PREFACE. 



This investigation on the absorption spectra of solutions is a continua- 

 tion of the work of Jones and Uhler and Jones and Anderson, and has been 

 made possible by grants generously awarded by the Carnegie Institution 

 of Washington. The results obtained from the study of about 3000 solu- 

 tions are recorded in this monograph. These include salts of potassium 

 with a colored anion, cobalt, nickel, copper, chromium, erbium, praseo- 

 dymium, neodymium, and uranyl and uranous uranium. 



The effect of the addition of free acids and foreign salts on the absorp- 

 tion spectra is studied at some length and in considerable detail, and results 

 have been obtained which show that chemical reactions in general are 

 probably much more complex than is represented by the equations which 

 are usually employed to express such chemical changes. 



The effect of the nature of the solvents on the absorption spectra of sub- 

 stances dissolved in those solvents has been one of the chief points investi- 

 gated in this work. It is shown that solvents which themselves do not 

 absorb visible light may have a determining influence on the absorption 

 of the dissolved substances. Well-defined " solvent-bands" have been dis- 

 covered for water, the alcohols, acetone, and glycerol. These bands are 

 perfectly characteristic of each solvent, and their existence is regarded as 

 strong evidence for the theory of solvation, upon which work has been in 

 progress in this laboratory for the past 12 years. 



It is difficult to see how the solvent can affect so markedly the resonance 

 of the vibrators unless it forms some kind of a compound or system with 

 the dissolved substance. Indeed, I am inclined to regard this evidence from 

 the absorption spectra of solutions, for the general correctness of the solvate 

 theory of solutions, as being so strong and unambiguous that there scarcely 

 remains a reasonable doubt that dissolved molecules and especially ions 

 combine with more or less of the solvent. This is especially true when we 

 take into account the various other lines of evidence, all of which point 

 to the same conclusion. 



A large amount of work has been done on the effect of temperature 

 on the absorption spectra of aqueous solutions, and the results are here 

 recorded. A special form of apparatus was designed by Dr. Anderson for 

 this work, involving the principle of total reflection from quartz prisms, 

 which was found to work admirably. These prisms being movable in a 

 glass trough containing the solutions, allowed different lengths of the solu- 

 tions, and, consequently, very different concentrations, to be interposed 

 into the path of the beam of light. 



A piece of pressure apparatus with thick steel walls and quartz and glass 

 ends has been devised for work with aqueous and nonaqueous solutions 

 at high temperatures, and we are now studying the absorption spectra 

 of such solutions at high temperatures. 



