T o calculate hydrogen sulfide, use the following equation. H ~ S j
=
y HzS X 719 volume in liters
This calculation is set empirically a t 25’ C. and 760 mm., using the factor 719 ( I S , appendix). T o correct for other conditions of temperature and pressure, the usual gas law equations are used. For the spectrophotometric method, a 25-nil. alicluot is taken of both the final sample mixture and the reference blank. The final calculation is multiplied by 2. The readings should be made at 670 mp. I n both of the above methods, if the concentration of hydrogen sulfide is above the working curve, the solution is diluted to the appropriate range. An analogous dilution must also be performed on the reference reagent blank; the apparatus should be set a t zero again with this solution before measuring the absorbance of the diluted sample. For higher concentrations of hydrogen sulfide (20 p.p.b. and above). the midget impinger has been used successfully. Place 10 ml. of absorption mixture in the midget impinger and aspirate a t 0.1 cubic foot per minute through the mixture for about 15 minutes. (The midget impinger apparatus is especially useful in field work.) Add 0.6 ml. of amine test solution and 1 drop of ferric chloride solution, agitate after each addition, and transfer to a 25-m1. volumetric flask for spectrophotometric determination or to a 50-ml. volumetric flask for colorimetric determination. Dilute to the mark and allow to stand for 30 minutes. Repeat the same procedure (nithout aspiration) for the reference reagent blank, set the apparatus a t zero, and read the absorbance of the sample. Refer to the working curves for amount of hydrogen sulfide present and calculate as before. Preparation of Standard Curves. Because two methods of estimating the amount of methylene blue formed were used, two standard curves were prepared-one with the Klett-Summerson colorimeter and one n-ith the Coleman spectrophotometer. COLORIMETRIC.Add 0, 1, 3, 5 , 7 , and 9 y of hydrogen sulfide separately to 50-ml. volumetric flasks containing 4
