places on the wall. This is because the contact angle at a glass
surface is so small (in fact it is zero) that the Laplace pressure in the
air is positive, and an air pocket will thus disappear; see Figure
14.10c. However, a few crevices may be contaminated with lipid
material, which would greatly increase the contact angle and hence
allow the retention of an air pocket.Besides bread and cake, in which yeast or baking soda is used to
obtain gas cells, other baked products have gas inclusions without CO 2
FIGURE14.10 Gas pockets in a liquid. G is a gas, W is water, and hatching
indicates a solid. (a) Formation of a persistent air bubble due to adsorbed
hydrophobic particles and dissolution of most of the air. (b) Growth of a gas pocket
if the contact angle, as measured in the water phase, is large and the water is
supersaturated with the gas, and subsequent formation and dislodgement of a
bubble. (c) Disappearance of a gas pocket in a crevice if the contact angle is small.