Title: Determination of Weight Per Millilitre and Relative Density (Specific Gravity)
- Objective: To determine the Weight per ml and Relative Density of the solutions and solvents.
- Principle: The Weight per millilitre is determined by dividing fill weight of test liquid in gram by the capacity of pycnometer expressed in ml at the specified temperature.
3. Procedure:
3.1 Definitions:
- Specific Gravity: It is based on the ratio of the weight of a liquid in air at 25oC to that of an equal volume of water at the same temperature. Where a temperature is specified in the individual monograph, the Specific Gravity is the ratio of the weight of a liquid in air at specified temperature to that of an equal volume of water at the same temperature.
- Relative Density: It is defined as the mass of a unit volume of the substance at 25oC expressed in g, of the quantity of liquid that fills a pycnometer at the specified temperature to that of an equal volume of water at the same temperature.
- Method: (Weight per ml)
Select a thoroughly clean and dry pycnometer that previously has been calibrated by determining its weight and the weight of recently boiled and cooled water contained in it at 25°C. Adjust the temperature of the test liquid to about 20°C and fill the pycnometer with it. Adjust the temperature of the filled pycnometer to 25°C, remove any excess liquid, and weigh. When the monograph specifies a temperature different from 25°C, filled pycnometers must be brought to the temperature of the balance before they are weighed. Subtract the tare weight of the pycnometer from the filled weight of the pycnometer.
Determine the weight per ml by dividing the weight of test liquid in gram by the capacity of pycnometer expressed in ml at the specified temperature.
- Method: (Relative Density)
Proceed as described under weight per millilitre method. Divide the weight of the substance in the pycnometer by the weight of water contained in the pycnometer, both determined at 25°C, unless otherwise specified in the individual monograph.