Air Pycnometer Method

The mean advantage of air-pycnometer over the weight difference method is the speed with which the measurements can be made. A single determination of the volume of the soil and water in a given sample at any moisture content may be made in less than two minutes. The volume occupied by air in the sample may then be determined by simply subtracting this volume from the total volume of the soil samples cylinder. 

The procedure of air-pycnomter is based on Boyle s law PjVj = P2V2 in which P and V are gas pressure and volume respectively at a particular temperature. The volume of air space in a sample is measured by observing the resulting pressure when a known volume of gas at a known pressure expands into a lai r volume that includes the air space in the sample. 

Final air pressure in the reservoir with soil sample = 

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