eudiometer
    n 1: measuring instrument consisting of a graduated glass tube
         for measuring volume changes in chemical reactions between
         gases

Eudiometer \Eu`di*om"e*ter\, n. [Gr. ? fair, clear weather, fr.
   ? fine, clear ( said of the air or weather) + -meter: cf. F.
   ediom[`e]tre.] (Chem.)
   An instrument for the volumetric measurement of gases; -- so
   named because frequently used to determine the purity of the
   air.
   [1913 Webster]

   Note: It usually consists of a finely graduated and
         calibrated glass tube, open at one end, the bottom; and
         having near the top a pair of platinum wires fused in,
         to allow the passage of an electric spark, as the
         process involves the explosion and combustion of one of
         the ingredients to be determined. The operation is
         conducted in a trough of mercury, or sometimes over
         water. Cf. Burette. Ure's eudiometer has the tube
         bent in the form of the letter. U. Eudiometric