Ovi Albumen. Egg Albumen. Ovi Vitellus. Yolk of Egg.
Synonyms.—Albumen; White of Egg.
Egg albumen is the liquid white of the egg of Gallus Bankiva, var. domesticus (Order Gallinae). It occurs as a glairy, viscid, usually colourless, but occasionally pale yellow, liquid; almost tasteless, or having only a faint saline taste; soluble in water, but insoluble in alcohol or ether. It consists of a semi-fluid material, which is pervaded by a network of firmer and more fibrous nature, closely resembling the membrane enclosing the vitreous humour of the eye. On heating the aqueous solution to 75° it becomes coagulated. It is precipitated by most mineral and some organic acids, but not by phosphoric or acetic acid. Alcohol coagulates it, and ether precipitates it, the precipitate being only partially soluble in water. It is soluble in caustic alkalies, but forms precipitates with the salts of most of the heavy metals, e.g., mercury, copper, etc. It is precipitated also by volatile oils, camphor, phenol, and tannic acid. Its aqueous solution is laevorotatory. When allowed to putrefy, it gives rise not only to amino-acids but also to other aromatic and fatty acids (e.g., butyric acid), indol, skatole, and cresol, and also to the alkaloid-like ptomaines. Egg albumen should be free from any unpleasant odour. Albumen Siccum, or dried albumen, may be obtained by careful evaporation on glass plates at a temperature not above 50°. It occurs in yellowish, transparent flakes or scales of a horny consistence. It is nearly soluble in about 10 parts of water, forming a neutral solution, which should respond generally to the description and tests given above. It should be free from unpleasant odour or taste.
Constituents.—The semi-fluid portion of egg albumen is alkaline, and contains 82 to 88 per cent. of water, about 12 per cent. of proteins (globulins and albumins), 0.5 per cent. of sugar, traces of fats, alkaline soaps, lecithin and cholesterol, and less than 1 per cent. of inorganic residue. The total average weight for one egg is 24 grammes (371 grains). On complete incineration, it yields on an average about 0.65 per cent. of ash, which consists of 42 per cent. of potassium chloride, 9 per cent. of sodium chloride, phosphates and sulphates of the alkalies, together with some silica, lime, iron, and magnesium. The organic portion has the elementary composition, carbon 53.7 per cent., nitrogen 15.5 per cent., hydrogen 7.1 per cent., oxygen 22.1 per cent., sulphur 1.6 per cent. The manner in which sulphur is contained in the molecule is unknown; its presence may be shown, however, by boiling the egg albumen with an alkaline solution of lead oxide, when lead sulphide is formed. By the action of the gastric juice, or pepsin in very dilute hydrochloric acid, albumen is converted into acid-albumin or syntonin, and finally into peptone. Solution of egg albumen is prepared by mixing egg albumen by trituration with four times its volume of distilled water, and filtering through clean tow, previously moistened with distilled water; it should be recently prepared.
Uses.—Solution of egg albumen with boric acid is sometimes used as a dressing in surgery. A solution of egg albumen made by dissolving the white of one egg in 150 mils (5 fluid ounces) of boiled and cooled water, adding salt to taste, and a little brand if necessary, is used in the diarrhoea of infants.
YOLK OF EGG.
Yolk of egg is obtained from the egg of Gallus Bankiva var. domesticus (Order Gallinae). The yolk of the egg is a membranous sac, enclosing a yellow, or reddish-yellow, opaque, odourless liquid, with a bland taste and alkaline reaction. The liquid is a natural emulsion of a yellow oil, which is suspended in water by the aid of albuminous matter.
Constituents.—It contains about 16 per cent. of vitellin and other proteins, 11 per cent. of lecithin, and 23 per cent. of fats.
Uses.—Yolk of egg is employed as an emulsifying agent for oils, being particularly useful in the case of oil of turpentine and other limpid volatile oils. For this purpose it should be triturated lightly in a mortar, the oil being added by degrees, with a little water if necessary. One yolk will, as a rule, emulsify 3 to 4 fluid ounces of fixed oil. (See Emulsiones.)