|MadSci Network: Chemistry|
Dear Jennifer, The appropriate instrument to measure specific gravity of powders, especially if they float on water, is a GAS PYCNOMETER. It works along the same principles of volume displacement, as a liquid pycnometer, although the gas pressure has to be controlled. Such instruments are commercially available at various degrees of automation (see e.g. http://micromeritics.com/catalog_index.html). Probably a manual instrument (Beckman) is to be found in a corner of a cupboard of any powder analysis lab. Another possibility, if urgency prevails over accuracy, is to use an ordinary pycnometer (glass vial) filled with a low-density liquid (methanol, heptane, "Isopar G"..) instead of water. Some skill is needed due to the volatility of these liquids. Their density is also very temperature-dependent. Best Regards Werner Sieber
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