The pyknometer (from Greek: πυκνός (puknos) meaning "dense"), also called pycnometer or specific gravity bottle, is a flask, usually made of glass, with a close-fitting ground glass stopper with a capillary tube through it, so that air bubbles may escape from the apparatus. This enables the density of a fluid to be measured accurately, by reference to an appropriate working fluid such as water or mercury, using an analytical balance.
If the flask is weighed empty, full of water, and full of a liquid whose specific gravity is desired, the specific gravity of the liquid can easily be calculated. The particle density of a powder, to which the usual method of weighing cannot be applied, can also be determined with a pyknometer. The powder is added to the pyknometer, which is then weighed, giving the weight of the powder sample. The pyknometer is then filled with a liquid of known density, in which the powder is completely insoluble. The weight of the displaced liquid can then be determined, and hence the specific gravity of the powder.
The pyknometer is used in ISO standard: ISO 1183-1:2004, and ASTM standard: ASTM D854.
An empty glass pyknometer and stopper
- Pycnometer full.jpg
A full Pyknometer
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