Specific Gravity or Relative Density

Piezocrystals can be used for biomass concentration estimation since the compressibility of a sample is a function of cell concentration and affects the voltage output of the crystal strongly [146]. A more promising technique is acoustic resonance densitometry (ARD) [147, 148]. In this method, the specific gravity or relative density of the cell-containing sample is measured. Blake-Coleman et al. report the application of this method during on-line biomass concentration estimation for cultivations of Erwinia chrysanthemi and E. coli [147, 148], while Kilburn et al. monitored mammalian cell cultures by ARD [149]. The measurements are affected by gas bubbles and foam and thus they must be performed in an external flow loop if these factors are significant. 

The specific gravity or relative density of the battery gives the best indication of its state of charge. A dischai ed cell will have a specific gravity of 1.150, which will rise to 1.280 when fully charged. The specific gravity of a cell can be tested with a hydrometer. 

The specific gravity (or relative density) p,g[ of a material is the ratio of its density p to the density p of pure water at 4 °C (39.2°F) p i = p/Pw = D/D, where is the weight density of water. From this definition, it is apparent that specific gravity is a dimensionless quantity. Whereas the numerical value of density will vary from one system of units to another, the specific gravity has the same value in all systems of units. Since the density of water in the cgs system is 1 g/cm, densities in that system are numerically equal to the specific gravity p(in g/cm ) = p [. 

Usually, engineers utilize the specific gravity or relative density of gases, denoted d or S.G. This dimensionless physical quantity refers to the ratio of the mass density of the gas over that of a reference gas, usually dry air, measured under normal conditions of temperature and pressure (NTP). For ideal gases, the specific gravity relative to dry air at the same temperature and pressure can be written as the ratio of their molar masses ... 

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. 

Density or specific gravity (relative density) is used whenever conversions must be made between mass (weight) and volume measurements. This property is often used in combination with other test results to predict oil quality, and several methods are available for measurement of density (or specific gravity). However, the density (specific gravity) (ASTM D1298 IP 160) is probably of... 

The density (p) of a substance is its mass per unit volume, while its specific gravity (SG) or relative density is the ratio of the density of the substance to that of water (pw) at a specified temperature ... 

API gravity or density or relative density can be determined using one of two hydrometer methods (ASTM D-287, ASTM D-1298). The use of a digital analyzer (ASTM D-5002) is finding increasing popularity for the measurement of density and specific gravity. 

D 1298 Test Method for E)ensity, Relative Density, (Specific Gravity), or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method D4737 Test Method for Calculated Cetane Index by Four Variable Equation ... 

Accurate determination of the density, relative density (specific gravity), or API gravity of petroleum and its products is necessary for the conversion of measured volumes to volumes at the standard temperatures of 1S C or 60T. 

Fig. 4. Terminal velocities in air of spherical particles of different densities settling at 21°C under the action of gravity. Numbers on curves represent tme (not bulk or apparent) specific gravity of particles relative to water at 4°C. Stokes-Cunningham correction factor is included for settling of fine particles.

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. 

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