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The Quantitative Determination of Magnesium in Soils Using 8-Hydroxyquinoline¹

ABSTRACT

A comparison of gravimetric, color-imetric and volumetric methods for the determination of exchangeable magnesium in soil by precipitation as 8-hydroxyquinoline was made. When small quantities of magnesium were present in soil extracts, it was found that certain recommended procedures gave inaccurate results. The potassium bromate method gave positive errors which may not always appear in the final results because incomplete precipitation of magnesium quinolate occurs in an oxalate solution. Aluminum may also cause a positive error unless it is completely removed before the magnesium is precipitated. A colorimetric procedure using a photelometer to measure the color intensity of magnesium quinolate dissolved in hydrochloric acid is recommended as a rapid and accurate method for the determination of small quantities of magnesium. Soils low in magnesium as indicated by quick tests using Titan yellow as indicator contain less than 15 milligrams of exchangeable magnesium in 100 grams of soil.

¹ Contribution from the Oklahoma Agricultural Experiment Station, Stillwater, Oklahoma.

² Research Assistant and Professor of Soils, respectively.