The Hot Chocolate Effect in Water and in Foam

Abstract

Frank S. Crawford’s application (1982) of the resonance in air model to find the speed of sound in liquids and foams in glass and ceramic cylinders is tested for water and albumen foam at different depths in a large beer mug. It is found, in contradiction of popular belief, that the model fails at most depths for water in a beer mug, but holds for the foam at all depths. No end correction is required and the velocity of sound in the albumen foam is that expected for a 90% air-filling fraction with water, and is density dependent.