Specific Gravity and Density

Specific gravity is defined as the comparison of a fluid (liquid or gas) to the density of water or air. It is a common mistake for operators to confuse specific gravity with density. This confusion is understandable, because specific gravity is a method for determining the heaviness of a fluid. Density is the heaviness of a substance, whereas specific gravity compares this heaviness to a standard and then calculates a new ratio. Most hydrocarbons have specific gravities below 1.0. 

Density is calculated by weighing unit volumes of a fluid at 60 degrees Fahrenheit (15.5 degrees Celsius). 

Specific gravity is determined by comparing the weight of a volume of material with the weight of the same volume of water. There are two methods for determining specific gravity  

Industry uses four different ways to express the heaviness of a fluid  

The density of a fluid is defined as the mass of a substance per unit volume. Density measurements are used to determine heaviness. For example, one gallon of water = 8.33 lb crude oil = 7.20 lb gasoline = 6.15 1b 

Most solvents are clear and colorless. If a solvent exhibits some color, it may be an indication of the presence of impurities or conta- 

Refractive index is a characteristic property of solvents and is very sensitive to the composition of solvent blends. Therefore, it is use- 

BP = boiling point or range ST = surfaoe tension at 20 °C, at 25 °C ER = relative evaporation rate (diethyl ether = 1) FP = flash point by olosed cup PGMEAc propylene glycol monomethyl ether acetate (Note Properties are selected from different resources without claiming to be complete and accurate) 

The density (p) of a substance is the mass of its unit volume, and is expressed in g/ml. At4°C, 1 ml of distilled water weights 1 g and so its density at this temperature is unity which is taken as standard. The density at any other temperature t ° is 

Specific gravity values involve several decimal points which are not convenient to use. Therefore, those associated with petroleum industry usually preler to use API gravity, an arbitrary scale (established by American Petroleum Institute) expressed in whole number degrees. API gravity is a derivative of the conventional gravity and is defined as 

When greater accuracy is required or when only small quantities are available, 1 iquid densities are best obtained from the mass required to fill a vessel of accurately defined volume, e.g., a specific gravity bottle (p.217) or a pycnometer. With careful technique, the densities measured with pycnometers are precise to five significant figures. 

For not too viscous liquids available in sufficient amounts, density is more conveniently determined by buoyancy devices namely Westphal balance or a Hydrometer. These devices are based on Archimedes principle according to which the buoyant effect (the upthrust acting on an object immersed in a liquid) is directly proportional to the weight of the liquid displaced. 

A hydrometer is a float caliberated (with water) to indicate specific gravity (usually on API scale) of a 1 iquid by the extent (depth) to which it submerges into the liquid. Though it permits very rapid measurements, a hydrometer is usually employed only where approximate specific gravity is acceptable. 

Although density and specific gravity are nsed extensively, the API (American Petroleum Institute) gravity is the preferred property  

The density of a material is mass per unit volume reported as gm/cm. The density of uncured adhesives is useful in verifying the correct portion of liquid resin and filler ingredients of a formulation. The density of a cured adhesive is an indicator of the specific formulation and of completeness of cure. 

The density of uncured liquid formulations is measured as specified in ASTM D1875, Density of Adhesives in Fluid Form. A weight-per-gallon cup whose volume is exactly 83.2 ml at 25°C is weighed to the nearest 0.1 gram, filled with adhesive, and reweighed. The net weight of adhesive 

The density of a cured, solid adhesive may be measured by taking a small sample of the adhesive (any shape), weighing it (in grams), then immersing it in a graduated cylinder containing a known volume of water (in cm ). The volume of water displaced by the sample is equal to the volume ofthe sample, and density then equals mass/volume. 

Test methods forthe density and specific gravity of cured adhesives are specified in ASTM D792, Density and Specific Gravity (Relative Density) of Plastics by Displacement Specific gravity is the ratio ofthe density of 

For instance, the two allotropic forms of carbon, such as diamond, and graphite, owing to their different space lattice structure exhibit different densities. Actually, diamond owing to its closely packed cubic structure has a specific gravity of 3.512 while the graphite with its loosely hexagonal lamellar packed structure has specific gravity 2.230. 

Staples, L.F. Friedrich Mohs and the scale of Hardness J. Geol. Education, 12 (1964) 98-101. 

Povarennikh, A.S. A Fifteen Division Mohs Scale of Hardness Zap. Ukr. Otd. Vses. Mineralog. Obshchestva Akad. Nauk. Ukr. SSSR 1 (1962) 67-74. OreTlnd 

Povarennikh, A.S. Necessary Revisions to be made in the Mohs Scale of Hardness. Dopovidi Akad., Nauk. Gemstones Ukr. SSSR, 6 (1964) 804-806. 

Mineral or material (in bold the original Mohs minerals) Mohs scale (1822) Rosival scale Ridgeway scale (1933) Povarennyk h scale (1962) Vickers hardness Knopp hardness  

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Density Density and specific gravity NFT 60-101 ISO 3675 ASTM D 1298 Hydrometer... 

Density and Specific Gravity. Water has a density, mass per unit volume, of about 62.4 lb/fU (1.000 g/cc) at 0°C, whereas mercury, also a Hquid, has a density of about 842 lb/ft (13.5 g/cc) at the same temperature. AH things being equal, greater densities mean thicker required tank sheU thicknesses. 

Density and Specific Gravity For binary or pseudobinary mixtures of hquids or gases or a solution of a solid or gas in a solvent, the density is a funcrion of the composition at a given temperature and pressure. Specific gravity is the ratio of the density of a noncompress-ible substance to the density of water at the same physical conditions. For nonideal solutions, empirical calibration will give the relationship between density and composition. Several types of measuring devices are described below. 

The pharmacist often uses measurable quantities such as density and specific gravity when interconverting between weight (mass) and volume. 

Note The values of density and specific gravity, in metric system, are numerically equal, i.e., when expressed in g/cc, the values of density and specific gravity are the same. For example, a density of 1.2 g/cc equals specific gravity of 1.2. 

API gravity a measure of the lightness or heaviness of petroleum that is related to density and specific gravity ... 

Hydrometer. A device for measuring specific gravity of liquids. Its description with Fig is given in Vol 3 of Encycl, p D67, under DENSITY AND SPECIFIC GRAVITY... 

Specific Gravity — tuin 0.883 max 0 888 at 20o/20°(68°/68°F) sball be deed by any convenient method that is accurate to the third place (such as by pycnometer, described in Vol 3 of Encycl, pp D69 to D71, under Density and Specific Gravity)... 

The density and specific gravity of milk vary somewhat with breed. Milk from Ayrshire cows has a mean specific gravity of 1.0317 while that of Jersey and Holstein milks is 1.0330. Density varies with the composition of the milk and its measurement has been used to estimate the total solids content of milk. The density of a multicomponent mixture (like milk) is related to the density of its components by ... 

Radioisotopes are widely used in die measurement of process variables, including the level of liquids and solids in tanks, silos, and other vessels, the density and specific gravity of fluids and solids, the thickness of sheets and coatings, the moisture content of soils and other solids, the mass flow of materials in pipelines or on belts, and the determination of chemical composition of raw materials, in-process materials, and end-products. Representative examples of these applications are given in Table 6. 

Physical Property Variables. These variables are concerned with the physical properties of materials with the exception of those properties which are related to chemical composition and direct mass and weight. Variables included are density and specific gravity, humidity, moisture content, viscosity, consistency, and structural characteristics, such as hardness, ductility, and lattice structure. 

N, Shaking Density. It is a density of an explosive submitted in bulk after it undergoes shaking as prescribed by the BurMines Test (Ref 4, p 24). See under Density and Specific Gravity Determinations of Solids, item w)... 

There are also other methods of measurement (Ref 13, pp 890-92 Ref 23, Method D1070) Density and Specific Gravity Determinations of Solids... 

The procedure rs more rapid if the West-phal Balance is used. This device is described as item b, under Density and Specific Gravity Determinations of Liquid . For detn of sp gr of solids, the plummet is replaced by the sample (in the form of a lump), suspended by a non-corrosive wire... 

Fill a clean 50ml pycnometer, similar to the one described as item c under Determina-n at ion of Densities and Specific Gravities of Liquids , with distd w, freshly boiled and cooled to 10° and insert the stopper provided with a thermometer. Take care nor to introduce air bubbles and to have the capillary of side arm filled with water flush with the top. 

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