Ugt Air Gas Pycnometer

Our air or gas pycnometer is an innovative measuring instrument for the determination of the air-filled pore volume, the solid volume as well as the solid density (dry bulk density) of a substrate sample in the laboratory. Especially the pore volume is a decisive factor for the evaluation of a soil for many questions of water balance, soil management or soil remediation. Air and water conductivity, as well as water and nutrient retention capacity are directly related to pore volume.

How does our air pycnometer work?

The measuring method is based on the fact that only the solid volume VF of a solid sample displaces gas, while pore or void volumes are filled with gas. The air or gas pycnometer consists of a measuring chamber and an additional chamber, which forms the additional volume Vz. The known additional volume is filled with compressed air or the connected gas and connected to the measuring chamber containing the substrate sample via a shut-off valve. Opening the valve results in pressure equalization within the two volumes.

When used as an air pycnometer, atmospheric air is supplied as compressed air via the integrated compressor. Use as a gas pycnometer via the external gas connection enables measurement with gases with defined properties, excluding the effects of air components and humidity (absorption and corrosion).

Application areas

Our air or gas pycnometers are suitable for undisturbed soil samples as well as for bulk materials such as sands, gravels or plant granules.

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• For soil samples with a very high proportion of fines, the applicability of the air pycnometer may be limited, among other things because nitrogen is deposited on the soil particles and distorts the measurement result (Amoozegar et al. 2022). Air pycnometers are therefore only suitable for samples with coarse to medium pores. The same applies to operation with nitrogen.
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• The use of gas pycnometers is therefore particularly recommended for soil samples with a high proportion of fines (e.g. clay).
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The large measuring chamber with a volume of approx. 2100 cm³ enables the examination of correspondingly large samples.