Sulphur in soils. I.—Determination of readily soluble sulphates in soil

A review is given of techniques proposed for the determination of sulphates in soils. Classical methods for sulphate determination are not, in general, suitable for determining readily soluble sulphates in soils. Sulphate in a 0.001N‐hydrochloric acid extract of soil (40 g. of soil in 100 ml. of acid) can be directly titrated with 0‐02N‐barium chloride by using sodium rhodizonate as an internal indicator. Bromocresol purple used to screen the rhodizonate indicator increases the sensitivity and the ease of detection of the end‐point. The method is simple, rapid and free from serious interference. Results were within the limits of ± 0.5 mg. of SO₄ per 100 g. of soil for soils having a sulphate content of about 10 mg. of SO₄ per 100 g. of soil; from soils of higher sulphate content, errors amounting to less than 5% can be expected. The method is applicable to soils of a wide range of organic matter and sulphate contents.