July 21, 1911] 



SCIENCE 



83 



show that chemical reactions in general are 

 probably much more complex than is repre- 

 sented by the equations which are usually 

 employed to express such chemical changes." 

 The effect of the nature of the solvents on 

 the absorption spectra has been one of the 

 chief points investigated 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 discovered for water, the alcohols, 

 acetone and glycerol. These bands are per- 

 fectly 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 the laboratory of the 

 Johns Hopkins University for the past twelve 

 years. 



The experimental methods employed are 

 essentially those used by Jones and his co- 

 workers in previous investigations of absorp- 

 tion spectra. To the chemist probably the 

 most interesting result obtained in this work 

 is the evidence for the existence of a series of 

 intermediate compounds in the course of a 

 chemical reaction. When, for example, uranyl 

 nitrate is transformed into uranyl sulphate by 

 the addition of sulphuric acid the absorption 

 bands of the former salt gradually shift over 

 to the position occupied by the absorption 

 bands of the latter. " In an example of this 

 kind the bands can be made to occupy any 

 position between the initial and final posi- 

 tions, and it seems probable that when a salt 

 of one acid is transformed in this way into a 

 salt of another acid, there is a whole series of 

 intermediate systems or compounds formed." 



At the present time no method is known for 

 separating these unstable intermediate com- 

 pounds, but the spectrographic evidence is 

 such as to warrant the assumption of their 

 existence and confirms the view that the ordi- 

 ■ nary chemical equation represents only the 

 initial and final stages in a series of reactions. 



The influence of the solvent on the absorp- 

 tion spectra of the different solvents examined 

 is most interesting. The absorption spectra 

 -of the same salt in different solvents are fre- 



quently very different and in a mixture of two 

 solvents the bands characteristic of each ap- 

 pear, the intensity varying with the relative 

 amounts of the two solvents present. The 

 authors attribute the change in the absorption 

 spectrum accompanying change of solvent to 

 solvation rather than to differences in the 

 dielectric constants of the solvents. The 

 authors call attention to the fact that " prob- 

 ably no salts show more characteristic bands 

 than some of the uranous salts in the various 

 solvents: water, the alcohols, acetone and 

 glycerol." The discovery of a strong " water- 

 band," A 4274, in the absorption spectra of the 

 neodymium salts is likely to prove useful in 

 future spectrographic investigations. This 

 band is intense and is free from neighboring 

 bands. 



Cases have been found where it is possible 

 to break up the absorption bands into finer 

 bands by chemical methods. An example is 

 afforded by solutions of uranyl salts in ace- 

 tone. By the addition of hydrochloric acid 

 the uranyl bands are broken up into fine com- 

 ponents, several of the bands becoming trip- 

 lets and some doublets. 



The authors summarize this action of hydro- 

 cliloric acid and other reagents in the follow- 

 ing statement : " The presence of foreign re- 

 agents causes the uranyl bands to become 

 more intense and, in most cases, narrower." 

 It is further noticed that these bands are 

 slightly shifted toward the red. 



Spectrograms have been made at different 

 temperatures varying from 5° to about 80°. 

 As a result of this phase of the investigation 

 the authors conclude that rise in temperature 

 is accompanied by an increase and a broaden- 

 ing of the general absorption in aqueous solu- 

 tion, the bands at the same time becoming 

 more intense. 'The ninety-eight plates of 

 absorption spectra given at the end of the 

 monograph are a credit to both the investi- 

 gators and the printer.' The data compiled 

 within this and the preceding monographs by 

 Jones and Tlhler and Jones and Anderson will 

 undoubtedly prove of much value to future 

 investigators in the field of light absorption 

 by solutions. Frederick H. Getman 



