ALBUMEN, an organic substance of a very complicated structure. It is typical of a group of bodies that have the same chemical composition but very different properties. The principal varieties are named albumen, fibrin, and casein. They are sometimes called the histo-genetic bodies, because they are essential to the building up of the animal organism. The vegetable kingdom is the original source of the albumenoid group of substances. In plants the albumen is found in greatest quantity in the seed. The mean average percentage composition of the albumenoids is as follows— [table]
The true chemical formula of these bodies is unknown, but if we regard the sulphur as replacing oxygen, then the simplest empirical formula is C 24 H 38 N 6 O 8....
All the albumenoid bodies are capable of existing in two forms— (a) soluble, (b ) insoluble. They belong to the class of bodies called colloids, and easily pass from the one condition into the other. Whether in the soluble or insoluble condition, they are easily dissolved by caustic potash, and may be precipitated by the addition of acetic acid. The soluble varieties are coagulated by alcohol, and precipitated by salts of copper, lead, and mercury. Strong sulphuric acid dissolves them, with the production of leucine, tyrosine, and ammoniacal salts. Strong nitric acid produces in their solutions a coagulum of a bright orange colour, and then gradually dissolves it with effervescence. A solution of nitrate of mercury, when heated with the members of the group, produces a deep red colour, and this is one of the most delicate tests. Some varieties of albumen coagulate when heated. All the albumenoid bodies are amorphous, and may be kept when dry for any length of time, but when moist they rapidly putrefy, and produce a sickening odour. Among the products of putrefaction are found leucine and tyrosine, and carbonate, butyrate, valerate, and sulphide of ammonium. The readiness with which these bodies change in the moist condition produces the digestive and other ferments in the body, and the synaptase, diastase, and emulsin which we find in plants. The special properties of albumen, fibrin, and casein will be described in the article Chemistry. From its property of coagulating when heated, albumen is employed in the arts to remove colouring matters from liquids.
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