The Collaborative International Dictionary of English v.0.48:

Nitrometer \Ni*trom"e*ter\, n. [Nitro- + -meter: cf. F.
   nitrom[`e]tre.] (Chem.)
   An apparatus for determining the amount of nitrogen or some
   of its compounds in any substance subjected to analysis; an
   azotometer.
   [1913 Webster]