Knowledge Base
Why use specific gravity instead of density for liquid testing?
When it comes to liquids, specific gravity testing has a few big advantages. Wondering why it’s worth choosing specific gravity over density testing for liquids? Read on for our quick and simple guide.
The differences between specific gravity and density testing
With density testing, you are able to determine the weight of the liquid when it remains the same size. With specific gravity testing, which is sometimes also referred to as relative density testing, you are testing a liquid or substance and determining its weight against a control – the weight of water.
Density
Density is defined as mass per unit volume and has the SI unit kg m-3 or kg/m3. It can be determined to an absolute quantity.
Specific gravity
Specific gravity is the ratio of a material’s density with that of water at 60 degrees Fahrenheit or 4 degrees Celsius, which is the temperature at which water is most dense and is taken to have a value of 1.000 g/cm3. This makes specific gravity a relative quantity with no units.
Specific gravity testing divides the density of the substance by the density of water to determine its ratio.
Spotlighting the TQC Pressure Density Cup
Whether you’re planning to use specific gravity or density to test your liquids, the pressure density cup by TQC Sheen can help.
This VF2095 SG-cup has a fixed internal volume of 100 ml, which is condensed by the mechanism of the cup. It can be filled with a variety of liquids which will be rotated and agitated to remove air bubbles that may affect results. Density of the liquid is defined at a very high level of repeatability by weighing and it allows testing to recognized industry standard, EN ISO 2811-4.
Specific gravity measurements for common liquids
Our chart lists the specific gravity for some commonly used liquids.
| Liquid | Temperature in oC | Specific gravity |
| Acetic Acid | 25 | 1.052 |
| Acetone | 25 | 0.787 |
| Acetylene, liquid | 70oF | 0.38 |
| Creosote | 15 | 1.070 |
| Ethane | -89 | 0.572 |
| Ether | 25 | 0.716 |
| Glycerine (glycerol) | 25 | 1.263 |
| Mercury | 25 | 13.633 |
| Methyl acetate | 20 | 0.93 |
| Methyl iodide | 20 | 2.28 |
| Pentane-n | 15.6 | 0.631 |
| Propylene | 25 | 0.516 |
| Sodium chloride | 1.19 | |
| Sodium hydrate | 1.27 | |
| Sulphuric acid | 1.84 | |
| Turpentine | 25 | 0.871 |
Paint, coating and liquid testing at Industrial Physics
Our specialist paint and coating testing brand TQC Sheen offers a huge range of testing solutions, allowing you to accurately analyze paint, coatings, and general surface treatments across a whole range of applications. We have experience in a swathe of industries, from aerospace to pharmaceuticals, and our specialists are ready to help you find the testing solution you need. Have a browse of our featured TQC Sheen products.
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FAQs
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Specific gravity is the ratio of the density of a substance to the density of a reference substance, usually water.
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Specific gravity is easier to measure and compare, especially for liquids, and is temperature-independent.
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The specific gravity method is not only used for testing liquids. In fact, it can be used to test a huge range of materials, including plastics and polymers, rubber, ceramics and much more. It’s also a useful testing method for the construction industry and used to test cement, soils, aggregate, bitumen and pitch.
Curious about why density is so important when it comes to creating quality products? Check out our article explaining the relationship between density and quality when it comes to materials such as plastics, where calculating the strength to weight ratio is crucial.
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