Hydrostatic weighing technique

Hydrostatic weighing—technique to estimate percent body fat based on the density of an individual. Density is measured by immersing the person in a tank of water. 

P sical Testing. Glass transition temijeratures were measured with a DuPont 990 thermal analyzer. Reported values of T for the Epon 828/MDA networks (Table III) were extrapolated to zero rate from measurements made at heating rates of 5> 10, and 20°C/ min. Epon/DDS network Tg s were measured at 10°C/min. Bulk densities were measured at room temperatiire employing hydrostatic weighing techniques (37). 

For both techniques, the absolute specific voltune of the sarrrple must be krrown at a single condition of pressme and temperature. Normally, these conditions are chosen to be 298.15 K arrd normal pressure (101.325 kPa). There are a nttmber of methods to determine speciQc volrrrrres (or densities) rrrrder these conditions. For polymeric samples, hydrostatic weighing or density gradierrt colrrrttrrs were often used. 

This kind of technique was used by Russian groups, as those of Mashovets, Puchkov, Zarembo and others since the 1960s. For instance, Dibrov et al. (1963) reported a hydrostatic weighing apparatus as shown in Figure 2.7. 

The film may be removed from the substrate and the density determined by displacement techniques.Pycnometry involves the displacement of a liquid or gas from a container of accurately known volume and the weight of the sample. Density gradient columns utilize a thermal gradient to produce a density gradient in a liquid. The sample will float at a level of the same density fluid. Calibration floats are used to determine the density. Fluids having densities of up to 3.3254 g/cm (methylene iodine solution) are available. The most accurate techniques have been developed to study radiation-induced void formation in metals, and they utilize hydrostatic weighing (in and out of a fluid) of small samples (30 mg) with a microbalance to a precision of 0.04%. 

---