volatilization gravimetry
/ vol-uh-til-ih-ZAY-shun /
Imagine weighing a wet sponge, baking out all the water, weighing the dry sponge, and learning how much water was inside simply from how much lighter it got. Volatilization gravimetry uses exactly that 'measure by what leaves' idea.
Volatilization gravimetry determines an analyte by driving it off as a gas — through heating or chemical reaction — and measuring a mass change. You can weigh the loss from the sample (the indirect way) or trap the released gas in an absorbent and weigh the gain (the direct way).
It matters because some analytes are far easier to remove as a gas than to precipitate as a solid: water, carbon dioxide from carbonates, or moisture in a food sample. The honest caveat is that you must be sure only the intended species leaves, or the mass change tells the wrong story.
To measure the water in a hydrated salt, you weigh it, heat it until all the water of crystallization escapes, and weigh again; the mass lost is the mass of water.
Measure the analyte by the mass that leaves as a gas.
The direct (trap-and-weigh) version is usually more reliable than the indirect (weigh-the-loss) version, because trapping confirms what actually left, whereas a loss could include any unintended volatile component.