Pycnometer, specific volume determination

The specific volume vs. temperature data were obtained by using capillary dilatometers. Specific volumes at 25°C., determined in a pycnometer, were used as reference. 

The densities of the solvent and of / -lactoglobulin A ( -Lg) in 40% (v/v) 2-chloroethanol, in the presence of 0.01 M HC1 and 0.02M NaCl, were determined, with and without prior dialysis, in a 10-ml pycnometer at 20°C. Solutions were prepared as described previously (8, 24). The solutions were filtered through millipore filters in syringe adapters just before the density measurements. Protein concentrations were determined after filtration by ultraviolet absorption at 278 nm. The apparent partial specific volume, oapp, was calculated from the densities using the standard equation (21, 25) ... 

A preliminary step necessary to precise work with the pycnometer is the determination of its two volume constants that is, the constants of the linear equation expressing die capacity as a function of die temperature. This is done by filling with distilled water and weighing accurately several times at each of two temperatures near the ends of the range for which the pycnometer is to be used. The bottle form is also adapted to the precise measurement of densities of solids. See also Specific Gravity. 

Pycnometer pik- na-m9-t9r [Gk pyknos + ISV -meter] (1858) n. A container whose volume is precisely known, used to determine the density of a liquid by filling the container with liquid and then weighing it. The same instrument may be used to measure the density of particular matter, such as plastic pellets, by immersing it in a liquid that is inert to, and significantly less dense than the solid matter. A dilatometer is a special pycnometer equipped with instruments to study specific volume as a function of temperature. 

True Density or Specific Gravity. The average mass per unit volume of the individual particles is called the tme density or specific gravity. This property is most important when volume or mass of the filled composition is a key performance variable. The tme density of fillers composed of relatively large, nonporous, spherical particles is usually determined by a simple Hquid displacement method. Finely divided, porous, or irregular fillers should be measured using a gas pycnometer to assure that all pores, cracks, and crevices are penetrated. 

Specific Gravity. The specific gravity is determined by weighing a known volume of sample in a Lipkin bicapiHary pycnometer as described in ASTM Designation D941. 

Density (the mass of liquid per unit volume at 15°C) and the related terms specific gravity (the ratio of the mass of a given volume of liquid at 15°C to the mass of an equal volume of pure water at the same temperature) and relative density (same as specific gravity) are important properties of petroleum products as they are a part of product sales specifications, although playing only a minor role in studies of product composition. Usually, a hydrometer, pycnometer, or digital density meter is used for determination in all these standards. 

The density specific gravity) of coke has a strong influence on future use and can affect the characteristics of the products such as carbon and graphite. The density (specific gravity) of coke can be measured conveniently by use of a pycnometer. In the test method (ASTM D5004), the mass of the sample is determined directly and the volume is derived by determining the mass of hquid displaced when the sample is introduced into a pycnometer. Oil or other material sprayed on calcined petroleum coke to control dust will interfere. Such oil can be removed by flushing with a solvent, which must be completely removed before the density determination. 

The bulk density of a powder is obtained by dividing its mass by the bulk volume it occupies. The volume includes the spaces between particles as well as the envelope volumes of the particles themselves. The true density of a material (i.e., the density of the actual solid material) can be obtained with a gas pycnometer. The bulk density of a powder is not a definite number like true density or specific gravity but an indirect measurement of a number of factors, including particle size and size distribution, particle shape, true density, and especially the method of measurement. Although there is no direct linear relationship between the flowability of a powder and its bulk density, the latter is extremely important in determining the capacity of mixers and hoppers and providing an easily obtained valuable characterization of powders. 

A modified pycnometer has also been used by Schurecht for the determination of the volume of test specimens. It consists essentially of a wide-mouth cylindrical glass vessel provided with a ground in, hollow stopper which has a tube in its center. The volume of this piece is computed from the relation v — w — wi + h)/8, where V = volume of specimen w = weight of bottle plus liquid in grams Wi = weight of bottle plus liquid plus specimen b = weight of saturated test piece, and 5 = specific gravity of liquid. 

Density (ASTM D-1298, IP 160) is an important property of petroleum products because petroleum and especially petroleum products are usually bought and sold on that basis or, if on a volume basis, then converted to mass basis via density measurements. This property is almost synonymously termed as density, relative density, gravity, and specific gravity, all terms related to each other. Usually a hydrometer, pycnometer, or more modem digital density meter is used for the determination of density or specific gravity (ASTM 2000 Speight, 2001). 

Density is best measured with a pycnometer (Figure 39-10). The weight of the empty container is determined, then the container is filled with the sample liquid and weighed again. If the volume of the container is known, then the density can be calculated. If the volume is not known, then water can be determined first, and the sample and water values compared. This gives a specific gravity instead of density, but usually the difference is negligible for dilute aqueous solutions. 

The specific mass is the mass of unit volume of the solid components of the soil (without pores). It is determined with the use of a pycnometer. 

Another important property to consider in a PCS system is the density (ppcs)- The definition of Ppcs is expressed by the sum of the products of the weight fraction x, and the density p, of each component as Equation 62.4 define, and it can be obtained by the usage of a specific gravimeter or a pycnometer by determining the volume. Toppi and Mazzarella proposed to calculate composite material properties as function of its composition instead of the necessity of determining the thermal properties on every occasion the composition changes. 

Pycnometer. A small bottle having an accurately-ground glass stopper pierced with a capillary. The bottle is of known volume and is used for the accurate determination of the specific gravity of a material. 

The specific gravity d of an oil is the weight of a given volume of the oil at a specified temperature compared with the weight of an equal volume of water at the same temperature, all weights being taken in air. Generally a pycnometer or Drummond capillaries are used for determination. 

The specific gravity (or relative density) of coconut oil is the ratio of the mass of the coconut oil in air at 30°C to that of an equal volume of water at the same temperature. Determination of relative density (d o) is carried out using a hydrostatie balanee (if it is necessary a precision with three decimal digits) or a pycnometer. 

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