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 PI. 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 lower 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 riseSj 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, 



105185°— 18— Bull. 565 2 



