Amer. Chem. Journ., Vol. 23, p. 89, 1900. 
^ Guy Cam. Inst. Wash. Pub. 190. 1913. 
