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The ultraviolet (U. V.) absortion of isomerics sodium xylene sulphonate (S. X. S.), lignin substances (hydrotropic, sodium lignin sulphonate of low and high degree of substitution etc.) and their mixtures in the aqueous solutions were measured.It was found that lignin structure-especially one represented by its molecular weight per phenolic OH had an effect on the extinction of lignin.Photometric determination method of S. X. S. in the hydrotropic and hydrotropic-SO2pulping waste or recovery liquor (mixture of lignin substances and S. X. S. in aqueous solutions) was found, applying the so-called “ duplication method ”.U. V. absorptions of an aqueous solution containingx% lignin substances andy% S. X. S. were measured with control ofz% S. X. S. aqueous solution. Here, extinction of solution was x+ (y+z) when x, y and z was extinction of x% lignin, y% S. X. S. and z% S. X. S. in the control respectively.In the range of y≥z, always x+ (y-z) ≥z. In y=z, absorption spectra of the solution might represent one of lignin substances. At spectra of lignin substances and S. X. S. in the range of wave length under 245 mμ, x<<y or x <<z were found. So, in the range y<z, the larger was the difference between z and y, the smaller became x + (y-z) to Therefore the spectra of the solution were curved downwards. Because the spectrum of lignin substances alone, in the range of wave length under 245 mμ had upward curves.In such a way, by measuring the spectra of hydrotropic and hydrotropic-SO2pulping waste or recovery liquor, varing the concentratration of S. X. S. in the control, they can determine the concentration of S. X. S. in the liquor.

Determination of Sodium Xylene Sulphonate and Lignin Substances in the Hydrotropic Process with the Ultraviolet Absorption Method