Pyknometer

A pyknometer (also spelled pycnometer), also known as a specific gravity bottle, is a piece of laboratory glassware used to precisely measure the density or specific gravity of liquids and solids. It typically consists of a flask with a close-fitting ground glass stopper that has a capillary hole to allow air bubbles to escape, ensuring a consistent, known volume.

The measurement process involves weighing the empty pyknometer, then weighing it filled with a reference liquid (usually water), and finally weighing it filled with the test liquid. These weights enable calculation of the liquid’s relative density. Pyknometers are made from borosilicate glass for chemical resistance and thermal stability and are available in various standardized forms and sizes for different applications.

This instrument is used in scientific research, chemistry, and materials science to determine densities with high accuracy, complying with international standards such as ISO 3507. It requires careful cleaning and drying for precise measurements and is sometimes equipped with a ground-in thermometer for temperature-controlled tests.