NITROGEN IN CHEESE. 233 



Fat. The dry residue from the water-determination is 

 extracted for twenty-four hours with water-free ether, which 

 has beentlried over sodium. 



Nitrogen I. Total Nitrogen. Ten grammes of the sand mix- 

 ture are analysed by Kjeldahl's method (p. 171). 



II. Applicability of Copper Hydrate to the Precipitation 

 of Albuminoids. Formerly, Stutzer employed copper hydrate 

 to separate proteins and their primary cleavage products from 

 secondary products (amino-compounds, etc.). He has since found 

 that it .only precipitates trypto-peptones (pancreas-peptone) 

 partially, and, extending his experiments to cheese, finds that 

 there is sometimes a peptone present which is not completely 

 precipitated. 



III. Phospho - tungstic Acid as a Precipitant. The con- 

 clusions of Bondzynski that phospho-tungstic acid is a suitable 

 separating agent are confirmed. By its means the proteins and 

 their primary cleavage products (albumoses and peptones) are 

 separated from the secondary products (phenyl-amino-propionic 

 acid, leucine, tyrosine, and other amino-compounds) and am- 

 moniacal compounds, all of which Stutzer classes as worthless. 

 The substances belonging to the first group may be divided 

 further into (a) Indigestible nitrogenous matters ; (6) Albu- 

 moses and peptones soluble in boiling water ; and (c) Proteins 

 insoluble in boiling water. 



IV. Nitrogen in the Form of Ammoniacal Salts. An 

 amount of the sand mixture corresponding to 5 grammes of 

 cheese is mixed with 200 c.c. of water and the ammonia dis- 

 tilled, after the addition of barium carbonate. Magnesia and 

 magnesium carbonate cause a partial decomposition of the 

 amides. The author prefers to operate on a portion of the 

 hot- water extract. 



V. Nitrogen in the Form of Amino Acids. This is taken 

 to be the nitrogen belonging to those compounds in the cheese 

 which are not precipitated by phospho-tungstic acid, and which 

 are not ammoniacal compounds. An amount of the sand 

 mixture, corresponding to 5 grammes of cheese, is mixed with 

 150 c.c. of water, and shaken well for fifteen minutes in a closed 

 vessel. After standing for fifteen hours at the ordinary tem- 

 perature, 100 c.c. of dilute sulphuric acid (1 vol. : 3 vols. water) 

 are added, and phospho-tungstic acid so long as a precipitate 

 results. The liquid is filtered, the precipitate washed with 

 dilute sulphuric acid until the filtrate amounts to 500 c.c., and 

 the nitrogen is determined in 200 c.c. of this. By deducting 

 from the amount that previously found as ammoniacal 

 nitrogen, the nitrogen present in the form of amino acids is 

 found. 



