CHAPTER IV. 

 SPECTROPHOTOGRAPHY OF CHEMICAL REACTIONS. 



INTRODUCTION. 



Prior to these investigations, very little work had been done on the effects 

 produced on the absorption spectrum of a salt in solution when acids and 

 various other reagents that produce chemical reactions were added. Indeed, 

 much of our knowledge of what is in solution is obtained indirectly rather than 

 by a direct knowledge of the composition of compounds while in solution. Con- 

 siderable work on the effect of the introduction of certain radicals, groups, etc., 

 on the absorption spectra of organic compounds has been done, and a fairly 

 complete survey of this work is given in the first chapter. Especial efforts 

 have been made to discuss, as completely as possible, our knowledge of the 

 absorbing and emitting centers of light and heat. 



It is true that a few observers had noticed that in some cases different 

 salts had bands of different wave-lengths, when dissolved in the same solvent. 

 A typical example of this kind is given in the following table. Then again, 

 observers had noted that the bands of one salt of a metal were finer and 

 sharper than the bands of another salt (for example, neodymium chloride as 

 compared with the nitrate in water), but, as far as we know, no effort has 

 been made to study what changes in the bands resulted as one salt of a metal 

 was changed into another salt. 



The following table gives the absorption bands of some double acetates 

 of uranyl according to Morton and Bolton: 2 



For the following double sulphates they give : 



Ammonium uranyl sulphate 4935 



Ammonium diuranyl sulphate .... 4875 



Magnesium uranyl sulphate 



Potassium uranyl sulphate i .... 



Rubidium uranyl sulphate 4885 



Thallium uranyl sulphate , 4905 



Sodium uranyl sulphate 4875 



4890 4620 4450 



4720 4575 4480 



4790 4540 4370 



4790 4540 4370 



4805 4645 4475 



4630 4480 4295 



4775 i 4580 4440 



1 Publication 130, Carnegie Institution of Washington. 



2 Chem. News, 28, 47, 113, 164, 233, 244, 257, 268 (1S73). 



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