What Is a Pycnometer?
A pycnometer is a glass appliance that measures the specific gravity of a liquid. Also included are pycnometers that can be used to measure solid powders.
- A pycnometer is a device that can accurately measure the volume of a glass or metal container. It measures the volume defined by the density and volume of a liquid by simple weighing. Use the known volume of a pycnometer to determine the density of powder, liquid, and particulates. [1]
- If the test temperature exceeds the temperature corresponding to the known pycnometer volume by 5 ° C, the density shall be corrected for changes in the pycnometer volume.
- Under test conditions, the volume V t of the pycnometer is calculated by the following formula, expressed in milliliters (mL), and the calculation involves 5 important parameters.
- V t = Vc [1 + P (t T -t C )]
- In the formula:
Vcthe volume of the pycnometer at the calibration temperature tC, the unit is milliliter (mL);
t T test temperature in degrees Celsius ();
t C corrected temperature in degrees Celsius ();
P the coefficient of volume expansion, the reciprocal of Celsius (° C), which is related to the material of the pycnometer (see Table 1). [2]
- The pycnometer must be clean and dry (the attached thermometer cannot be heated and dried).
- Pycnometer
The pycnometer filled with the test solution must be cleaned. If the test product is an oil, it should be poured as much as possible after the measurement. The stopper can be rinsed with petroleum ether and chloroform several times before the oil is completely washed, and then ethanol 2. Rinse thoroughly with water and measure the weight of water according to law.
- For the test product and water bottling, care should be taken to pour the inside of the specific gravity bottle along the wall to avoid air bubbles. If there are air bubbles, they should be left for a while until the air bubbles disappear and then the temperature is measured and weighed. If the test product is a cat thick liquid such as syrup, glycerin, etc., it should be poured slowly along the wall when bottling. The bubbles produced by the thick consistency are difficult to escape and affect the measurement results.
- When taking the pycnometer out of the water bath, use your fingers to hold the bottleneck, but not the belly of the bottle, so as to prevent the liquid from expanding and overflowing due to the temperature of the hand.
- When measuring corrosive test articles, in order to avoid corrosion of the balance pan, a watch glass can be placed on the balance pan during weighing, and then placed in a pycnometer for weighing.
- When the room temperature is higher than 20.9 ° C or the temperature specified under each variety, it must be managed to adjust the ambient temperature to slightly lower than the specified temperature. Otherwise, it is easy to cause the liquid in the pycnometer, which is balanced at the specified temperature, to swell and overflow due to environmental frustration higher than the specified temperature during the weighing process, leading to errors. [3-4]