I developed a simple, rapid, and sensitive method for the estimation of a small amount of carbonate in soils. An air-tight plastic bag containing soil sample is first evacuated, then tiled with a definite volume of air followed by the addition of 2 mol L−1 HCl via an attached rubber septum by using a plastic syringe. After about 20 min, the CO2 concentration of the air inside of the bag is determined by a CO2-detector tube. The amount of CO2 released from the soil sample is calculated by adding the amount of CO2 in the air-phase and that dissolved in the aqueous phase, the latter of which is calculated with the aid of the Henry’s law and the CO2 concentration of the air in the bag. The method gave quantitative results with standard CaCO3-quartz powder mixtures. The results for fifteen Ap soil samples agreed with those by the microdiffusion method.
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