COLOR AND CHEMICAL CONSTITUTION 139 



will be indicated by similar variation in the nature of the color. In 

 many ring compounds where no such arrangement of linkings, as in 

 the benzoid and quinoid classes, is seen, almost no evidence of color 

 can be found. Furfuran, pyrol, camphor and many others of a con- 

 stitution exhibiting double linkings show only general absorption in 

 their spectra. But whenever the benzoid type is present, no matter 

 whether the ring be composed entirely of carbon atoms or not, the 

 conditions for isorropesis are at once favored so soon as unsaturated 

 atoms or groups can be introduced. These groups by their unsaturated 

 condition give rise to new Unkings and then in turn undergo the 

 make-and-break characteristic of substances showing selective absorp- 

 tion. 



Indeed we come to the conclusion that isorropesis is the cause of 

 color in the aromatic series as well as in the aliphatic series. In both 

 series the two modifications which must always be in statu nascendi 

 bave actually been shown to exist. The change of linking, therefore, 

 that must accompany the transformation of one into the other is cer- 

 tainly to be considered as the source of the oscillations which give 

 rise to vibrations in the ether of a free period corresponding to those 

 in the visible region of the spectrum, and hence the development of 

 color in the substance. The application of these ideas to the interpre- 

 tation of color among inorganic compounds is yet to be made. There 

 seems, however, no doubt but that, where residual affinity exists, there 

 may arise some form of oscillation, caused by the make-and-break of 

 these induced linkings as brought about by the molecular movements, 

 which will record itself in definite vibratory motions of the ether and 

 consequently, if these vibrations are of low enough frequency, will 

 indicate color in the compound. Not until something of a more 

 definite nature is known as regards the true spatial arrangement of 

 the atoms in these compounds, can anything of positive value be postu- 

 lated concerning the disturbances which certain atoms may bring to 

 bear upon other atoms or groups of atoms in the molecule. Conse- 

 quently the periods of oscillation that correspond to many of our well 

 known colored salts have received no explanation in terms of those 

 periods so definitely established among the carbon compounds; periods 

 which through spectroscopic evidence have been made to reveal so much 

 concerning the internal vibrations of the atoms in the molecule and 

 of the disturbances within the atoms themselves. 



