The Collaborative International Dictionary of English v.0.48:

Effervescence \Ef`fer*ves"cence\, Effervescency
\Ef`fer*ves"cen*cy\, n. [Cf. F. effervescence.]
   A kind of natural ebullition; that commotion of a fluid which
   takes place when some part of the mass flies off in a gaseous
   form, producing innumerable small bubbles; as, the
   effervescence of a carbonate with citric acid.
   [1913 Webster]

WordNet (r) 3.0 (2006):

effervescence
    n 1: the process of bubbling as gas escapes
    2: the property of giving off bubbles [syn: bubbliness,
       effervescence, frothiness]