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Detection and Determination of Gypsum in Soils
Author(s) -
Lagerwerff J. V.,
Akin G. W.,
Moses S. W.
Publication year - 1965
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1965.03615995002900050019x
Subject(s) - gypsum , soil water , chemistry , acetone , sulfate , reagent , ion exchange , mineralogy , inorganic chemistry , environmental chemistry , soil science , geology , ion , materials science , metallurgy , organic chemistry
A rapid, semiquantitative method (I) and a quantitative method (II) are proposed for the determination of gypsum in soils. Method I involves the determination of the degree of gypsum‐unsaturation of an aqueous soil extract nearly saturated with gypsum, i.e., sufficiently dilute to dissolve all gypsum initially present. The unsaturation is determined by electrical conductivity (EC) measurements before and after saturating the extract with reagent CaSO 4 ·2H 2 O. Increasing the water content of the soil in preparation of the dilute soil extract causes an exchange of adsorbed cations for Ca 2+ from gypsum, and the formation of an equivalent amount of sulfate salts of cations other than Ca 2+ (“exchange error”). The error is equal to the difference between the observed and calculated contents of salts‐other‐than‐gypsum in the dilute extract. It has been estimated from EC measurements. Method II is a modification of an existing method, where gypsum is precipitated in the dilute soil extract by acetone. The exchange error is avoided by determining gypsum on the basis of sulfate associated with calcium. The method minimizes several potential errors, such as those due to acetone and ions occluded in the gypsum precipitate. For a group of gypsiferous soils, errors due to Ca 2+ ‐exchange and acetone occlusion averaged about −22% and −3%, respectively. Gypsum contents, and recovery of added amounts of gypsum, as determined independently by Methods I and II, compare favorably for the soils studied.