in a humid refrigerator loses 4 milligrams of
water to evaporation each day. The cook can
use this moisture loss to estimate the
freshness of an egg. A new egg with an air
space less than ^1 / 8 inch/3 mm deep is denser
than water and will sink to the bottom of a
bowl of water. As an egg ages and its air cell
expands, it gets progressively less dense, and
the wide end of the egg rises higher and
higher in the water. An egg that actually floats
is very old and should be discarded. Around
1750, the English cookbook author Hannah
Glasse gave two ways of determining the
freshness of an egg, an important talent at a
time when it might have been sitting for some
time in an odd corner of the yard. One is to
feel how warm it is — probably less than
reliable — but the second indirectly assays
the air cell: “[Another way] to know a good
egg, is to put the egg into a pan of cold water;
the fresher the egg the sooner it will fall to the
bottom; if rotten, it will swim at the top.”