Density or Specific Gravity

As in the case of density or specific gravity, the refractive index, n, for hydrocarbons varies in relation to their chemical structures. The value of n follows the order n paraffins < n naphthenes < n aromatics and it increases with molecular weight. 

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. 

Three frequently specified properties are density—specific gravity—API gravity, characterization factor, and sulfur content (2,6,7). The API (American Petroleum Institute) gravity is a measure of density or specific gravity (sp gr) ... 

The label on a bottle of concentrated hydrochloric acid. The label gives the mass percent of HCI in the solution (known as the assay] and the density (or specific gravity) of the solution. The molality, molarity, and mole fraction of HCI in the solution can be calculated from this information. 

To be effective, this method must be carried out on samples which have been blanched, and upon peas from which the skins have been removed. The heat applied in blanching drives off gases entrapped in the tissues, and removal of the skins is required to remove air that may be entrapped under them, although it materially slows up the operation and makes it very tedious. In order that there may be consistency in grading, the test must be conducted under closely standardized conditions of temperature and solution concentration. This becomes of considerable importance in borderline cases, and failure to take it into consideration no doubt accounts for some of the inconsistency in results experienced by the industry. The test is not a true measure of tenderness, in that it accounts for variation in skin texture only in so far as maturity affects skin texture. Skin texture is affected by factors other than maturity (4). Other methods for the estimation of maturity based upon density or specific gravity have been suggested by Jodidi (16) and by Lee (22). 

Some of the simplest techniques and instruments are valuable tools for chemical analysis. This chapter is designed to remind students that simple, rapid methods are advantageous in many situations. These methods are often used for quality control purposes. The methods discussed here are melting and boiling points, viscosity, density or specific gravity and refractive index. 

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... 

Another test method (ASTM D4052) covers the determination of the density or specific gravity of viscous oil, such as residual fuel oil, that are liquids at test temperatures between 15 and 35°C (59 and 95°F). However, application of the method is restricted to liquids with vapor pressures below 600 mmHg and viscosity below 15,000 cSt at the temperature of test. In addition (and this is crucial for residual fuel oil), this test method should not be applied to samples so dark in color that the absence of air bubbles in the sample cell cannot be established with certainty. 

Accurate determination of the density or specific gravity of crude oil is necessary for the conversion of measured volumes to volumes at the standard temperature of 15.56°C (60°F) (ASTM D1250 IP 200 Petroleum Measurement Tables). The specific gravity is also a factor reflecting the quality of crude oils. 

The thermal expansion coefficient governs the influence of temperature on density and therefore it is necessary to specify temperature when discussing density or specific gravity. The density of milk is of consequence since fluid milk is normally retailed by volume rather than by mass. Measurement of the density of milk using a hydrometer (lactometer) has also been used to estimate its total solids content. 

A hydrometer is used to determine the density or specific gravity of a liquid using the principles of buoyancy. Buoyancy results from the upthrust on any object immersed or partially immersed in a liquid. Upthrust is developed as a consequence of the weight of the displaced liquid. At the point of partial immersion at... 

Density or specific gravity or API gravity may be measured by means of a hydrometer (ASTM D-287 and D-1298) or by means of a pycnometer (ASTM D-941 and D-1217). The variation of density with temperature, effectively the... 

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. 

Look up the density or specific gravity of a liquid or solid in reference tables. 

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