774 Wisconsin Academy of Sciences , Arts, and Letters. 
between the two possible tautomeric forms. Neither of the 
two substances in a pure state exhibits absorption but when the 
two are present in mutual equilibrium, that is, when a number 
of molecules are changing from one form to another, a very de¬ 
cided absorption band is formed. In 1905 11 they stated further: 
1. No organic substance shows an absorption band unless a 
possibility for tautomerism exists in the molecule. 
2. This tautomerism may not be due to a labile atom, but may 
be of the same order as that occurring in those aromatic com¬ 
pounds containing the true benzenoid structure. 
3. In all cases of the simpler tautomeric molecule the vibra¬ 
tion frequencies of the absorption bands are very nearly the 
same. 
4. An increase in the mass of the molecule causes a decrease 
in the oscillation frequencies of the absorption band, i. e. a 
shifting toward the red. 
Baly and Desch account for these facts and explain the for¬ 
mation of the absorption band by the same theory as that ad¬ 
vanced by physicists to explain the phenomena of radio acti¬ 
vity, emission spectra, etc., namely the electron theory. 
In 1906 Baly and Stewart 12 applied the principle involved 
in the foregoing to many colored compouds. As a result of 
their investigations they conclude: 
The color of diketones and quinones is due to an oscillation 
or isorropesis between the residual affinities of the oxygen atoms 
which results in the absorption of light in the visible spectrum. 
Also that in order to start the oscillation it is necessary that 
some influence should be present to disturb the residual affini¬ 
ties of the oxygen atoms. When this disturbing influence is 
present there is no doubt that the principle may be extended, 
and that visible color is due to the oscillations between the resi¬ 
dual affinities on atoms or groups of atoms in juxtapposition. 
They also call attention to the fact that the assumption that 
two compounds must be fundamentally different in constitution 
if one is colored and the other not is quite untrustworthy. 
Many compounds can and do exist with all the conditions for 
isorropesis and yet there is lacking the influence to disturb the 
equilibrium between the residual affinities and so the com- 
11 Proc. Chem. Soc., 8T7, p. 766. 
12 Jr. Chem. Soc., 89, pp. 502, 514, 966, 982. 
