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Albumen or

silver, blood, acid, soluble, egg, liquid, lead, water, serum and white

ALBUMEN or ALBUMIN.—Albumen is the chief and characteristic constituent of the white of egg (albumen ori) and of the serum of blood. Albumen is also present in many other animal and vegetable substances. Commercial albumen is prepared either from the white of egg or from blood serum, the colorless liquid in which the corpuscles are suspended. White of egg consists of transparent, thin walled cellules enclosing an alkaline solution of albuminate of sodium. On beating it up with water, the cellular substance separates in pellicles, while the albuminate of sodium remains in solution together with chloride of sodium and phosphate of calcium. In srder to remove these mineral substances, the liquid, after being filtered from the cellular substaTce, is mixed with a small quantity of sub-acetate, of lead which produces an abundant percipitate (an excess of lead salt would redissolve it). This mass, after being washed, is stirred up with water to the consistence of a paste, and carbonic acid gas is passed through the liquid. The albuminate of lead is thereby decomposed, carbonate of lead remains suspended in the liquid, and the albumen in the free state remains dissolved. The solution is filtered through paper previously washed with dilute acid, and as it still retains traces of lead it is treated with a few drops of aqueous hydrosulphuric acid and carefully heated to 140 degs. until it begins to show turbidity ; the flocks of albumen thus precipitated carry down the whole of the sulphide of lead. When the liquid, which, after filtration, is perfectly colorless, is evaporated in large capsules at 140 degs. Fahr., a residue is obtained consisting of pure soluble albumen. If the same method be applied to the albumen of blood serum, it does not yield a perfectly pure product. Egg albumen differs from blood albumen by giving a percipitate when agitated by ether, scarcely soluble in strong nitric acid. If dried in the air, it forms a bright yellow, gumlike substance, easily triturated and reduced to a white powder which will not putrefy. It swells up in water like gelatine, but dis solves with great difficulty unless the addition of an alkali be made.

Blood albumen is usually prepared by collecting the blood in a flat-bottomed vessel, where it is allowed to stand for six or eight hours. The serum is then decanted into a filter and received in a vessel having a hole in the bottom of it fitted with a cork, through which a glass tube passes up above the level of the liquid. When the upper portion of the serum becomes quite clear the tube is lowered and the clear serum thus drawn off. It is then evaporated with a gentle heat and is ready for use. The blood of 5 oxen or 20 sheep yields about 2 lbs. of dry albumen.

Albumen is capable of existing in two very distinct modifications, viz., the soluble form, in which it always occurs in the human body, and the insoluble (in water) form. It is impossible to detect any difference between these two varieties, but when coagulation is determined by certain substances, the product is a compound of albumen with the agent used. Soluble albumen may be coagulated or converted into the insoluble form by heating to boiling point or by the action of alcohol or nitric acid. It becomes insoluble in water and alcohol, barely soluble in dilute potash,

but soluble in acetic acid. Many of the metallic salts serve to coagulate albumen ; nitrate of silver or bichloride of mercury, for instance. The chemical composition of egg and blood albumen is thus given : • Egg Albumen (Wilder). Blood Albumen.

Carbon 53.4 Carbon 53.4 Hydrogen 7.o Hydrogen Nitrogen is.o Nitrogen is 6 Oxygen 24.6 Oxygen 22.1 Sulphur — Sulphur 1.8 ioo.o 100.0 If nitrate of silver is added to a solution of albumen, a white precipitate is formed, caused by the combination of the animal matter with the protoxide of silver, termed albumenate of silver (see Silver Albumenate). If heated in a current of hydrogen gas, it assumes a reddish brown color. Albumen also combines with many other substances. It is preserved by the addi tion of ammonia or a piece of camphor floated on its surface. Commercial albumen is often adulterated with gum or starch ; to detect this adulteration, dissolve the albumen in warm water and add a little acetic acid ; if a precipitate be formed, gum is present. Starch may be detected by adding iodine to the solution ; it gives a black color.

Albumen is very extensively used for photographic purposes. It serves as a capital sub stratum to hold the silver salts, and combines with the silver to form silver albumenate. If the silver nitrate bath be too weak, the albumen will become soluble. Egg albumen is the best, though a large quantity of the albumenized paper now sold is prepared with blood albumen ; it has a disagreeable smell, however. Formerly it was largely used for glass negatives or posi tives, but is now used almost solely for paper positive processes, although it is sometimes used in collodion emulsions, owing to its property of giving greater sensitiveness to the film. In photo mechanical processes it is used on account of its possessing the same property as gelatine, of becoming insoluble on exposure to light when potassium dichromate is added to it.

Albumen is also employed in collodion emulsions owing to the greater sensitiveness it gives to the film, it being a much better halogen absorbent than pyroxlin. Owing to this fact glass, to be coated with a gelatine emulsion containing free nitrate of silver, is previously coated with albumen ; it causes the gelatine film to adhere firmly to the glass and prevents the crystal lization of the silver nitrate.

It is further of great service for clarifying purposes, because, if boiled with liquids, it coag ulates and clutches hold of all impurities and coloring matter, and carries them to the bottom or to the top, according, of course, to the density of the liquid. It is used in France under the tech nical name of glaise, to impart a gloss to card, paper and other surfaces. Its property of forming a hard compound, when mixed with lime, makes it very useful for compounding cement for laboratory purposes and for mending broken dishes, measures, etc.