3025.     SANDS, A. E., GRAFINS, M. A., WAINWRIGHT, H. W., AND WILSON, M. W.  Determination of Low Concentrations of Hydrogen Sulfide in Gas by the Methylene-Blue Method.  Bureau of Mines Rept. of Investigations 4547, 1949, 19 pp.

        Colorimetric method has been developed for determining traces of H₂S in synthesis gas used in the Fischer-Tropsch process.  The maximum concentration of S that can be tolerated to avoid poisoning of the catalyst is 0.1 grain per 100 cu. ft.  The method is applicable not only to synthetic mixtures of CO-H₂ but to coke-oven gas, carburetted water gas, and blue water gas.  Mercaptans, CS₂, and thiophene do not interfere with H₂S determination.  The preferred absorbent for H₂ S is 2% zinc acetate solution.  H₂S is determined by the photoelectric or spectrophotometric measurement of the quantity of light absorbed by solutions of methylene blue produced by the reaction of H₂S with p-aminodimethylaniline sulfate.  Absorption measurements are made with a Klett-Summerson photoelectric colorimeter, employing a No. 66 filter, and with a Beckman spectrophotometer at a wavelength of 745 mμ.  As little as 0.001 grain of S per 100 cu. ft. can be detected by means of this test, when the volume of gas sample is 1 cu. ft.  When the gas contains 0.05 grain of S as H₂S, only 1 per 10 cu. ft. of gas is required, and the result is obtained in less than 30 min.