Study of electrolytic dissociation by the Raman effect. I.—Nitric acid

Abstract

In a recent discovery Raman found that when monochromatic light of frequency v is incident upon a substance, the scattered light contains not only light of the original frequency v hut also light of modified frequency v 1 , and the difference in frequency between the two corresponds to an infra-red character­istic frequency v 0 of the molecules constituting the substance. Thus a new field of work has been opened up, in which the infra-red characteristic frequencies of molecules can be determined with as much precision as is possible in the visible and ultra-violet regions of the spectrum. The present investigation has shown a further possibility of the new discovery. On studying the Raman effect in solutions of nitric acid at different concentrations, the author was able to trace the progress in the electrolytic dissociation of the acid by measuring the changes in the intensities of the Raman lines due to the undissociated molecules and of the ions. Thus the method not only gives direct evidence of the phenomenon of dissociation, but enables the determination of its amount as accurately as is possible in the measurement of intensities of spectral lines. The only defect of the method lies in the fact that it cannot be extended to those electrolytes that do not show any Raman lines. The purpose of the present communication is to describe the results with nitric acid.