Tritoxide of Though protein may be said to be absolutely insoluble in water, it may by prolonged ebullition with ac cess of air be rendered completely soluble. This is owing to the formation of a soluble oxide of protein, represented by the formula C40 1-131 N5 0, 5 ± HO, containing three additional equivalents of oxygen, and which Mulder has called tritoxide of protein. This interesting compound may be more easily prepared from the chlorite of protein (which I shall presently describe) by the addition of ammonia ; the muriate of ammonia which is formed at the same time being afterwards separated by washing with alcohol.
Tritoxide of protein has, when dry, very much the same appearance as protein ; it is readily soluble in water, nearly insoluble in alcohol, and completely so in ether. It dis solves in sulphuric and hydrochloric acids and the alkalies, but is precipitated from its solution in water by dilute sulphuric acid, tannin, and several metallic salts, forming compounds with their oxides, having for the most part the formula (C. „ H3, N, 0,5 + MO) + (C4 „ H3, N5 0,, H 0). With nitric acid it behaves like protein, becoming yellow, and forming xanthoproteic acid. Water in which meat has been boiled, as broth, soup, &c., owes its nourishing properties mainly to the tritoxide of protein which is formed during ebullition ; and according to Mulder, both this and the binoxide are formed in meat during the process of roasting.
Binoxide of The other compound of protein and oxygen just alluded to, called by Mulder the binoxide, consists of C40 H3 , N, 0,4 or the elements of protein plus two equivalents of oxygen. Both this and the tri toxide exist ready formed in the huffy coat of the blood, which, according to Mulder, con sists chiefly of these two oxides. Binoxide of protein may be obtained by boiling fibrin in water for many hours, when the protein gra dually combines with at first two, and even tually three equivalents of oxygen, becoming successively binoxide, and (if the ebullition is continued long enough) tritoxide ; the latter dissolves as it is formed, and may be separated from the insoluble binoxide by washing with water. This process is, however, tedious, and it is more readily obtained from hair, in the following manner. The hair should be freed from grease by washing with ether, and dis solved in rather a dilute solution of caustic potash, with the aid of a gentle heat, not ex ceeding 120° or 130°. A mixed solution of
protein and its binoxide is in this way obtained, teom which the protein is first separated by neutralizing the solution with acetic acid, and after filtration the binoxide is precipitated by the further addition of a decided excess of acid. It appears as a yellowish flocculent precipitate, and when washed and dried has a dark resin like appearance.
Bouchardat obtained a substance by digest ing moist fibrin in water acidified with one or two-thousandth of its weight of hydrochloric acid, in which it gradually dissolved, which he called albunanose ; it has since been prepared and analysed by Blulder, who considers it to be identical with binoxide of protein ; but Liebig, who has recently examined it, says that it cannot be obtained free from sulphur, and consequently that it is not pure binoxide of protein. This oxide is insoluble in water, alcohol, and ether, but dissolves in most of the dilute acids, and in solutions of potash and ammonia ; it is precipitated from its acid solu tions by ferrocyanide and ferridcyanide of' po tassium, and several other metallic salts. Nitric acid decomposes it, forming xanthoproteic acid, but the yellow colour produced by it is less intense than that obtained with protein.
These oxides of protein possess considerable physiological interest, from the circumstance that they are contained in the blood, in small quantity during health, but much more abun dantly in some forms of disease. It is probable that they are formed during every act of respi ration by the action of the inspired oxygen on the globules or fibrinous matter of the blood ; and Mulder is of opinion that it is through their instrumentality that the atmospheric oxygen is conveyed to the capillaries, there to be employed in effecting the necessary changes in the substance of the body. During fever, when respiration goes on with more than ordinary rapidity, these oxides are formed in much larger quantity ; hence the buffy coat of diseased blood, which was formerly considered to be merely fibrin, consists almost entirely of oxidized protein ; and pus, false membranes, and other morbid products contain it in con biderable quantity.