Albumen thus prepared is brittle, semitrans parent, without taste or smell, and almost colourless. When burnt it leaves avery minute quantity of inorganic residue, which seems to be quite free from alkali : this fact is important, as it tends to settle a question which has been long disputed, viz. whether pure albumen is really soluble in water, or whether its solubility is due to the free alkali with which it is usually associated. If dry albumen be digested with water in a moderately warm place it readily dissolves, but a small insoluble residue always remains. According to Wurtz a solution of pure albumen begins to coagulate when heated to about 140° ; but if it be perfectly dry it may be raised to 280° or 290° without losing its solubility. It appears to have a slightly acid reaction, and if digested at a gentle heat, with a solution of carbonate of soda, it dis places the carbonic acid and combines with the soda. The albumen contained in white of eggs is composed of C, .0 Hs , Ns 0 0, 2,„ SP, or ten equivalents of protein plus one equiva lent of sulphur and phosphorus ; while that obtained from the serum contains an additional equivalent of sulphur, or C," 11810 N60 0, v, S. P. It is usually associated with from two to five per cent. of inorganic salts.
The appearances presented by albumen with reagents are in most cases very shnilar to those of protein, which I have already described, and its solution in hydrochloric acid has the characteristic blue colour. Most of the acids precipitate it from its solution, but this is not the case with tartaric, acetic, and tribasic phos phoric acids. Hence nitric acid is often used to detect albumen in the secretions. Another delicate test for albumen is ferroeyanide of potassium, which gives a white precipitate even with acid solutions ; the ferridcyanide of potas sium gives a yellowish precipitate. The appli cation of heat is also a good test for this principle: but as the presence of free alkali tends to prevent its c,oagulation, it is always ad visable to add at the same time a drop or two of nitric acid, when, if both cause a precipitate, the presence of albumen may be considered certain: it must be remembered too that the presence of those acids which do not precipi tate albumen, such as the tribasic phosphoric, tartaric, and acetic, also interferes with its coagulation by heat. Many of the metallic salts, when added to albumen, form insoluble precipitates, which are in roost cases conipounds of albumen with the acid or the base of the salt. A drop of a solution of bichloride of mercury will thus indicate the presence of albumen, even when diluted with two thousand times its weight of vvater; and this property of forming an insoluble compound has been taken advantage of in the treatment of cases of poi soning with the bichloride, when the white of egg has been found of great service ; the white of one egg being sufficient, according to the experiments of Peschier, to neutralize the effects of four grains of the poison. Albumen
is precipitated from its solutions by many other substances, as tannic acid, creosote, al cohol, and ether ; and its coagulation may also be effected by a current of voltaic elec tricity. When taken into the stomach it is coagulated by the free acid usually present.
The curious change which albumen under goes from the soluble to the insoluble condition is but very imperfectly understood, and it is not known how far the physical state of that coagulated by heat resembles that rendered insoluble by alcohol and the other precipitants. It is said that if an egg be smeared with oil immediately after it is laid, and afterwards ex posed to heat, the coagulation is incomplete. Coagulated white of egg readily dissolves in alkaline solutions, and is reprecipitated un changed if the solution be supersaturated with sulphuric acid. If it be digested at a tempe rature of about 120°, with a tolerably strong alkaline solution, the sulphur and phosphorus are separated from the protein; but if the alka line solution be boiled, further decomposition takes place ; ammonia is given off, and leucin, protid, and other compounds are formed. If the alkaline solution in which white of egg is boiled be rather weak, it acquires, after some hours' boiling, a smell precisely similar to that of boiled fowl. Though perfectly insoluble after coagulation, both in cold and boiling water, it appears to dissolve when heated under pressure to about 300° with that liquid, and the solution thus formed behaves in every re spect similar to uncoagulated albumen. When exposed to the air in a moist state albumen is extremely prone to enter into putrefaction; but if dry it may be preserved unchanged for any length of time. If boiled for several hours in water it is converted into tritoxide of pro tein, without passing through the intermediate stage of binoxide, in which respect it differs from fibrine.
The ready convertibility of albumen into the other protein compounds, as well as into many other animal tissues, is well illustrated in the phenomena of incubation ; where we find all the various compounds which are contained in the hatched bird, derived more or less directly from this substance, which, together with a yellow oil and some inorganic salts, constitutes the whole of the solid contents of the egg.