An accurate wet-combustion method for the determination of carbon in soils

Abstract

1. Inaccurate results previously obtained with wet-combustion methods for the determination of carbon in soils have probably been due to: (a) incomplete oxidation of carbon; (b) incomplete absorption of carbon dioxide. The method described herein ensures complete oxidation and complete absorption. The oxidizing agent employed consists of a mixture of sulphuric acid and potassium bichromate; the absorption takes place in a closed system.2. When highly accurate results are required, a combustion tube is a necessary adjunct to the wet-combustion method, as appreciable amounts of carbon escape complete oxidation in reaction flask.3. The soil should be moistened with water before adding the oxidizing mixture, to avoid the formation of complexes, which may protect part of the carbon from oxidation by the acid.4. Within limits, the concentrations of sulphuric acid and potassium bichromate do not affect the results.5. While it is necessary to use catalysts (selenium and potassium sulphate) for the complete oxidation of the resistant carbon of coal, catalysts were found to be unnecessary for the determination of carbon in soils.6. For soils rich in chloride, it is necessary to absorb the chlorine evolved by means of sodium bisulphite solution.