![]() Although specific gravity is still frequently used, this traditional term is not used under the SI system it has been replaced by “relative density. Specific gravity for liquids is nearly always measured with respect to water at its densest (at 4 C or 39.2 F) for gases, the reference is air at room. By convention, specific gravities of all gases at all pressures are usually set equal to the ratio of the molecular weight of the gas to that of air (28.967). The ideal gas laws can be used to show that the specific gravity (ratio of densities) is also equal to the ratio of the molecular weights. However, slightly different standards are sometimes used in different locations and in different units. The standard temperature is usually 60☏, and the standard pressure is usually 14.696 psia. The specific gravity of a gas, γ, is the ratio of the density of the gas at standard pressure and temperature to the density of air at the same standard pressure and temperature. ΡH2O = density of water – normally at temperature 4 oC Ρsubstance = density of the fluid or substance At a specified temperature and can be expressed as As a rule of thumb, multiply the specific gravity of a liquid by 8.34 to find the weight of a gallon of that liquid.Specific Gravity (Relative Density) SG also called relative density that is ratio of the density of a substance to that of a standard substance. In our table below, we have given various liquids' characteristics with the temperature modified to one of more of a real world value. You can observe the little balls floating in the tube. Another version will determine the concentration of anti-freeze in an automobile radiator. This is the same instrument that we use to tell if your automobile battery is fully charged. The float is calibrated to float on fresh water so if the fluid you are testing has a higher specific gravity, the float will raise in the liquid and at a lower specific gravity it will sink lower in the liquid. It consist of a glass cylinder with a rubber bulb on top, and a float positioned inside the glass tube. We measure specific gravity with a hydrometer. The really important thing to keep in mind is that there is no correlation between viscosity and specific gravity. Like specific gravity, viscosity can be altered by a change in temperature, but unlike specific gravity it can also be altered by agitation. Thick liquids are said to have a high viscosity and thin liquids a low viscosity. It is important that you do not confuse specific gravity with viscosity which is a measurement of a fluids resistance to pouring, though there is often what is perceived to be an obvious relationship. As you have already guessed fresh water at 4☌ (39° F) has been assigned a value of one (1). If it sinks into the fresh water the specific gravity is more than one. If the liquid you are comparing will float on this water it has a specific gravity of less than one (1). In the SI system, specific weight of water at 4☌ will be: 1000 kg/m3 9.807 m/s2 9807 kg/ (m2 s2) 9807 N/m3 9. ![]() In relationship to liquids, the term specific gravity is used to describe the weight or density of a liquid compared to an equal volume of fresh water at 4☌ (39° F). When the specific gravity ratio for a given material is greater. If the specific gravity ratio for a given substance is less than 1, that means the material will float in the reference substance. ![]() This ratio is a pure number, containing no units. Its density is 7.85 grams per cubic centimeter, or 7.85 kilograms per liter, or 7.85 metric tons per cubic meter. The specific gravity of a substance is the ratio of its density to a specified reference substance. If something is 7.85 times as heavy as an equal volume of water (such as iron is) its specific gravity is 7.85. ![]() In the metric system specific gravity is the same as in the English system. Specific density is the ratio of density of the substance to the density of water at 4C. Specific gravity is the heaviness of a substance compared to that of water, and it is expressed without units. Specific Gravity And Viscosity Of Liquids
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