Specific Gravity

Specific Gravity

Specific gravity is said to signify the ratio of the density of a substance. That is to the density of a reference substance. Specific density is also known as relative density. Let us learn more about SG here.

What is Specific Gravity?

It refers to the ratio of the mass of a substance to the mass of a reference substance at the same volume. Furthermore, apparent SG refers to the ratio of the weight of the volume of a substance to the weight of an equal volume of the reference substance.

Specific Gravity Formula

SG units are certainly not the same as for density. In other words, the formula for density is mass per unit volume. Contrary to that, the formula for SG is relatively different. The formula for SG is the density of the material under study divided by the water’s density. Most noteworthy, the SGequation is :
(mass of material ÷ volume of material) ÷ (mass of water ÷ volume of water)

Details of Specific Gravity

Specific gravity is a dimensionless quantity. Furthermore, it is independent of the systems of units used for measurements. This is because it is a ratio of densities.

Further, it varies with pressure and temperature. Substances which have an SG of 1 are neutrally buoyant in water. In contrast, substances which have an SG of greater than 1 are denser than water and may sink in it. Also, substances which have an SG of less than one are less dense than water. Hence, such substances would float on water.

The expression of the relationship of mass to volume is almost always in terms of the density of the substance under study. This takes place with scientific work involving SG.

The density of water shows variations with temperature and pressure. Similar is the case with the density of the sample. Therefore, it becomes necessary to specify the pressures and temperatures at which the determination of densities and weights takes place. The measurements almost always are made at 1 nominal atmosphere.

The variations due to pressure are probably neglected where specific gravity is measured. This is because; SG involves highly incompressible aqueous solutions or other incompressible substances.

The principal use of SG measurements is the determination of the concentrations of substances in aqueous solutions.

Furthermore, these are available in tables of SG versus concentration. Therefore, it becomes absolutely essential that the analyst enter the table with the correct form of SG.

An example can be the brewing industry. In the brewing industry, the Plato table lists the concentration of sucrose by weight against true SG.

Applications of Specific Gravity

It is certainly a concept that comes up in a variety of industrial applications. This is because it relates to fluid dynamics. An example can be when a mechanic shows how small plastic balls float in the transmission fluid. This is SG in action.

These industries may use the concept with a different reference substance than air or water. This certainly depends on the specific application in question.

Moreover, the application of earlier assumptions was to homework only. One must know what the SG is in reference to. This is essential when one is working on a real project. Most noteworthy, one must not make assumptions about it.

Solved Question for You

Q1 Which of the following is not related to SG?

A. Specific gravity varies with pressure and temperature
B. Specific gravity is a dimensionless quantity.
C. Specific gravity is a ratio of densities.
D. Specific gravity determines the rate of solubility of a substance

A1 The correct answer is option D.