EDGE-TOOLS. (See CUTLERY and STEEL.) EGG. The ovum of birds and other oviparous animals. The changes which the hen's egg undergoes during incubation have been by Sir E. Home in the Philosophical Transactions for the year 1822, page 339, and illustrated by a beautiful series of plates after Bauer's drawings ; the same volume also contains a valuable paper by Dr. Prout on the same subject, but chiefly in reference to the chemical changes of the egg daring that process. The specific gravity of new-laid eggs at first rather exceeds that of water, varying from 1080 to 1090; but they soon become lighter, and swim on water, in consequence of evaporation through the pores of the shell. When an egg is boiled in water and suffered to cool in the air, it looses about 32 hund redths of a grain of saline matter, to= gether with a trace of animal matter and free alkali. The, mean weight of a hen's egg is about 875 grains, of which the shell and its inner membrane, weigh 93.7 grains, the albumen, or white, 529'8 grs.,
and the yolk 251.8 grs. The shell con tains about 2 per cent. of animal matter and 1 per cent. of the phosphates of lime and magnesia, the remainder being carbo nate of lime, with a trace of carbonate of magnesia. When the yolk of a haul boiled egg is digested in repeated por tions of strong alcohol, there remains a white residue having the leading charac ters of albumen, but containing phospho rus in some peculiar state of combina tion; the alcoholic solution is yellow, and deposits a crystalline fatty matter, and when distilled leaves a yellow oil. The albumen of the egg contains sulphur The use of the phosphorus is to yield phosphoric acid to form the bones of the chick ; but the source of the limo with which it is combined is not apparent, for it has not been detected in the soft parts of the egg, and hitherto no vascular com munication has been discovered between the chick and the shell.