Notes on Determination of Carbonates in Soils by Chemical Means, D.T. A., and X-Ray

Various methods for measurement of carbonates in soils were tried and studied. Gas evolution methods are accurate but slow and susceptible to experimental error. Acid neutralization is rapid and offers a fair approximation, but it is affected by many non-carbonate minerals. Versenate methods are rapid and accurate, but are affected by exchangeable calcium on the clay. None of these methods is ordinarily specific for calcite or dolomite. Differential thermal analysis is accurate and specific for calcite or dolomite. Best results were obtained by measuring peak height after runs in an air atmosphere. However, analyses are slow and are influenced by changes in the apparatus. X-ray diffraction from a copper tube is accurate if peak area rather than peak height is measured, but the intensities are sensitive to the presence of iron, which absorbs most of the X-rays. X-ray fluorescence measurement of calcium Kα radiation is accurate and less susceptible to variable absorption, but since this method is affected by non-carbonate calcium, correction by leaching and re-testing is suggested. This appears to be the method most worthy of further examination.