A POLAROGRAPHIC TECHNIQUE FOR THE MEASUREMENT OF DISSOLVED SULPHIDE IN WATERLOGGED SOILS

Abstract

SummaryThe polarographic oxidation of sulphide at the dropping mercury electrode reported by Revenda (1934), forms the basis of this technique for the assay of dissolved sulphide in soil solutions.Soil solution is expressed from cores removed from the soil in a Hiller‐type borer, and transferred to tubes containing pyrogallol and NaOH. A current‐voltage curve for each sample is then obtained using the dropping mercury electrode in conjunction with a saturated calomel electrode. The current in the plateau region of a curve is proportional to the sulphide concentration, and after volume and temperature corrections, the sulphide concentration in a sample can be read from a previously prepared calibration curve.The possibility of sulphide loss from the samples before analysis has been found to be slight.Details of construction, and calibration of the dropping mercury electrode using standard Na2S solutions, are included in the description of the technique and apparatus. The inclusion of such minor modifications as (a) the insertion of a condenser across the microammeter terminals to dampen the large current oscillations produced by the dropping mercury electrode, and (b) the inclusion of a switch to allow reversal of polarity at the microammeter, enabled a circuit of the type currently used for soil oxygen diffusion measurements to be used also for sulphide estimation.