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 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). Its density is 7.85 grams per cubic centimeter, or 7.85 kilograms per liter, or 7.85 metric tons per cubic meter. 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 gravity is the heaviness of a substance compared to that of water, and it is expressed without units. Also available in English translations.Specific Gravity And Viscosity Of Liquids Zarzycki,J (1982): Les Verres et l'état vitreux.Götze,W (2009): Complex Dynamics of glass forming liquids.This theory describes a slowing down of structural relaxation on cooling towards a critical temperature Tc, typically located 20% above Tg. The microscopic dynamics at low to moderate viscosities is addressed by a mode-coupling theory, developed by Wolfgang Götze and collaborators since the 1980s. More recently, the fragility has been quantitatively related to the details of the interatomic or intermolecular potential, and it has been shown that steeper interatomic potentials lead to more fragile liquids. Materials with a higher enthalpy of configuron formation compared with their enthalpy of motion have a higher Doremus fragility ratio, conversely melts with a relatively lower enthalpy of configuron formation have a lower fragility. Bond breaking modifies the properties of an amorphous material so that the higher the concentration of broken bonds termed configurons the lower the viscosity. Fragility is related to materials bond breaking processes caused by thermal fluctuations. Strong melts are those with (R D-1) < 1, whereas fragile melts are those with (R D-1) ≥ 1. The fragility of amorphous materials is numerically characterized by the Doremus’ fragility ratio R D=Q H/Q L. Amorphous materials are classified accordingly to the deviation from Arrhenius type behaviour of their viscosities as either strong when Q H-Q L
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