PROTEIN, a substance obtained by Mulder from albumen, casein, horn, and animal and vegetable fibrin. When any one of these is dis solved in a solution of potash, and the filtered solution is mixed with a slight excess of acid, a copious grayish-white, flocculent precipitate is formed, and a slight smell of hydroaulphurio acid is perceived. This white substance is protein, so called from its occupying the first or most important place In relation to the albuminous principles.
Its properties are :—While moist the white flocculi are diaphanous, but by drying they become yellowish, hard and brittle. It possesses neither smell nor taste, attracts moisture rapidly from the air, and loses water at 2I2'. It is insoluble in water, alcohol, ether and essen tial oils. By long continued boiling in water it undergoes some change of properties, and is rendered soluble.
Acetio and phosphoric acids, whatever may be their state of con centration, dissolve it ; hydrochloric acid also dissolves protein, and acquires an indigo tint. When heated the solution blackens. With concentrated sulphuric acid It produces a jelly which contracts in water, and which, after being washed with water and alcohol, though it does not redden litmus-paper, contains 8.34 per cent. of sulphuric acid. Mulder calls this compound Sulphoprotcie acid. When protein is boiled in dilute sulphuric acid, it acquires a purple tint.
Protein is precipitated from its acid solutions by the ferro and ferrid cyanide of potasaium by tannin, and by neutralisation with an alkali. When strongly heated, protein is decomposed with the production of ammonia and a charcoal which burns with difficulty, but leaves no residue.
Protein consists entirely of carbon, hydrogen, nitrogen, and oxygen ; and it will he observed, that whether obtained from albumen (1), casein (2), horn (3), animal fibrin (4), or vegetable fibrin (5), the statements of its composition differ so slightly, as to show that it must be the same from whichsoever of the sources named it is procured.
to. /A1 In These analyses may be represented by the formula and consequently protein may be regarded as albumen in which two equivalents of sulphur are replaced by oxygen.
When protein, or the substances which yield it, are boiled in a con centrated solution of potash as long as ammonia is evolved, and the solution is afterwards neutralised by sulphuric acid, evaporated to dry ness, and the residue treated with boiling alcohol, three products of the decomposition are dissolved, one of which, erythroprotide, separates in oily drops as the solution cools ; lcucin is deposited in small crystal line scales by spontaneous evaporation ; whilst the mother water contains protide and formiate of ammonia in solution.
Binoxide, or oxyprotein, and tritoxide of protein are produced by the long continued action of boiling water upon fibrin in contact with air. They are the chief ingredients of the huffy coat of the blood in a state of inflammation, being produced at the expense of the fibrin.