118 § 85. BASES AND ACIDS WITH EEAGENTS. 



ized by acetic acid before this reaction can be obtained ; 

 if the solution is very dilute, the presence of albumen 

 will be shown by a flocculent precipitate, or a mere tur- 

 bidity, on being boiled. A solution of albumen is coagu- 

 lated also by plumbic acetate or cupric sulphate, but not 

 by acetic acid. 



Casein is not precipitated from its solutions by heat, 

 except that a film is formed on the surface of the boiling 

 liquid ; it is precipitated by acetic and other acids, and 

 the precipitate is soluble in an excess of acetic acid. 



Flhrine is precipitated from its solutions spontane- 

 ously, when they are removed from the influence of vital 

 forces. 



Quantitative estimation. — As it is almost impossible to 

 separate all of an albuminoid from its solution or from 

 matters mixed with it, pure and unaltered, or in the form 

 of any insoluble precipitate of a definite composition, the 

 amount of albuminous matters in a substance is usually 

 estimated froiji the amount of nitrogen in it. 



Albuminoids contain, on an average, 16° |^ of nitrogen; 

 therefore, the total weight of the albuminoid is VV = 6.25 

 times that of its nitrogen. Assuming, then, what is gen- 

 erally true, that all the nitrogen present in the dried 

 plant is part of an albuminoid, we multiply the weight 

 of nitrogen found in the substance by 6.25 for the weight 

 of the albuminoids. 



Determination of Nitrogen. — The method most gener- 

 ally applied in this case, as well as in agricultural analyses 

 generally, is that of Yarentrapp and Will, as modified by 

 Peligot, in which the nitrogen is converted into ammonia 

 by ignition with soda-lime, and the ammonia is absorbed 

 by a measured quantity of a standard acid ; the ignition 

 is performed in a thick-walled tube of hard Bohemian 

 glass, about 40 cm. long, and 12 mm. in diameter, drawn 

 out into a slender beak at one end that is bent upwards. 



