Hydrostatic weighing technique HWT

The high pressure cell (1) located in an electric furnace (2) contains a hollow cylindrical float made in steel. This float is suspended of a nichrone wire which passes through coils fixed to the upper cylindrical cap. The cylinder is connected to two intermediate vessels (3) which avoids direct contact of the sample with the oil of the press (9) and receive the solution displaced from the cell upon heating. The vessels are half-filled with mercury, above which the sample is present in the left-hand vessel and the oil in the right-hand one. The later contains a movable contact (4) to check that mercury has not been ejected into the oil system. The system 

The resonance frequency is related to the mass, m, of the vibrating tube by 

The typical accuracy in density measurements using this technique is between 0.3% and 0.5%. 

improved with a phase-locked loop for driving the oscillation (Majer et al, 1991b) was used by Wood and co-workers for measuring the pVTx properties of several metal halides aqueous solutions. Later, this group modified the VTD to improve its accuracy and reliability at higher temperatures. The Hastelloy U-tube was replaced by a platinum-rhodium alloy, more resistant to corrosion, and the new VTD assembly included two permanent magnets and soft-steel pole pieces to increases the magnetic field. The new VTD version was used in supercritical aqueous solutions up to 450 and 38 MPa. 

Pick-up Coil and Magnet Drive Coil and Magnet 

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