The Collaborative International Dictionary of English v.0.48:

Demephitize \De*meph"i*tize\, v. t. [imp. & p. p.
   Demephitized; p. pr. & vb. n. Demephitizing.] [Cf. F.
   m['e]phitiser to infect with mephitis.]
   To purify from mephitic or foul air. --
   De*meph`i*ti*za"tion, n.
   [1913 Webster]