Date of publication: 2017-09-02 01:11
For fluids, the reference substance is usually the water, with a density of x 65 8 kg/m 8 at 9 degrees Celsius (water s densest temperature), used to determine whether or not the fluid will sink or float in water. In homework, this is usually assumed to be the reference substance when working with liquids.
Specific gravity is often abbreviated as sp gr. Specific gravity is also called relative density and is expressed by the formula:
Specific Gravity substance 66 ρ substance /ρ reference
Why would someone want to compare the density of a substance to the density of water? Let s look at one example. Salt water aquarium enthusiasts measure the amount of salt in their water by specific gravity where their reference material is fresh water.
The density of water is slugs/ft 8 at 89 o F ( 9 o C ). The specific weight in Imperial units is
The specific gravities of gases usually are compared to dry air which generally has a density of g per litre. The specific gravity of all other materials is compared to water as a fraction heavier lighter or heavier density.
The Specific Gravity of a gas is normally calculated with reference to air - and defined as the ratio of the density of the gas to the density of the air - at a specified temperature and pressure.
Now, considering that the density is calculated from mass and volume through the equation ρ 66 m / V , this means that if you took two substances of the same volume, the SG could be rewritten as a ratio of the their individual masses:
So if we wanted to find out the specific gravity of ethanol to water, and we know the weight of one gallon of water, then we would need to know the weight of one gallon of ethanol to complete the calculation. Or, alternately, if we knew the specific gravity of ethanol to water, and knew the weight of one gallon of water, we could use this last formula to find the weight of one gallon of ethanol.
The specific gravity of a substance is the ratio of its density to a specified reference substance. This ratio is a pure number, containing no units.
Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed.
There is a wide range of instruments designed to measure the specific gravity of a material. The hydrometer can be used to measure the specific gravity of any liquid. The device is designed to float freely at the liquid surface with a protruding stem giving a reading corresponding to the specific gravity of the liquid. Other instruments to measure specific gravity are the Pycnometer, and digital density meters based on oscillating U-tubes.