HOW TO CANDLE EGGS. 7 
should be taken into consideration when comparing the illustrations 
and descriptions with the appearance of eggs before the candle- 
Candling will enable one to identify cracked eggs more accurately 
than will clicking. Therefore, when eggs are graded by candling 
to judge the quality of the contents, those with damaged shells can 
be removed at the same time. If there are a few small holes in the 
candle to shed light on the egg container below, dirty eggs can be 
picked out with but one handling of the eggs. Eggs with mold 
growing in the cracks are detected to some extent by candling, but 
much more readily away from the candle. (See PL IV, fig. 2.) 
THE AIR SPACE. 
The air space of a fresh egg is less than three-fourths inch in 
diameter, as may be seen by tilting an egg with the large end in 
front of a candle. As 'the egg ages the air space increases in size, 
owing to the evaporation of water from the liquid contents. The 
amount of evaporation depends very largely upon the age of the egg 
and the temperature at which it has been kept. In winter and spring 
eggs shrink more slowly than in summer. Therefore, the early spring 
eggs on the market will have smaller air spaces than the summer 
eggs. With continued shrinkage the egg membrane pulls away from 
the shell membrane at the air space, so that when the egg is turned 
before the candle the lower wall of the air cell changes at the same 
time. This condition is shown in Plate XI. In grading an egg the 
size of the air space is useful in determining its freshness. For ex- 
ample, a full egg will be graded as a " first " and a shrunken egg as 
a " second." Most bad eggs have enlarged air cells. The variations 
in the size of the air space of eggs of different grades are shown in 
Plates I and XII. 
The egg membrane, which forms the low T er wall of the air cell, 
may become broken by jars or jolts during the haul to market, or by 
severe shaking in the hand or other rough handling. When this 
membrane is broken the air cell always rises, irrespective of the 
position in which the egg is held, as may be seen from Plate IV. 
figure 1. Small bubbles of air frequently are seen when the egg is 
turned before the candle. When an egg becomes very stale the air 
in the air cell may move all the way around the egg between the 
two membranes. Such an air cell is termed "movable." Eggs with 
broken and movable air cells are graded as " seconds," if otherwise 
good, even though they may show no shrinkage. 
THE WHITE. 
The two factors to be considered when studying the white of an 
egg before the candle are its firmness and its color. A firm, thick 
white is found in a fresh egg. and a weak, thin white in a stale egg 7 
105185°— 18— Bull. 565 2 
