Four Methods That Can Be Used to Find Specific Gravity
- Specific gravity can be calculated without measuring volume by utilizing a spring scale. The sample material is weighed in both water and air using this type of measurement. A sample formula for this measurement is: SG = W air / (W air - /W water) where W air is the weight of the material in air and W water is the weight of the material in water. This method of measurement is not good for sample materials that already float or have a specific gravity of less than 1 because the W water measurement becomes the negative force needed to keep the material underwater.
- When determining the specific gravity of a liquid, this measurement can be done using a hydrometer. A hydrometer is a bulb tube that has a constant cross-sectional area marked on the stalk. The hydrometer is floated first in a reference liquid, usually water. The displacement of the water is marked on the stalk. The hydrometer is then floated in the liquid of unknown density and the specific gravity is calculated using the difference in displacement.
- A pycnometer is a specific gravity bottle used to measure the relative density of a liquid. The specific density of the unknown liquid is calculated by weighing the pycnometer empty, full of water and full of the unknown liquid. The specific density of the unknown liquid is determined by examining the weight difference between the known liquid, generally water, and the weight of the unknown liquid in relation to the weight of the empty flask.
- The specific gravity can easily be determined by using a simple formula: SG = substance/reference where substance is the density of the substance being measured and reference denotes the density of the reference sample, usually water. In this calculation where the reference is water, it is assumed to be measured at 3.98 degrees Celsius, the temperature where water is most dense at 1000kg/m3.
