Constant volume piezometers

The group of Safarov, also from Azerbajian, has been active since 2000 and they have measured the pVTx properties of electrolytes (CaCl2, LiNOs, ZnBr2, ZnCl2) and nonelectrolytes (methanol, propanol) over a wide range of temperature and pressure using a constant-volume piezometer. 

To determine the density of liquid freon, the method of a nonballast constant-volume piezometer with membrane-mercury separator was used. The mass of the substance in the piezometer was determined by weighing after freezing out Freon-23 in the separating container. The temperature and pressure were measured using the same instruments as in Ref. [4.3]. Experiments were conducted along the isochores. The maximum error of measuring specific volume fell within the range 0.1-0.2%. 

Shilyakov A. A., Sheludyakov E. P., Soloviov A. N. Experimental study of density of Freon-21 and Freon-114B2 using constant-volume piezometer.—In Thermophysical Properties of Freons. Nauka, Novosibirsk, 1969, p. 6—24. 

For the experimental investigation of compressibility of superheated and saturated vapors, the method of the constant-volume nonballasted piezometer was employed. The fundamental variables (pressure, temperature, and mass of the substance) were measured with instruments of the same class as those used in the work of MEI. The distinguishing feature of the piezometric rig was the use of a membrane zero indicator of pressure of the electrocontact type. The sensitivity of this instrument reached 1 mm water column, but the zero point drifted by 10 mm water column. The authors in Refs. [2.19, 2.21] evaluated the scatter of experimental points on the saturation curve as 0.4% for pressure, and the repeatability of presssure during the forward and reverse tracing along the constant-volume lines was 0.15%. 

C, is a cylindrical glass vessel with a volume of 450 cm. The piezometer contains the solution and 330 gms of Hg. The top of the piezometer is fitted with a Taper joint for filling. A precision bore capillary, E, (2mm in diameter) is fitted to the bottom of the piezometer. The piezometer is suspended (6) in a brass or stainless steel pressure vessel, H. A glass boiler tube, J, encloses the upper portion of the capillary. The pressure vessel is filled with ethylene glycol which serves as a thermal and pressure medium. The entire apparatus is submerged in a constant temperature bath controlled to 0.001 C. The temperature inside the pressure vessel is monitored with a Hewlett-Packard quartz crystal thermometer (to determine when thermal equilibrium is reached after compression and decompression). 

Given the mass m during the successive expansion of the substance from the volume of the main piezometer to the evacuated volume the geometrical constant of the instrument can be evaluated from the relation... 

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