Pycnometers are glass or metal containers with a determined volume. Typically, they are used to determine the density of liquids and their dispersions. Density and dispersion can be measured by weighing the defined volumes of powders and granules. Pycnometers can also be used to determine the density of the solid phase in porous solids. To determine the density of a porous solid, a sample must first be crushed, ground, or powdered to the point that all pores are opened. Pycnometers can then be used. Fast, full automatic analyzers can be used to provide high-speed, high-precision measurements and density calculations on a variety of materials.
Pycnometers can be used with solids, liquids, or gases by way of either a glass assembly or digital technology. Glass assembly pycnometers use M1 and M2 measurements. The M1 measurement initially weighs glass pycnometers of defined volume without a sample. M2 measurements are taken when the glass pycnometers are filled with a sample and re-weighed. The difference between M1 and M2 technologies is divided by the volume of the beaker. Digital pycnometers vary in terms of output and mounting styles, and are available in benchtop models. They often come with their own sample cells coordinated to work with the pycnometer.
Pycnometers carry specifications for measuring range and accuracy. The sample cell volume and the operating pressure range are additional specifications to consider when choosing pycnometers. Features for pycnometers may include data storage or automatic calibration. Pycnometers can also have integral temperature sensors and can compensate for changes in temperature.
Interface and display options are additional features to consider when selecting pycnometers. Interfaces for pycnometers are available in analog designs with knobs, switches, and dials; digital models with local keypads and menus; or are computer-controlled via serial, parallel, or other interfaces. Display choices for pycnometers include:
- analog meters
- numeric or alphanumeric digital displays or videos
- cathode ray tube (CRT)
- liquid crystal display (LCD)
Another option is to have no local display at all, but to have the data gathered by another instrument. Likewise, the user controls for pycnometers can also be analog or digital or can be operated through a host computer.