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Infrared Dehydration Method for Determining Gypsum Content of Soils¹

ABSTRACT

A Mettler drying unit (Model LP12) and a top-loading balance (Model PL60) were used for determining gypsum in soils. Plotting the rate of weight loss against time upon heating by infrared (IR) radiation (at 123 or 156°C) gave a dehydration curve made of two peaks. The first peak was due to soil moisture and the second to the crystal water of gypsum. Percent gypsum was determined by extrapolation the dehydration curve (vida infra) to rate = 0. The use of computer graphics in developing the curves made this method very rapid (about 15 min per determination). The reproducibility of the IR method ( = 0.48) was better than the barium sulfate method ( = 0.61) over the 2 to 58% gypsum range studies. The accuracies of the two methods were comparable and estimated to be ± 0.3% gypsum when the average of triplicate determinations was used and ± 0.5% gypsum with single determinations.

¹ Contribution from the Dep. of Soils and Water, King Faisal University, Al-Hassa, Saudi Arabia. Supported by the Saudi Arabian National Center for Science and Technology (SANCST) under contract AR-1-018.

² Associate Professor of Soil Chemistry and Assistant Professor of Soil Chemistry, respectively. Present address of the senior author is Univ. of Alexandria Research Center (UNARC), P.O. Box 832, Alexandria, Egypt.

Received for publication December 6, 1982. Accepted for publication August 1, 1983.