102 THE DOMESTIC FOWL. 



This air bag is of such great importance to the de- 

 velopment of the chick, probably by supplying it with 

 a limited atmosphere of oxygen, that if the blunt end 

 of an egg be pierced with the point of the smallest 

 needle the egg cannot be hatched, but perishes. 



From the air bag being thus placed at the blunt end 

 of the egg, important signs may be taken to distin- 

 guish the freshness of an egg ; for, as the air in the cell 

 will not abstract heat from without, like a more solid 

 substance, it is a usual practice to apply the tonguo 

 to the blunt end of an egg, and if it feels rather warm, 

 it is stale, but if cold, it is fresh. This, however, is 

 a much more uncertain test than the comparative size 

 of the small circle seen by the transmitted light of a 

 candle or otherwise, a small circle being a proof of 

 freshness, and a large one of staleness. 



The shell of an egg, chemically speaking, consists 

 chiefly of carbonate of lime, similar to chalk, with a 

 small quantity of phosphate of lime and animal mucus. 

 When burnt, the animal matter and the carbonic acid 

 gas of the carbonate of lime are separated, the first 

 being reduced to ashes or animal charcoal, while the 

 second is dissipated, leaving the decarbonised lime 

 mixed with a little phosphate of lime. 



The white of the egg, (albumen,) is without taste or 

 smell, of a viscid, glairy consistence, readily dissolving 

 in water, coagulable by acids, by spirits of wine, and by 

 a temperature of 165 F. If it has once been coagulat- 

 ed, it is no longer soluble either in cold or hot water, 

 and acquires a slight insipid taste. Experiments show 

 that it is composed of 80 parts of water, 15^ parts of 

 albumen, and 4J parts of mucus, besides giving traces 

 of soda, benzoic acid, and sulphuretted hydrogen gas. 



The yolk has an insipid, bland, oily taste, and when 

 agitated with water, forms a milky emulsion. If it be 

 long boiled, it becomes a granular, friable solid, yield- 

 ing upon expression a yellow, insipid, fixed oil. It 

 consists, chemically, of water, oil, albumen, and gela- 



