CHAPTER I. 



THE ABSORPTION SPECTRA OF AQUEOUS SOLUTIONS OF HYDRATED 



AND NON-HYDRATED SALTS, AS STUDIED BY MEANS 



OF THE RADIOMICROMETER. 



BY E. J. SHAEFFER AND M. G. PAULTJS. 



The object in using the radiomicrometer for studying the absorption 

 spectra of solutions was to work quantitatively. The photographic 

 method gave us the positions of the various bands, and a qualitative, or, 

 at best, very roughly quantitative estimate of the relative intensities 

 of the various lines and bands. The personal equation of the photo- 

 graphic plate, however, always comes into play and, all things con- 

 sidered, we regard the photographic method as useful and reliable 

 mainly in determining the positions of the various lines and bands. 



A more important problem and one more fundamental than the 

 determination of the positions of the lines and bands, is the measure- 

 ment of the relative intensities of these lines and bands and the relative 

 intensities of the different parts of the same band. For this purpose 

 some instrument must be used which measures the intensity of the 

 radiation falling upon it. We selected the radiomicrometer as best 

 adapted to this purpose, it being a thermo-electric junction attached 

 to a loop of non-magnetic wire, and the whole suspended in a magnetic 

 field. The following form was constructed and used: 



THE RADIOMICROMETER. 



The radiomicrometer used in this investigation was built by Dr. Guy. 

 It had a full period of 8 seconds and a sensibility of 8 cm. per square 

 millimeter of exposed junction, candle and scale being at a distance of 

 1 meter. This instrument, therefore, combines very high sensibility 

 with very short period. It had no compensating junction, and this 

 necessitated very careful protection from changes in temperature, from 

 air drafts, and from energy radiations in general; otherwise the zero- 

 point would be unsteady. It was found that by incasing the instru- 

 ment in a tight wooden box of such dimensions that the radiomicrometer 

 was surrounded by a layer of cotton a foot thick, the drift of the zero- 

 point was entirely eliminated if the temperature of the room was fairly 

 constant. It was quite practicable to keep the room at a sufficiently 

 constant temperature for this purpose. The accuracy of the results 

 was greatly increased by keeping the zero-point constant. Precaution 

 was also taken to keep the current which passed through the Nernst 

 glower as invariable as possible. The source of electricity used was a 

 large storage battery, which supplied a very constant current, provided 



9 



