an intestine motion excited among the parts of two bodies of different natures, when they reciprocally dissolve each other. Effervescences are commonly attended with bubbles, vapours, small jets of the liquid, and a hissing noise; which phenomena again are occasioned by the air disengaging itself. Sometimes also they are accompanied with a great degree of heat, from the decomposition of some substances and the formation of new compounds.

Formerly the word fermentation was also applied to effervescences; but now that word is confined to the motion naturally excited in animal and vegetable matters, and from which new combinations among their principles take place.