ALBUMEN or ALBUMIN. (E•e., albumen, the white of an egg.) Albumen, nn organic nutritive principle, is a constitnent of all animal fluids and solids. The white of eggs contains 12 per cent. of albumen, and the fluid portion of blood, or serum, 7 per cent. It occurs also in the flesh, in the brain, and more or less in rill serous fluids. Fibrin also may be regarded as coagulated albumen. It occurs in the vegetable kingdom, in the sap or juice of many plants, such as the potato, turnip, carrot, &c., in the seeds of the cereal grasses, and in many nuts.
Albumen exists in two different modifications—soluble and insoluble albumen. It is in the former modification that it occurs in the animal body, but the insoluble modification may readily be prepared from the soluble one by the action of heat. This property of becoming insoluble or coagulating, as it is termed, by the action of heat, is especially characteristic of this substance.
Albumen contains carbon, hydrogen, oxygen, and nitrogen, together with traces of sulphur and phosphorus. Its chemical composition is as follows :— Animal albumen is always associated with certain inorganic salts and free soda. It exists in the animal body in solution, in the form of an alkaline albuminate. If the white of eggs, or the serum of blood, or any animal liquid containiug albumen be incinerated, the residue is chiefly carbonate of soda,. This alkali may readily be removed, and the albumen rendered insoluble, or coagulated, by the action of heat. Exposed to a gentle heat, soluble albumen gives off a pecu liar, characteristic odour. On raising the heat to 54° (130° F.), white fibres of insoluble albumen begin to appear ; st 70° (160° F.) it becomes a solid, jelly-like mass, and at 100° (212° F.) it dries up, turning yellow and brittle, like horn. When in this condition, five times its weight of water will re-dissolve it bringing it once more to its original consistency. The only change which the albumen undergoes during the process of coagulation is the removal by the hot water of the alkali and soluble salts. Its chemical composition remains the same throughout.
Albumen may be prepared In a pure state from white of eggs, by the following method :—The white of eggs is beaten up well with water and filtered. To the filtrate is added a small quantity of sub-acetate of lead, in order to remove the mineral substances. The whole of the albumen is now precipitated as albuminate of lend. This is stirred up with water, and carbonio acid gas is passed through, by which the albuminate of lead is decomposed ; carbonate of lead is precipitated, and the albumen remains in solution. The carbonate of lead is now filtered off through paper which has been washed with dilute acid. Traces of ledd still remain, and to remove these the filtrate is treated with a few drops of aqueous sulphuretted hydrogen, and gently heated. The first
flocks of albumen which appear, retain the whole of the lead as sulphide. This is filtered off, and tho filtrate evaporated gently in a basin, the residue consisting of pure soluble albumen.
Albumen may be obtained from the serum of blood by precipitating with lead acetate, washing and decomposing the precipitate while suspended in water, with carbonic anhydride. A cloudy solution of albumen is obtained on filtration ; this is evaporated at a temperature of about 50°, and a yellow transparent substance is left, consisting of nearly pure albumen. It is partly soluble in water, but entirely so on addition of a little acetic acid. Alcohol precipitates it from its aqueous sol ution.
Albumen is insoluble in alcohol and ether. Strong alcohol, in large excess, precipitates it from its aqueous solutions; so also does ether,'but in smaller quantities. Nearly all acids, except acetic acid, in which it is soluble, coagulate albumen. The alkaline earths form with it insoluble com pounds which harden on drying: A useful cement, which when dry sets as hard as stone, may be made by mixing slaked lime with white of eggs.
Albumen forms precipitates with salts of lead, mercury, silver, tin, and bismuth. It is there fore an effective antidote in cases of poisoning by sugar of lead, corrosive sublimate, or nitrate of silver, as it forms with these insoluble compounds, and thereby prevents the poison from entering the system.
Albumen is used chiefly for clarifying vinous and syrupy liquids. It is mixed with the liquid, to bo clarified, and heat is applied. The albumen coagulates, and in doing so retains all the minute insoluble impurities which rendered the liquid turbid, and which may now be skimmed off with it from the surface, leaving the liquid clear and bright. This process is largely used by sugar refiners (see Sugar). It is also used by calico printers as a mordant for fixing colours (see Dyeing, and Calico Printing), and in photography (see Photography). • The following method has been recommended by M. Berg for the preservation of egg-albumen for photographic purposes. The whites, separated from the yokes, are evaporated to dryness in zinc or porcelain basins, at a temperatnre of 45°, the operation being conducted in vacua to quicken the evaporation. The solid albumen thus obtained is afterwards reduced to powder, which, if kept perfectly dry, may be preserved for a long time without alteration, and may be employed for all the purposes of the ordinary article, such as the clearing of wines, &O. It is probable that it would serve equally well for the manufacture of albumenized paper.