THE SPECIFIC GRAVITY

 Specific Gravity

The Specific gravity is the diagnostic property of minerals or any substance that may be define as the ratio of densities.

The ratio of density of solid or liquid to standard fluid at particular temperature and particular pressure.

                                            Or

This is the comparison between two substance`s densities. In specific gravity we need a standard thing or substance for better comparison results. Sp. gr. in gases we can take dry air for standard at particular temperature or pressure or in fluid or solid cases we can compare with water (1gm/ml) at 4°C. 

Why 4°C ?

Because at this temperature water has maximum density.

 

    Density            

         Mass(kg) per unit Volume(m³).

                 = Mass/Volume & Unit = kg/m³

                           

A standard jar has vol. (1*1*1) = 1 m³

           

        Some important densities:

             Water density 1000 kg/m3 

    = 1000 kg/1000 litre at 4°c temp.

    = 1.0 gm/ml or 1.0 gm/cm³ at 4°c temp.

        Air density        1.22kg/m³

        Sand density    1840 kg/m³

        Gold density    19300 kg/m³

        Cement density    1440 kg/m³

        Wood density    1200 kg/m3

        PCC Concrete        2400 kg/m³

        RCC Concrete        2500 kg/m³

        Steel density        7850 kg/m³

        Pure Petrol        760 kg/m³

        Mercury        13600 kg/m³

         

        Thus

        The specific gravity (sp. gr.)

In simply we can say that ratio of density of fluid to density of water at standard temperature (4 °c).

Or

Ratio of density of gas to dry air at standard temperature and pressure.

 

Specific gravity is also known as Relative gravity. it is the dimensionless quantity.

 

Specific gravity = Density of substance/Density of reference

 

  Example 1 : To find the specific gravity of mercury ?

  We know density of mercury is 13600 kg/m³

         = 13600 kg/m3 /1000 kg/m³

          Sp. gr. of mercury= 13.6

    That means mercury is 13.6 times heavy than water because water has sp. gravity is 1.0 g/cm³ or 1000 kg/m^3. If material have specific gravity less than 1 g/cm3 then it will be float on water and its vice-versa.

  Example 2: if the specific gravity of mercury is 13.6 then find the mercury density ?

                        Sp. gr. = 13.6

      Density = Sp. gr. * density of reference fluid

            = 13.6*1000

          Density = 13600 kg/m³ 

 

    Specific gravity of some important minerals:

    Quartz                 2.65

    Gold                    19.3        

    Pyrite                   5.0   

Gold sp. gr. 19.3

Pyrite sp. gr.  5

    Galena                 7.5

    Calcite                 2.60

    Fluorite                3.18

    Hematite              5.2

    Felspar                2.6

   Chalcopyrite         4.2    

  

Instruments

1) Walker`s Steel Yard

2) Jolly`s Spring Balance

3) The Beam Balance