in Inorganic Triple Salts, etc. 421 



quently, may be regarded as particularly labile in their 

 structures and probably capable of giving off and taking 

 on electrons more readily than the others. There are 

 many of these elements, particularly among the metals 

 that form weak bases. It appears that there are a few 

 exceptions among the metals to this connection between 

 color and multiple valency, for cadmium gives a colored 

 oxide, but has, perhaps, no distinct second valency, 

 although two suboxides of it have been described, while, 

 on the other hand, arsenic and antimony give colorless 

 salts and oxides while showing two valencies in each case. 



It is a very common occurrence that chromogenic atoms 

 give different colors, including absence of color, under 

 varying conditions of valency and chemical combination. 

 For instance, the cupric ion is blue, anhydrous cupric 

 chloride is brown, anhydrous cupric sulphate is colorless, 

 cupric oxide is black, cuprous oxide is red, and so on. 



In order to explain such variations as these on the 

 basis of our theory it must be supposed that different 

 chemical combinations and different conditions of valency 

 modify the electronic behavior of the atoms in such a way 

 that their manner of exchanging electrons varies greatly. 



There is a vast amount of knowledge in regard to the 

 molecular structures of organic coloring-matters and con- 

 cerning their various chromophore groups, but it appears 

 that the exact cause of the colors has not been satisfac- 

 torily explained. The present theory, however, if it is 

 a reliable one, will explain these colors, as well as others, 

 by the assumption of electronic exchanges and the result- 

 ing absorption of light. Nitrogen and carbon, under the 

 proper conditions of chemical combination may be sup- 

 posed to show electronic activity, and even oxygen may 

 do this, if our theory is correct, as is shown by the intense 

 blue color of liquid ozone. 



According to our theory everything that is colored or 

 opaque must possess spontaneous electronic activity, and 

 if it is supposed that the conduction of electricity is facili- 

 tated by, or is even entirely dependent upon, this activity, 

 we have a very satisfactory explanation of the well-recog- 

 nized generalization that opacity to light is favorable to 

 electric conductivity. 



