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When protein, or any compound which furnishes it, is boiled in water for several consecutive hours, the protein gradually combines with oxygen, and becomes converted into a soluble substance, termed by Mulder trioxide of protein and ammonium (H ̧NO, 2 C36H25N4O13, 3 HO?): this compound is insoluble in alcohol and in ether. Its aqueous solution is precipitated by the mineral acids, by solutions of chlorine, of tannic acid, and by the salts of lead, of silver, of zinc, and of iron; but not by ferrocyanide of potassium, or by salts of barium. It forms neutral compounds with the alkalies; but if boiled with an excess of potash or of soda it emits ammonia. It is very probable that much of the material which figures in the analyses of animal products as 'watery extractive animal matter' consists of this body; and if so, it forms an important substance in connexion with the metamorphosis of albumin and of fibrin into the products which are carried off by excretion from the system.

When a current of chlorine is transmitted through a dilute solution of albumin, a compound is separated in white flocculi, which Mulder regards as a definite compound of chlorous acid with protein. This substance, when decomposed by ammonia, yields the ammoniacal trioxide of protein just described. This ammoniacal trioxide appears to exist in the buffy coat of the blood, which is formed upon the surface of the coagulum in blood drawn from patients suffering from certain acute inflammatory affections. In such cases, it is associated with an insoluble compound, described by Mulder as the dioxide of protein. The same chemist also regards this insoluble body as forming the principal constituent of the hair: it is of a yellowish colour, is soluble in alkalies, and is sparingly so in acetic acid. Mulder states that it is this compound which constitutes the insoluble residue obtained from fibrin after it has been boiled for many hours in water. It is probably similar to that found in horn; but the nature of this substance, and its relations to albumin, require further examination. Indeed, the existence of the whole of these protein compounds, as distinct principles, must be admitted to be very problematical.

(1650) ALBUMIN.-The properties of this body when in solution are subject to considerable modification, according to the nature of the substances with which it is associated. The reactions of albumin from the white of the hen's egg (ovalbumin), therefore, differ in some respects from those afforded by albumin contained in the serum of blood (seralbumin), and this again from soluble albumin freed as far as possible from saline mixture; and

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all of these forms of albumin differ slightly from the albumin contained in the urine as secreted in Bright's disease.

Soluble albumin, in an aqueous solution, is a tasteless, somewhat glairy, colourless liquid, which exerts a left-handed rotatory action upon a ray of polarized light. A solution of albumin is readily coagulated by heat, and by the addition of various saline and acid liquids. It may be evaporated to dryness at a temperature not exceeding 122° (50° C.), and may be preserved in the form of a yellowish, brittle, transparent mass, which is insoluble in alcohol and in ether; but it may be slowly redissolved in lukewarm water; the solution being greatly promoted by the addition of a small quantity of chloride of sodium or of any other salt of the alkalies. A considerable portion of the albumin is, however, always left in the insoluble form. If white of egg, or serum, be evaporated to dryness in vacuo, then powdered and digested in a small quantity of cold water, the greater portion of the soluble salts is dissolved, and at the same time a considerable quantity of albumin is found in the liquid; the residue, after being thus freed from its soluble salts, is almost insoluble. Albumin, in its purest form, has a slightly acid reaction upon litmus.

The most remarkable peculiarity of albumin is its power of solidifying on the application of heat, and of becoming insoluble. This coagulation begins at 140°; the solution, if concentrated, sets into a gelatinous mass, as is seen in the common process of boiling an egg hard; but when the liquid is very dilute, it simply becomes turbid. The albumin may, however, be separated by ebullition, provided that the solution be neutral or slightly acid; it then collects into flakes, which can be separated by filtration. Nothing is known of the cause of the coagulation of albumin by heat. When a solution of albumin containing alkali, such as serum or white of egg, is heated, a small quantity of sulphur is separated, and the liquid becomes rather more alkaline from the liberation of a portion of the soda from the coagulated mass. Seralbumin does not form so solid a coagulum as ovalbumin.

Coagulated albumin, when dried, forms hard, horny, transparent masses, of a yellowish colour. When plunged into cold water it absorbs four or five times its bulk of this liquid, and becomes opaque and elastic. It is not soluble in water, but by long boiling in open vessels it undergoes gradual decomposition, and a soluble compound is obtained, which has the composition of trioxide of protein and ammonium (1649). If heated to 300° with a small quantity of water, in a sealed tube, the albumin is redissolved, and furnishes a liquid which does not coagulate by heat,

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but which when acidulated with acetic acid gives a precipitate with potassic ferrocyanide.

Strong alcohol precipitates albumin from its aqueous solution; but if the alcohol be rendered slightly alkaline by the addition of potash, no coagulation ensues. Ether, if free from alcohol, does not occasion the coagulation of seralbumin, although it renders the concentrated solution of ovalbumin viscid, and gradually effects its complete coagulation. Kreasote occasions its immediate coagulation. The concentrated mineral acids precipitate albumin in a coagulated form, but gradually decompose it and dissolve it, acting upon it as they do upon the compounds of protein generally: oil of vitriol dissolves it with a brownish-red colour, nitric acid produces with it a lemon-yellow, and warm hydrochloric acid a violet-coloured solution after some hours' digestion. Nitric acid precipitates it, and when dilute does not redissolve the precipitate. Hydrochloric acid precipitates it and redissolves the coagulum; the solution when poured into a small quantity of water becomes milky, but is rendered clear by the further addition of water. The solution of coagulated albumin in strong hydrochloric acid furnishes syntonin, the same substance which is produced by the action of the dilute acid on muscular fibre (1655). Dilute sulphuric acid produces no precipitate till the liquid is boiled; the clear solution in concentrated sulphuric acid is not precipitated when diluted with water. Metaphosphoric acid causes an immediate coagulation of albumin; but the other varieties of phosphoric acid produce no such effect. Acetic acid, and the organic acids generally, except the modification of tannic acid which is contained in infusion of galls, do not produce any precipitate in solutions of albumin.

The solutions of albumin in the organic acids are not coagulated by boiling, but a pellicle is gradually formed over the surface during evaporation; the addition of a solution of some salt, such as sodic sulphate or chloride, causes the albumin to separate from these solutions. The precipitates from the unboiled solutions are generally soluble in pure water; precipitated albumin is, therefore, not necessarily in the coagulated form. If a solution of white of egg be ren. dered accurately neutral by the addition of acetic acid, and then be diluted, flocculi of albumin are precipitated, but they are redissolved when treated with a solution of common salt or of nitre.

Solutions of alum, and of many of the metallic salts, such as those of copper, lead, mercury, or silver, precipitate solutions of albumin. It is, therefore, useful to administer whites of eggs in the liquid form in cases where poisoning from swallowing any of

EFFECT OF BASES ON ALBUMIN.

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the salts of these metals is suspected to have occurred; the remedy is a safe one, whilst if the poison have really been taken, the albumin decomposes the salt, and generally enters into combination both with the acid and the base; the albumin sheathing the stomach from the influence of the poison, whilst other measures are in preparation for effecting its removal from the system.

(1651) Effect of Bases on Albumin.-The presence of an alkali in liquids containing albumin considerably modifies the reactions; if the alkali be present in large quantity, the solution does not coagulate when heated, but a pellicle is formed over the surface during the evaporation, an appearance being thus produced similar to that observed when milk and other solutions of casein are exposed to the air whilst hot.

Albumin forms definite compounds with the alkalies and other metallic oxides. Coagulated albumin is dissolved freely by solutions of the alkalies, and in certain proportions it even neutralizes their action upon test-paper. If a concentrated solution of albumin be mixed with one of potash, a gelatinous mass of potassic albuminate is formed, from which, by washing with cold water, the excess of alkali may be removed; it retains 5'4 per cent. of potash (Lieberkuhn). If the gelatinous mass be washed with alcohol and then with water, it is insoluble in boiling water and also in boiling alcohol; but if it be washed with cold water only, the residue is soluble both in boiling water and in boiling alcohol. The aqueous solution of potassic albuminate is not coagulated by boiling it, but on the addition of a small quantity of acetic, tartaric, or phosphoric acid, a white coagulum is produced, which is readily dissolved by an excess of the acid. These characters resemble those of casein, and some chemists have supposed that casein is simply an albuminate of potassium. The coagulum obtained by the addition of acetic acid to the solution of potassic albuminate, when well washed, furnishes nearly pure albumin. It leaves scarcely any ash on incineration.

Sodic albuminate resembles the potassic compound, and may be formed in a similar manner. The animal fluids in which albumin occurs, such as the white of the egg and the serum of the blood, are very slightly alkaline, the proportion of alkali not exceeding 158 per cent. in ovalbumin (Lehmann). Even this small proportion renders the albumin more soluble, and prevents its complete coagulation on boiling, a portion of albumin remaining dissolved and forming sodic albuminate: and that portion of the albumin which does coagulate does not collect into flocculi. Sodic albuminate may be readily decomposed by neutralizing it

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ALBUMIN PREPARATION.

with acetic acid; on afterwards boiling it, the albumin is separated in coherent flocks. It is also to be remarked that the albumin may be made to separate from the slightly alkaline liquid by boiling it after the addition of a neutral salt, such as sodic sulphate, common salt, or hydrochlorate of ammonia. These are points which require attention in the analysis of animal liquids, in which the quantitative separation of albumin is necessary. Gerhardt is disposed to view serum and the white of eggs as containing a definite hydrosodic albuminate; and adopting Lieberkuhn's formula for albumin, it would be (HNa€,H110N18SO22 H2O). Such formula, however, can only be regarded as approximations.

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According to Lieberkuhn, the compound of albumin with silver is (AgHЄ,,H110N18SO2, H2O); that of copper (Eu¤,,H110N18SO, H2O); the copper compound is soluble in an excess of solution of cupric sulphate, as well as in an excess of a solution of potash ; in the latter case a deep blue liquid is formed resembling that obtained by adding ammonia in excess to the salts of copper. The presence of albumin in a solution consequently prevents the precipitation of the cupric salts by the alkalies, and a similar observation has been made in the case of the ferric salts. The compound of albumin with lead is obtained by adding basic acetate of lead to a solution of albumin; it is readily decomposed by all the acids. The albuminate of mercury is formed when a solution of white of egg is mixed with one of corrosive sublimate: it is very insoluble in pure water, but it is dissolved by a solution of

common salt.

Preparation. The preparation of pure albumin in the coagu lated form may be effected by precipitating white of egg by means of hydrochloric acid, washing with the same acid in a diluted form, and then dissolving in water: this solution is precipitated by carbonate of ammonium; the coagulum is washed, dried, and subsequently powdered, after which it is digested in alcohol and in ether, in order to remove traces of adhering fatty matters. Pure coagulated albumin may also be obtained by decomposing potassic albuminate by means of acetic acid.

Wurtz considers that a pure soluble albumin may be obtained in the following manner: white of egg is well agitated with twice its volume of water, and strained through linen in order to remove the membranous flocculi: the filtered portion is then mixed with a solution of basic acetate of lead, in quantity insufficient to throw down the whole of the albumin. The copious precipitate thus obtained must be well washed, suspended in water, and decomposed by means of a current of gaseous carbonic anhydride, when

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