772 Wisconsin Academy of Sciences, Arts, and Letters. 
tense color, but are precipitated unchanged from this solution 
by the addition of water. It is easy to understand how the 
tetravalent oxygen in quinones, being basic, might add on the 
elements of phenols as well as acids or how it might add on 
the elements of a molecule of water. While it would not be 
wise, however, without very careful investigation, to say it 
were impossible, it is not easy, without altering our present 
conception of the tetravalent oxygen, to see how the same oxy¬ 
gen could be able to form addition products with organic 
nitrogen bases, such as phenylendiamine, and even with po¬ 
tassium hydroxide, which Richter represents it as doing. 
In 1879 Nietzki * 8 formulated a rule, supposed to be of general 
application, that the pigments of most simple construction are 
yellow and by increase of molecular weight they gradually 
change from yellow to red, then to violet, then to blue. 
Schuetze 9 in 1892 found that Nietzki’s rule holds only in 
certain cases; but that changes in color in general are the re¬ 
sults of changes in selective absorption in the regions of the 
visible spectrum. The results of Schuetze’s investigations are 
summed up as follows: 
1. A change of absorption from violet toward red usually 
causes the following changes in color; greenish yellow, yellow, 
orange, red, reddish violet, violet, bluish violet, blue, bluish 
green, etc. Passing through the colors in this direction 
Schuetze calls deepening or lowering the tint; in the opposite 
direction, raising the tint. 
2. Definite atoms and atomic groups by their entrance into 
the molecule cause, for compounds of the same chromophore in 
the same solvent, a characteristic deepening or raising of the 
tint. Those which deepen the tint are called ‘ ‘ bathochrome ’ ’ 
groups or elements, those which raise the tint are called “hyp- 
sochrome” groups or elements. 
3. Hydrocarbon radicles are always bathoehromic. Conse¬ 
quently in homologous series the shade always deepens as the 
molecular weight increases. 
4. The same deepening of color is caused in the groups of 
the periodic series as the atomic weights increase. 
*Verhandl. des Vereins fur Befoerderung der Gewerbfleisses., 58, p. 231 
(Quoted by Schuetze, Zeit. fur Phys, Chem., 9, p. 109). 
9 Zeit. fur Phys. Chem., 9, p. 109. 
