1396 FOODS AND FOOD ADULTERANTS 



DETERMINATION OF NITROGEN AND NITROGENOUS SUB- 

 STANCES. a 



TOTAL NITROGEN 



Total nitrogen is determined in about 2 grams of the meat by means 

 of the Kjeldahl or Gunning method. In this laboratory rather better 

 results are obtained with the later method than with the former. The 

 percentage of total nitrogen obtained is multiplied by 6.25 for the 

 percentage of protein. 



COAGULATED PROTEIDS. 



About 2 grams of meat are boiled with water for fifteen or twenty 

 minutes, filtered, thoroughly washed with boiling water, and the 

 exhausted residue subjected to the Kjeldahl or Gunning method for 

 the determination of nitrogen. The percentage of nitrogen so obtained 

 is multiplied by 6.25 for the percentage of meat fiber or coagulated 

 proteids. 



PROTEOSES, PEPTONES, AND GELATIN. 



The method employed for this determination is that of Allen and 

 Searle b as modified by Dr. Wiley. 



The filtrate from the insoluble portions of the meat is received in 

 Kjeldahl flasks and used for the separation of the soluble proteid nitro- 

 gen by bromin. The filtrate is first acidulated with two or three drops 

 of strong hydrochloric acid and then about 2 cc of liquid bromin are 

 added and the contents of the flask vigorously shaken. If the bromin 

 be all taken up more is added until finally a globule of cc of liquid 

 bromin is left undissolved and the supernatant liquid is thoroughly 

 saturated with bromin. The mixture is then allowed to stand over- 

 night, by which time the precipitate will have settled. The super- 

 natant liquor is passed through filter paper and the precipitate in the 

 flask washed by decantation with water, the globule of undissolved 

 bromin serving to saturate the wash water so that it is unnecessary to 

 use additional bromin water for the washing. The filter containing 

 the precipitate is returned to the same flask in which the precipitation 

 has taken place and the nitrogen therein determined by the Gunning 

 method. The sum of the nitrogen in the part insoluble in water arid 

 the part precipitated by bromin is subtracted from the total nitrogen 

 determined on the original sample, and the difference gives the total 

 nitrogen in the flesh bases. 



More recent results in this laboratory indicate that bromin does not 

 precipitate from aqueous solution all the proteoses and peptone pres- 

 ent. At the same time, considering the small amount of these bodies 



a The nitrogen of all samples described in this bulletin was determined by Mr. 

 T. C. Trescot. 



b The Analyst, 1897, 22, 258-263. 



U. S. Dept. of Agr., Div. of Chem. Bui. 54. 



