PREFACE. 



The work recorded in this monograph on the absorption spectra of solu- 

 tions is a continuation of that already published by Jones and Uhler (Publi- 

 cation No. 60, Carnegie Institution of Washington), Jones and Anderson 

 (Publication No. 110, Carnegie Institution of Washington), and Jones and 

 Strong (Publication No. 130, Carnegie Institution of Washington). This 

 work, like that recorded in the preceding publications, has been made possible 

 by grants awarded by the Carnegie Institution of Washington. 



The attempt has been made in this work to solve three problems: 



First, to map out the absorption spectra of certain comparatively rare 

 substances. Urbain has generously forwarded Dr. Strong ample quantities of 

 the oxides of gadolinium, dysprosium, arid samarium with which to prepare 

 their salts and study their spectra. We find that the salts of dysprosium and 

 samarium have spectra that are almost as interesting as those of neodymium, 

 with very sharp, characteristic bands. 



Second. Under the spectrophotography of chemical reactions we have 

 studied especially the effect of oxidizing agents on uranous salts. We have 

 used milder oxidizing agents and stronger oxidizing agents, and have dissolved 

 the uranous salt in single solvents and in mixed solvents. When uranous 

 chloride is dissolved in a mixture of alcohol and water, both the "alcohol" and 

 the "water" bands come out simultaneously on the plate. A mild oxidizing 

 agent was found to oxidize the "hydrated" salts and to leave unaffected 

 the " alcoholated " salts. A strong oxidizing agent, on the other hand, oxi- 

 dized both the "hydrated" and the "alcoholated" uranous salt to the uranyl 

 condition. This is, therefore, an example of "selective oxidation." 



Third. By means of the closed cell we have been able to study the absorp- 

 tion spectra of solutions in methyl and ethyl alcohols up to temperatures as 

 high as 195. The absorption bands widen with rise in temperature up to the 

 highest temperatures employed. Colored solutions, therefore, become more 

 and more nearly opaque as the temperature to which the solutions are sub- 

 jected is raised. 



The effect of rise in temperature on the absorption spectra of neodym- 

 ium salts in mixtures of alcohol and water, where both the "alcohol" and 

 the "water" bands appear simultaneously, has been studied. The "water" 

 bands are more affected by rise in temperature than the "alcohol" bands, 

 showing that the "hydrates" are less stable with rise in temperature than the 

 "alcoholates." 



The problems now under investigation include the effect of ions as com- 

 pared with molecules on the absorption spectra of solutions, the effect of 

 high temperature on the absorption spectra of aqueous solutions, and the 

 measurement of the intensity of the various absorption bands by means of 

 the radiomicrometer and thermoelectric junctions. 



It gives me special pleasure to express my indebtedness and thanks to 

 the Carnegie Institution of Washington for the generous support which they 



