Measurement of Volume Using Helium Pycnometer

Differential counterbalance twin top loading electronic balance. 

When the solid sample of volume Rg is placed in the sample cell, the equation can be written as 

After pressurizing to about 120 kPa above ambient pressure, the state of the system is given by 

Here P2 indicates a pressure above ambient and U2 represents the total moles of gas contained in the sample cell. When the solenoid valve (2) is opened to connect the added volume RaIo that of the cell Vc, the pressure will fall to a lower value P3 given by 

Substituting P2( c 4) from the equation for fi2 R Pa changes the equation into 

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