eudiometer

/ˌjuːdiˈɑːmɪtər/
noun
  1. A scientific instrument used to measure the volume or change in volume of gases during a chemical reaction.
    • The chemistry student used a eudiometer to measure the oxygen produced by the reaction.
    • Early scientists relied on the eudiometer to analyze the composition of air.
    • In the lab, the eudiometer was carefully filled with water to trap the gas sample.