Lead acetate test for hydrogen sulphide in gas. . tion produced at the lowest rate is quiteapparent. The difference between the and the cubic feetper hour rates is not so noticeable; practically the same resultswould be obtained between the limits of and cubic feetper hour, and these limits were chosen for the method recom-mended. 3. TIME OF EXPOSURE As pointed out in a previous paragraph, the time of exposure isvery important in determining the depth of coloration produced,the sensitiveness of a test being roughly proportional to the , attention may be called again
Lead acetate test for hydrogen sulphide in gas. . tion produced at the lowest rate is quiteapparent. The difference between the and the cubic feetper hour rates is not so noticeable; practically the same resultswould be obtained between the limits of and cubic feetper hour, and these limits were chosen for the method recom-mended. 3. TIME OF EXPOSURE As pointed out in a previous paragraph, the time of exposure isvery important in determining the depth of coloration produced,the sensitiveness of a test being roughly proportional to the , attention may be called again to the tests made withdry paper in dry gas, where there was little difference noticeablebetween tests of one-half and five minutes exposure. The pro-portionality above noted, however, holds good when the testpaper is moist, unless a large amount of hydrogen sulphide is Technologic Paper 41 1 180 181! 189 1901 192 193 182 191 )94 186 187183 184I8IA 195 1 188185196 Fig. 8.—Effect of rate of flow of gas(Described in Table 8) Technologic Paper 41. Fig. 9.—Effect of time of exposure(Described in Table 9) Hydrogen Sulphide Test 27 present in the gas. In this latter case the depth of colorationdoes not increase so markedly with the time; this case is illus-trated in the tests reported in Fig. 9 and Table 9. The papersexposed more than one minute show only slight increase in color,especially in the photographic reproductions, since the characterof the coloration is changed slightly, becoming silvery. This isparticularly true of the tests made with paper H, which had been treated with ammonia. TABLE 9 Effect of Time of Exposure(Illustrated in Fig. 9) [All tests were made in the standard apparatus with gas containing approximately grains hydrogen sul-phide per 100 cubic feet.] Test Paper Time(minutes) Colorproduced(standardcolor No.) Test Paper Time(minutes) Colorproduced(standardcolor No.) 1 BlankBBBBBB 1616263 646566 BlankHHHHHH 545556575859 1 2 3 4 56-7 88-9 99-10 0.
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