Albumen

Albumen is a term used in Physiological Chemistry and in Botany in distinct senses: (a) A definite proteid substance (now frequently spelt Albumin, so as to agree in form with the other organic compounds), containing carbon, hydrogen, oxygen, nitrogen, and a small percentage of sulphur, coagulable by heat, mineral acids, alcohol, ether, tannic acid, &c., and existing in animals in white of egg and blood serum, and in plants in seeds and elsewhere (see ANIMAL CHEMISTRY, PROTEIDS). It is the sulphur of the albumen that blackens silver when brought in contact with eggs, and the smell of rotten eggs arises from the formation of sulphuretted hydrogen during their decomposition. The property of coagulating with heat at about 160° F. (71° C.) adapts albumen for the purpose of clarifying in sugar-refining and other processes. The albumen is added to the liquid in the cold state, allowed to mix thoroughly therein, and then, when heated, it coagulates, entangling and separating all the impurities suspended in the liquid. In cooking, the juiciness of a steak or roast depends largely on the proteid substances, coagulated by the sudden application of heat, preventing the evaporation of the juices of the meat during the subsequent slow heating required to fit it for the table. With many metallic salts, such as bichloride of mercury (corrosive sublimate), sulphate of copper (blue vitriol), acetate of lead (sugar of lead), and nitrate of silver (lunar caustic), it forms insoluble compounds, and is therefore used as an antidote to these poisons. A paste made by mixing albumen with slaked lime, sets, in a short time, to a mass of stony hardness, and, in virtue of this property, makes an admirable cement for broken earthenware, or other purposes. The importance of albumen as an article of diet will be discussed under FOOD. (b) A botanical term, without chemical significance, applied to the store of various reserve nutritive materials laid up for the use of the embryo within the seed. The term is only applied to the nutritive tissue when it is stored apart from the embryo proper, either within the embryo-sac (endosperm), or round about it (perisperm). Seeds which have abundant nutritive reserves containing proteids, &c., may still be 'exalbuminous' when the nutritive matter is stored within the embryo itself, as in the common pea. The characters of the albumen are important in botanical diagnosis. It is sometimes very small, as in the nettle; in other instances, on the contrary, it is very much larger than the embryo, as in the cocoa-nut, of which it forms the edible part. It is sometimes mealy or farinaceous, as in the cereals; oily, as in the poppy; horny, as in coffee; cartilaginous, as in the cocoa-nut; mucilaginous, as in the mallow. Vegetable ivory is the albumen of a palm (Phyttelephas) which grows on the banks of the Magdalena in Colombia, and is used in place of ivory. It is thus the albumen which makes many seeds valuable for edible and other purposes, though others, no less valuable, have the nutritive materials stored within the embryo. See OVULE, SEED.