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. Albumen also combines with lime and baryta; and chloride of barium has been recommended in positive printing upon albumenized paper, probably from this cause. _Chemical composition of albumen._--Albumen belongs to the _nitrogenous_ class of organic substances. It also contains small quantities of sulphur and phosphorus. Alcohol. Symbol, C{4}H{6}O{2}. Atomic weight, 46. Alcohol is obtained by the careful distillation of any spirituous or fermented liquor. If wine or beer be placed in a retort, and heat applied, the alcohol, being more volatile than water, rises first, and is condensed in an appropriate receiver; a portion of the vapor of water, however, passes over with the alcohol, and dilutes it to a certain extent, forming what is termed "spirits of wine." Much of this water may be removed by redistillation from carbonate of potash; but in order to render the alcohol thoroughly _anhydrous_, it is necessary to employ _quick lime_ which possesses a still greater attraction for water. An equal weight of this powdered lime is mixed with strong alcohol of ·823, and the two are distilled together. _Properties of Alcohol._--Pure anhydrous alcohol is a limpid liquid, of an agreeable odor and pungent taste; sp. gr. at 60°, ·794. It absorbs vapor of water, and becomes diluted by exposure to damp air; boils at 173° Fahr. It has never been frozen.