Acetate of Silver. (See [Silver, Acetate of.])
Albumen.
Albumen is an organic principle, found both in the animal and vegetable kingdom. Its properties are best studied in the white of egg, which is a very pure form of albumen.
Albumen is capable of existing in two states; in one of which it is soluble, in the other insoluble in water. The aqueous solution of the soluble variety gives a slightly alkaline reaction to test-paper; it is somewhat thick and glutinous, but becomes more fluid on the addition of a small quantity of an alkali, such as potash or ammonia.
Soluble albumen may be converted into the insoluble form in the following ways:—
1. By the application of heat.—A moderately strong solution of albumen becomes opalescent and coagulates on being heated to about 150°, but a temperature of 212° is required if the liquid is very dilute. A layer of dried albumen cannot easily be coagulated by the mere application of heat.
2. By addition of strong acids.—Nitric acid coagulates albumen perfectly without the aid of heat. Acetic acid, however, acts differently, appearing to enter into combination with the albumen, and forming a compound soluble in warm water acidified by acetic acid.
3. By the action of metallic salts.—Many of the salts of the metals coagulate albumen very completely. Nitrate of silver does so; also the bichloride of mercury. Ammoniacal oxide of silver, however, does not coagulate albumen.
The white precipitate formed on mixing albumen with nitrate of silver is a chemical compound of the animal matter with protoxide of silver. This substance, which has been termed albuminate of silver, is soluble in ammonia and hyposulphite of soda; but after exposure to light, or heating in a current of hydrogen gas, it assumes a brick-red color, being probably reduced to the condition of a salt of the suboxide of silver. It is then almost insoluble in ammonia, but enough dissolves to tinge the liquid wine-red. The author is of opinion that the red coloration of solution of nitrate of silver employed in sensitizing the albumenized photographic paper is produced by the same compound, although often referred to the presence of sulphuret of silver.