PROTEIN. 7 



ether, and is devoid of odour and taste. It readily absorbs 

 moistiu'e, and swells up, but regains its original form upon being 

 beated to 212°. 



Mulder lias analysed protein from animal and vegetable albu- 

 men, from fibrin, and from cheese or casein ; Scherer has analysed 

 it from animal albumen and fibrin, from the crystalline lens, 

 from hair, and from horn ; and Dumas from animal albumen 

 and casein. 



The formulae which these chemists have assigned to it approxi- 

 mate closely to each other, although they are not absolutely 

 identical. As Mulder's original formula has been confirmed by 

 the recent investigations of Schrdder and Von Laer,Ave shall adopt 

 it as the correct symbol of the composition of this substance. 

 According to this view the composition^ of an atom of protein is 

 represented by the formula C^^ H^j N^ O,,. Its atomic Aveight 

 is 5529*5, oxygen being 100, and its symbol is Pr. It burns 

 when exposed to the aii*, without leading any ash. When boiled 

 for a considerable time in water, with free exposure to the an-, 

 protein becomes slowly oxydised. We shall revert to this sub- 

 ject presently. 



Protein combines both with acids and bases. It dissolves 

 in all very dilute acids, and forms with them a kind of neutral 

 compound, which is insoluble or nearly so when there is an 

 excess of the acid present. Hence if sulphuric, hydrochloric, 

 or nitric acid be added to a solution of protein in a dilute acid, 

 the protein is precipitated in an insoluble state ; if however the 

 excess of acid is removed by careful washing, the precipitate 

 becomes again dissolved. Acetic acid and the ordinary (tribasic) 

 phosphoric acid constitute an exception to this rule as they dis- 

 solve protein in all proportions. Protein may be precipitated 

 from any of its acid solutions by ferrocyanide and ferridcyanide 

 of potassium, by tannin, by anhydrous alcohol, by various me- 

 tallic salts, and by the alkalies. 



Tlie Metamorphoses of Protein, a. Sulphuric acid and 

 proteiti. On the addition of concentrated sulphiu'ic acid to 

 protein or to any of its modifications (albumen, fibrin, or 



' Liebig's formula for protein is C^g Hgg Ng 0,^. The numerical results afforded 

 l)y these formula; approximate very closely. See Appendix I, Note 1. 



