Damage to eggs by heating and consequent financial loss is inexcusable.  In the first place, market eggs have no business being fertilized, but whether they are or not they should be kept in a place sufficiently cool to prevent all germ growth.

The egg shell is porous so that the developing chick may obtain air.  This exposes the moist contents of the egg to the drying influence of the atmosphere.  Evaporation from eggs takes place constantly.  It is increased by warm temperatures, dry air and currents of air striking the egg.

When the egg is formed within the hen the contents fill the shell completely.  As the egg cools the contents shrink, and the two layers of membrane separate in the large end of the egg, causing the appearance of the bubble or air cell.  Evaporation of water from the egg further shrinks the contents and increases the size of the air cell.  The size of the air cell is commonly taken as a guide to the age of the egg.  But when we consider that with the same relative humidity on a hot July day, evaporation would take place about ten times as fast as on a frosty November morning, and that differences in humidity and air currents equally great occur between localities, we see that the age of an egg, judged by this method, means simply the extent of evaporation, and proves nothing at all about the actual age.

Even as a measure of evaporation, the size of the air cell may be deceptive, for when an egg with an air cell of considerable size is roughly handled, the air cell breaks down the side of the egg, and gives the air cell the appearance of being larger than it really is.  Still rougher handling of shrunken eggs may cause the rupture of the inner membrane, allowing the air to escape into the contents of the egg.  This causes a so-called watery or frothy egg.  The quality is in no wise injured by the mechanical mishap, but eggs so ruptured are usually discriminated against by candlers.

In this connection it might be well to speak further of the subject of “white strength,” by which is meant the stiffness or viscosity of the egg white.  The white of an egg is a limpid, clear liquid, but in the egg of good quality that portion immediately surrounding the yolk appears to be in a semi-solid mass.  The cause of this appearance is the presence of an invisible network of fibrous material.  By age and mechanical disturbance this network is gradually broken down and the liquid white separates out.  Such a weak and watery white is usually associated with shrunken eggs.  These eggs will not stand up well or whip into a firm froth and are thrown in lower grades.

The weakness of the yolk membranes also increases with age, and is objectionable because the breakage of the yolk is unsightly and spoils the egg for poaching.

The shrunken egg is most abundant in the fall, when the rising prices tempt the farmer and grocery man to hold the eggs.  This holding is so prevalent, in fact, that from August to December full fresh eggs are the exception rather than the rule.