Determination of Specific Gravity (Relative Density) of an oil sample

Relative density or specific density of oil is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water.

In an industrial environment, specific gravity is frequently used as an easy method to find out the concentration of different material solutions or to monitor the quality of polymer materials. It can also be used to assess physical alterations or measure the level of consistency among samples or lots.

Procedure for determining specific gravity of an oil sample

Equipment and apparatus

  • Balance machine
  • Hot air oven
  • Hot plate
  • Water bath
  • Pycnometer
  • Pipette
  • Sulfuric acid
  • n-Hexane
  • Ethanol
  • Deionized water


Pycnometer cleaning

  • Wash the pycnometer with soap solution using a brush to remove dirt.
  • Rinse the pycnometer with tap water.
  • Wash the stopper of the pycnometer with soap and rinse with tap water.
  • Now, we will wash the pycnometer with fuming sulfuric acid.
  • Take about 10ml of sulfuric acid into the pycnometer.
  • Attach the stopper and shake well.
  • Now, wait for 1 hour.
  • Now, we can see the sulfuric acid has turned yellowish. This is because all the remaining dirt is burnt out.
  • Pass sulfuric acid through the stopper channel to clear inner dirt.
  • Now, empty the pycnometer and wash with tap water carefully.
  • Finally, rinse the pycnometer with deionized water.


Pycnometer standardization

  • Take some cool distilled water in a beaker.
  • Heat the distilled water on a hot plate to boil.
  • After 15min of heating, remove the boiled distilled water from hot plate.
  • Now, fill the pycnometer with boiled distilled water.
  • Now, place the pycnometer into a water bath at 25℃ for 30min.
  • After 30min, take out from the water bath.
  • Adjust the water level at the proper point of the pycnometer, if needed.
  • Now, attach the stopper tightly.
  • Dry the outer surface properly with a dry cloth or tissue paper.
  • Now, take the weight of the water filled pycnometer.
  • Note the weight.
  • Discard the water from the pycnometer.
  • Rinse with 10ml ethanol to remove alcohol soluble dirt.
  • Again, rinse the pycnometer with 10ml n- Hexane to remove ether soluble dirt.
  • Now, dry the pycnometer in hot air oven at 100℃ for 15 minutes.
  • After drying, take out from the hot air oven and cool in desiccator.
  • Take the weight of the empty dry pycnometer and note the weight.


Filling pycnometer with oil sample

  • Now, fill with oil sample.
  • Place the pycnometer into a water bath at 25℃.
  • After 30 minutes, takeout from the water bath.
  • Now, attach the stopper tightly.
  • Dry and clear the outer surface of the pycnometer with dry tissue paper.
  • Now, take the weight of the oil filled pycnometer.
  • Note the weight.

Step-4 Calculation

Specific gravity formula

Formula for specific gravity calculation
Formula for specific gravity calculation


  • w2= empty pycnometer weight
  • w1= oil filled pycnometer weight
  • w3= water filled pycnometer weight

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Importance of determining specific gravity of an oil sample

Quality control:

When evaluating the consistency and quality of oil products, specific gravity is an essential consideration. It ensures conformance with the intended specifications through comparison against standards.

Calculating volume and mass:

Specific gravity is crucial for precise measurements in the manufacturing, trade, and transportation of oils since it is utilized to convert volume and mass.

Product characterization:

The specific gravities of various types of oil vary depending on their composition. The types and qualities of the oil samples can be identified with the use of these values.

Safety and compliance:

Specific gravity values are needed for some applications, such as those in the petrochemical and automotive sectors, in order to maintain safety standards and regulatory compliance.

Formulation of blends:

Specific gravity is used in industries that manufacture oil blends to determine the necessary amounts to achieve the desired qualities and attributes in the finished product.

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Sarmila K C

Welcome to The Science Notes! I'm Sarmila K C, a science writer with a background in Food Technology. My mission is to simplify complex scientific topics and make them accessible to everyone. I cover the various topics of science and explain them with clear, accurate information.

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