INTRODUCTION :
Specific gravity is based on the ratio of the ‘weight of the substance in air at 25°C to that of an equal volume of water at the same temperature. Unless otherwise stated in the individual testing procedure, the specific gravity determination is applicable only to liquids.
Where a temperature is specified in the individual testing procedure, the specific gravity is the ratio of the weight of the substance in air at the specified temperature to that of an 'equal volume of water at the same temperature.
When the substance is a solid at 25°C, determine the specific gravity at the temperature directed in the individual testing procedure, and refer to water at 25°C.
PROCEDURE :
Remove the Pycnometer lid.
Dry the pycnometer at 105°C for about 1 hour and then cool in a desiccator for about 30 minutes.
Take the weight of empty pycnometer (W1 g).
Fill the pycnometer with recently boiled and cooled purified water at about 20°C.
Adjust the temperature of the filled pycnometer to 25°C.
Remove any excess of water by wiping with tissue paper and take the weight accurately (W2 g).
Discard the water and dry the pycnometer at 105°C for about 1 hour and cool in a desiccator for about 30 minutes.
Adjust the temperature of the sample to about 20°C.
Fill the pycnometer with the sample.
Adjust the temperature of the filled pycnometer to 25°C.
Remove any excess of sample and take the weight accurately (W3 g) at 25 °C.
Calculation :
W3 - W1
Specific gravity of the sample = ----------------
W2 - W1
Specific gravity, general testing procedure, temperature, testing procedure
