Specific Gravity

Specific gravity is the ratio between an object s density and the density of water. Specific gravity, is, therefore, dimensionless and does not depend on the units. 

Specific gravity will always have the same numerical value, regardless of the units of density you choose to employ in determining the specific gravity. Any sample with a specific gravity greater than 1 is denser that water. Any sample that has a specific gravity less than 1 is less dense than water. 

There is often some confusion between specific gravity and density, because the density of water is 1.00 g/mL. This means the density expressed as grams per milliliter and specific gravity of a sample are numerically equal. For example, let s calculate the specific gravity of mercury, which has a density of 13.6 g/mL. 

Specific Gravity. The specific gravity of a liquid is the ratio of its weight to the weight of an equal volume of pure water at the temperature of its maximum density (4°C.). This applies alike to pure liquids such as acetic acid and to solutions. 

Substances dissolved in water change the specific gravity, and since specific gravity is one of the properties of a liquid most easily measured with great precision, it is much used by chemists for determining the concentration of solutions which are known to contain only a single dissolved substance. 

Specific gravity of lignified cellulose fiber (wood flour, saw dust, and rice hulls) in WPCs typically is between 1.3 and 1.5 g/cm. Rice hulls lignocellulosic matrix in WPC materials is of about the same density as that of wood flour, and they are equal to about 1.35 g/cm and 1.30-1.35 g/cm, respectively. However, because rice hulls contain 19% of silicates (specific gravity approximately 2.8 g/cm ), the resulting specific gravity of rice hulls as a tiller is around 1.50 g/cm.  

Long fiber cellulosics, such as flax, hemp, jute, ramie, coir, sisal, and cotton, all have density in WPC materials also in the 1.3-1.5 g/cm range. 

Density (specific gravity) of WPCs does not depend on the particle size of the wood flour. It appears that during compounding and extrusion, cellulose fiber is compressed to the maximum density of 1.3-1.5 g/cm.  

A simple formula for the calculation of specific gravity of a composite material is as follows. If we take 100 g of a composite material, containing, say, 50% w/w of HOPE d = 0.96 g/cm ), 30% of wood flour (d = 1.30 g/cm ), and 20% of talc (d = 2.8 g/cm ), each of these components take the following volume  

For 85% wood-flour-filled polypropylene calculations of density (specific gravity) would be as follows  

The specific gravity is the ratio of weight of equal volumes of a substance to that of another substance usually water. For petroleum products it is customary to measure the ratio at 15.6 °C (60 °F) 

The specific gravity of oligo-polyols is determined by the classical method, using a pycnometer, at constant temperature (usually at 25 °C). The Standard Test Method for the specific gravity determination in polyols is ASTM D4669 [36]. 

The specific gravity of the clays is about 2.6. It is difficult to measure the specific gravity of montmorillonite because it swells, but it is calculated that the value is close to that of the kaolins. 

The determination of the specific weight of a substance is frequently of great service. Sometimes it affords a rapid means of distinguishing between two substances similar in appearance sometimes in determining the quantity of an ingredient in a mixture of two liquids, as alcohol and water and frequently in determining approximately the quantity of solid matter in solution in a liquid. It is the last object which we have in view ill determining the sp. gr. of the urine. 

An aqueous solution of a solid heavier than water has a higher-sp. gr. than pure water, the variation in sp. gr. following a. regular but different rate with each solid. In a simple solution— one of common salt in water, for instance—the lu-oportion of solid in solution can be determined from the sp. gr. In complex solutions, such as the urine, the sp. gr. does not indicate the proportion of solid in solution with accuracy. In the absence of sugar and albumen, a determination of the sp. gr. of urine affords an indication of the amount of solids sufficiently accurate for usual clinical purposes. Moreover, as urea is much in excess over other urinary solids, the oscillations in the sp. gr. of the urine, if the quantity passed in twenty-four hours be considered, and in the absence of albumen and sugar, indicate the variations in the elimination of urea, and consequently the activity of disassimilation of nitrogenous material. 

To determine the sp. gr. of substances, different methods are adopted, according as the substance is in the solid, liquid, or gaseous state is in mass or in powder or is soluble or insoluble in water. 

Solids.—The substance is heavier than water, insoluble in that liquid, and not in pmoder.—It is attached by a fine silk fibre or platinum wire to a hook arranged on one arm of the balance, and weighed. A beaker full of pure water is then so placed that the body is immersed in it (Fig. 1), and a second weighing made. By dividing the weight in air by the loss in water, the sp. gr. (water = 1.00) is obtained. Example  

Weight of iron filings and sp. gr. bottle filled with w ater 148.337 Weight of sp. gr. bottle containing iron filings and filled 

An unusual specific gravity indicates that a sample has been tampered with. 

Age can not be tested using urine. There is a rumor that approximate age can be detected in urine, and is tested in medical insurance exams. It s a myth. 

Closely related to density is specific gravity. Specific gravity compares the density of a substance to the density of a reference substance. Typically, for solids and liquids, this reference substance is water at 4°C, 

Note that the specific gravity has no units. When reporting the specific gravity, the temperature of the sample and the reference substance are also noted. The typical format is with a superscript and a subscript. The superscript is the temperature of the substance, while the subscript is the temperature of the reference substance. 

The density of gold at 20°C is 19.3 g/mL. What is the specific gravity of gold  

The majority of mineral fillers have a higher specific gravity than do epoxy resins and will, therefore, increase the specific gravity of the fully cured product. The increase in specific gravity is in proportion to the loading volume of the filler. 

TABLE 9.10 Arc Resistance, s, of DGEBA as a Function of Filler, Loaded to Produce an Initial Viscosity of 4000 to 5000 cP at Working Temperature, and Cured with a Stoichiometric Amount of Listed Curing Agent22 

Fillers with a density lower than that of epoxy can be used to provide reduced specific gravity in cured products. These are usually gas-filled microballoons. Although they generally bring about a significant increase in viscosity, the microballoon filled epoxies (sometimes called syntactic foam adhesives) are often used in marine applications where low density and buoyancy are important criteria. 

Properties of an epoxy system filled with glass microballoons are shown in Table 9.11. Other low-density microballoons, based on phenolic and other materials, have been developed for use in epoxy adhesive formulations. 

Fiber density may be used as an aid in fiber identifieation. Fiber density may be determined by using a series of solvent mixtures of varying density or specific gravity. If the speeifie gravity of the fiber is 

Often densities are expressed by means of spedfic gravity, defined as the ratio of the density of a substance to that of a standard substance. For solids and liquids, the standard substance is usually water for gases, it is usually air. For example, the density of ethanol (ethyl alcohol) at 20°C is 0.7895 g/mL. The specific gravity of ethanol at 20 C referred to water at 4°C is given by 

For an exact value of specific gravity, the temperatures of the substances should be specified. In this case, the notation specific gravity of ethanol at 20°CV4°C shows that the specific gravity is the ratio of the density of ethanol at 20°C to that of water at 4°C. 

Color is one of the more useful properties for identifying substances without doing any chemical or physical tests. A violet vapor, for example, is characteristic of iodine. A red/brown gas could well be bromine or nitrogen dioxide (NOj) a practiced eye can distinguish between the two. Just a small amount of potassium permanganate (KMn04 in solution provides an intense purple color. A characteristic yellow/brown color in water may be indicative of organically bound iron. 

A term often associated with hazardous materials and water is miscibility. If a chemical is miscible with water, it will mix with water, which could make clean up difficult. If the chemical is not miscible with water, it will form a separate layer. The layer will form on top or on the bottom of the water, depending on the specific gravity of the liquid. Most flammable liquids are lighter than water and immiscible, so they float on the surface. 

Gas Composition Chosen Total Inert/Combustible Lower Upper 

Fire and Explosion Hazards Handbook of Industrial Chemicals 

Some specific gravities of common petroleum liquids are 1 to 1.1 for asphalt, 0.8 for gasoline, and 0.6 for naphtha. 

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Because of their widespread use for simple process control, hydrometers are frequently calibrated, not in specific gravity, but in some units related to it, which bear (or bore at one time) some relationship to the concentration being so measured. 

Overall formula Structural formula Molecular weight Bolling, point, °C (1 atm) Specific gravity < (liquid)... 

In oil bearing formations, the presence of polar chemical functions of asphaltenes probably makes the rock wettable to hydrocarbons and limits their production. It also happens that during production, asphaltenes precipitate, blocking the tubing. The asphaltenes are partly responsible for the high viscosity and specific gravity of heavy crudes, leading to transport problems. 

The specific gravity of a pure hydrocarbon is linked to its H/C ratio, the specific gravity decreasing as the H/C ratio increases. Table 3.2 illustrates this variation for hydrocarbons having 14 carbon atoms. 

It is based on the observations that the specific gravities of hydrocarbons are related to their H/C ratios (and thus to their chemical character) and that their boiling points are linked to the number of carbon atoms in their molecules. 

Crude oil base Speclflc gravity of heavy gasoline cut, Specific gravity of residue (BP > 350°C)... 

Estimating the general nature of crude oils by measurement of two specific gravities. j... 

Specific gravity compared with H/C ratio for pure hydrocarbons. 

T being the boiling temperature (Kelvin) and S being tbe standard specific gravity (15.6°C/15.6°C). Refer to Chapter 4. 

In this manner, the KuQp of a petroieum cut can be calcuiated quickly from readily avkilable data, i. e., the specific gravity and the distillation curve. The A //np value is between 10 and 13 and defines the chemical nature of the cut as it will for the pure components. The characterization factor is extremely Va luable and widely used in refining although the discriminatory character of the Kuqp is less than that obtained by more modern physical methods described in 3.2 and 3.3. 

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. 

With the accumulation of results obtained from various and complex analyses of narrow cuts (Waterman method), correlations have been found f ctween refractive index, specific gravity and molecular weight on one hand, and percentages of paraffinic, naphthenic and aromatic carbon on the other. 

Group the component in a petroleum fraction, which is possible if the normal boiling temperature and the standard specific gravity are known. This method gives correct results when the chemical structure is simple as in the case of a paraffin or naphthene. 

The standard specific gravity can be estimated from using the followinc relation ... 

It is common that a mixture of hydrocarbons whose boiling points are far enough apart petroleum cut) is characterized by a distillation curve and an average standard specific gravity. It is then necessary to calculate the standard specific gravity of each fraction composing the cut by using the relation below [4.8] ... 

Riazi s method applies to fractions whose specific gravities are less than 0.97 and whose boiling points are less than 840 K. The Lee and Kesler method is applicable for fractions having molecular weights between 60 and 650. 

Using the principle of corresponding states requires knowledge of pseudo-critical constants of petroleum fractions these should be estimated starting from characteristic properties which are the normal boiling temperature and the standard specific gravity. 

For petroleum fractions, the values should be calculated starting with the standard specific gravity accor( ing to the relation ... 

K y = Watson characterization factor 5 = standard specific gravity... 

Maxwell and Bonnel (1955) proposed a method to calculate the vapor pressure of pure hydrocarbons or petroleum fractions whose normal boiling point and specific gravity are known. It is iterative if the boiling point is greater than 366.5 K ... 

Coefficients for converting an ASTM D 86 curve to an atmospheric flash curve[ and an application for a petroleum cut whose standard specific gravity isl 0.746. ... 

Calculation of the atmospheric TBP is rapid if it can be assumed that this distillation is ideal (which is not always the case in reality). It is only necessary to arrange the components in order of increasing boiling points and to accumulate the volumes determined by using the standard specific gravity. 

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