Redox conditions for hydrogen sulphide persistence

The slow (rather than rapid) coloration of the suspended paper is consistent with the slow rate for the above reaction. For the lead acetate paper in contact with the warmed solutions, that in the more oxidising solution was coloured only slightly while that in the more reducing solution was extensively coloured. These results indicate the presence of sulphide anions and/or compounds in both bottles, but in amounts inversely proportional to the Eh of the solutions. 

From this experiment it can be inferred that, in the vicinity of oxidising sulphides, sulphide anions and/or compounds occur mainly in reducing solutions. Only very small amounts of H2S occur in the gas phase, even over solutions of low Eh. Near to the point of oxidation, COS is formed. These findings confirm that, in moist soils, any H2S will be in solution and thus gas-phase migration of H2S will not be possible. 

The experimental investigations show that H2S does not migrate in the gas phase through soil. However, it migrates through water-saturated soil, probably in solution as sulphide anions and compounds. These are subsequently adsorbed onto soil particles, from which they can be released as H2S. This can be determined in concentrations as low as 0.01 mg using lead acetate paper. 

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