In studying second-order lines in the Raman spectra, the main difficulty is the separation of these from the continuous background. At the present time, when the use of low-pressure tubes has become quite general, this difficulty may be regarded as largely overcome. The appearance of low-pressure tubes does not mean that the high-pressure type cannot be used for observing second-order lines. These may in fact still be used on condition that reliable filtration is provided. In the present investigation, low-pressure tubes were chiefly employed. Hence, the customary method may be used in order to measure isolated lines with an intensity of the order of 0.5 units in the scale of  (where the intensity at the maximum of the 802 cm-1 line of cyclohexane is taken as 250).* We note that even this intensity is not the limiting one, since, in a number of practical cases the background had no interfering effect on the measurements.
KeywordsVibrational Spectrum Quinine Sulfate Mercury Line Customary Method Polarization Prism
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