168 Proceedings of Indiana Academy of Science 



other factors may affect the permanency of the color of a solution. 

 Among these may be mentioned the possibility of changing a color's 

 hue or intensity, or both, through the reaction of the solvent and the 

 solute, through the action of the solvent on the container, or through 

 the action of light upon the solution. Many qualitative observations have 

 been made bearing upon the.=e reactions, but little data of a quantitative 

 nature is available. 



In discussing the photo-sensitiveness of salts of metals, Sheppard' 

 states that "the greater proportion of ordinary crystallizable salts of 

 the metals, whether in the solid state or dissolved, are comparatively 

 stable in respect to light. But this stability is certainly relative rather 

 than absolute, being an inverse function of the absorption of light of the 

 bodies, and is, practically, not disconnected with the fact that it is rare 

 for these bodies to be exposed without intermission. ... It has 

 been observed that aqueous solutions of the salts of the heavier, poly- 

 valent metals undergo a gradual change of character on keeping. This 

 change is apparently of the nature of a hydrolytic cleavage of the metal 

 salt, leading by a series of reactions in stages, with concomitant side 

 reactions fixing each stage enduringly and irreversibly as evolved, to 

 the deposition of structurally conformed aggregates of insoluble oxides, 

 sulfides, and ternary and quaternary complexes of varying composition." 



Inorganic Substances Available for Colored Solutions. There are 

 recorded many more or less isolated statements to the effect that various 

 inorganic substances give a certain color in a given solvent, but no 

 general summary or collection of such data has been found. Many of 

 these colors, and particularly certain of those used as qualitative tests, 

 are too transitory to merit consideration in this paper. Others are 

 apparently permanent for a considerable period of time. The original 

 intention was to present a list of those which seemed to offer the most 

 promise of meeting the requirements already stated. The time available 

 has proven too limited for the accomplishment of this compilation; but 

 mention will be made of some of the types of substances which seem to 

 have possibilities, even though their application may be limited. The 

 solutions mentioned are at present being investigated. It is hoped that 

 special apparatus will be available later so that quantitative data may 

 be collected for them. 



Aciueous solutions seem to be by far the most important. Those 

 containing the color-forming elements mentioned in connection with the 

 periodic table, in the form of simple cations, include our most familiar, 

 coloied solutions, such as cupric sulfate, ferric chloride, etc. The color 

 of some of these solutions is markedly changed through the formation 

 of complex cations under certain conditions, as the strongly ammoniacal 

 solutions of cupric, cobaltic, and nickelous salts. It should be men- 

 tioned that pronounced changes of color of solutions of salts of some of 

 the elements takes place on changing the solvent from 1 per cent hydro- 

 chloric acid to 30 per cent acid. The most common anions giving colored 

 solutions are chromate, dichromate, permanganate, feirocyanide, ferri- 

 cyanide, and chloroplatinate. 



^ Loc. cit. p. 318. 



