194 ANIMAL AMIDES. 



ed, and, unless the temperature is kept down, sulphurous acid is 

 disengaged, and the fibrin becomes black. When the acid is di- 

 lute, or when water is poured on the jelly, the fibrin suddenly 

 contracts to less than its original bulk. This contracted mass is 

 a compound of sulphuric acid and fibrin. When it is collected 

 on a filter, and washed with water, it becomes transparent and 

 gelatinous, and at last dissolves completely in water. This so- 

 luble matter is a neutral compound of sulphuric acid and fibrin. 

 The addition of sulphuric acid renders it insoluble as at first. 



Nitric acid gives fibrin a yellow colour. When cold and di- 

 lute, it forms two compounds with fibrin, as sulphuric acid does, 

 and having the same characters. But when heat is applied, and 

 the acid is strong, azotic gas is given out, the acid becomes yel- 

 low, and the fibrin is converted into a yellow or orange mass, 

 which does not dissolve in water. This substance was first de- 

 scribed by Fourcroy under the name of yellow acid. 



Pyrophosphoric acid produces with fibrin the same phenomena 

 as sulphuric acid. With common phosphoric acid, fibrin does 

 not swell into a jelly, but forms a compound soluble in water, and 

 not precipitated by an excess of acid. 



In concentrated acetic acid fibrin becomes immediately soft 

 and transparent, and, with the assistance of heat, is converted 

 into a tremulous jelly. By adding hot water, this jelly is 

 completely dissolved with the evolution of a small quantity of 

 azotic gas. The solution is colourless, and has a mawkish and 

 slightly acid taste. During its evaporation a transparent mem- 

 brane appears on the surface, and after a certain degree of con- 

 centration the gelatinous substance is again reproduced. When 

 completely dried it is a transparent mass which reddens litmus- 

 paper, but is insoluble in water without a fresh addition of acetic 

 acid. When ferrocyanate of potash, an alkali, or sulphuric, ni- 

 tric, or muriatic acid is dropped into this solution a white preci- 

 pitate falls. The acid precipitate is a compound of fibrin and the 

 acid. If it be washed, a certain portion of acid holding fibrin 

 in solution is carried off, and the remainder is soluble in water. 

 This solution contains a neutral compound of the acid and fibrin. 

 The addition of a little more of the acid causes it to precipitate 

 again. * 



* Berzelius, Annals of Philosophy, ii. 20. 



