Joined: Aug 10, 2004 Posts: 881 Location: New Delhi-India
Posted: Thu Aug 04, 2005 9:39 pm Post subject:
Density = mass / volume
The density of water is 1 gram/cm3 since water was used as an early mass standard, one gram being informally defined as the mass of 1 cm3 of water.
Specific gravity is the weight ratio (expressed decimally) of two equal volumes of the substance and a standard
Specific Gravity = weight of substance /weight of equal volume of standard
--- water for solids and liquids
--- hydrogen or air for gases
So the specific gravity of water in our tanks is therefore the ratio of the density of that water at a specific temperature to the density of pure water at a specific temperature. It seems simple enough, but as we go further it gets more complicated.
The density of a substance is the volume that a certain mass occupies. Or, to put it another way, it is the mass of a certain volume of the substance.
Generally, as liquids and gases are heated they expand, and when they are cooled they contract. The density will therefore decrease with increasing temperature and increase with decreasing temperature.
So, if temperature affects density, does it also affect specific gravity.
So a floating glass hydrometer will give you the specific gravity reading, the specific gravity of natural seawater (S =35) is 1.0278 using the 3.98 Â°C standard. Also specific gravity of natural seawater can varry from region to region like Red sea comp. to Indian Ocean.
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