14 BULLETIN 433, U. S. DEPAETMENT OF AGEICULTUEE. 



Proteose nitrogen wiis determined by the method of Baumann and Boiner 

 (1898). Five hundred cubic centimeters of extract was heated on a steam bath 

 to coagulate the protein, then neutralized to litmus paper by the addition of a 

 standard solution of sodium hydroxid, and finally concentrated to about two- 

 thirds of the original volume. The solution was then transferred to a 500 c. c. 

 flask, cooled, made to volume, and filtered ; and 400 c. c. of the filtrate Avas 

 concentrated on a steam bath to about 30 c. c. Particular care was taken that 

 the solution did not evaporate to dryness. To remove any coagulable protein 

 that might have separated out during the concentration, the solution was fil- 

 tered and the precipitate washed. The filtrate was then transferred to a 150 

 c. c. beaker and made up to 50 grams in weight. One cubic centimeter of 1-4 

 sulphuric acid and zinc sulphate in slight excess of the amount required to 

 saturate the solution were added. The solution was stirred at intervals to 

 insure complete saturation, and after 24 to 48 hours was filtered and the pre- 

 cipitate washed free of sodium chlorid by means of a saturated solution of 

 zinc sulphate acidified with 2 c. c. of 1—4 sulphuric acid to 100 c. c. of solution. 

 Nitrogen Avas determined in the precipitate. 



Amino nitrogen. — The term " amino nitrogen " is here applied to the nitrogen 

 liberated from the noncoagulable portion of the 0.9 per cent sodium chlorid ex- 

 tract by the action of an excess of nitrous acid. Part of this nitrogen may or 

 may not be derived from substances other than amino acids. Certain it is, how- 

 ever, that the greater the degree of proteolysis that a protein substance under- 

 goes, the more nearly will its split products resemble a mixture of amino acids, 

 and the greater will be its yield of free nitrogen when acted upon by nitrous 

 acid. The prime object of this determination, therefore, was merely to obtain 

 in a simple way comparative data as to the degree of proteolysis that had taken 

 place in the various samples as judged by the amounts of nitrogen yielded by 

 their reacting amino groups. 



For this purpose .500 c. c. of the extract was measured into a 600 c. c. beaker, 

 heated on a steam bath to coagulate the proteins, and after having been neu- 

 tralized to litmus paper, vvas evaporated to about 330 c. c. The solution and 

 coagulum were quantitatively transferred to a 500 c. c. volumetric flask, cooled, 

 diluted to the mark, and filtered. Four hundred cubic centimeters of this 

 filtrate was measured into a suitable beaker and evaporated to about 25 

 c. c. on a steam bath, after which the concentrated solution was quantitatively 

 transferred to a 100 c. c. beaker and further concentrated to a volume of about 

 10 c. c' The final concentrate was then quantitatively washed into a 25 c. c. 

 volumetric flask, cooled, diluted to the mark, and filtered to remove any addi- 

 tional coagulum that might have formed. A 10 c. c. aliquot of this filtrate was 

 used for the determination of amino nitrogen. 



The amino nitrogen was estimated by the method of Van Slyke (1912) in 

 the apparatus designed for that purpose. The 10 c. c. aliquot mentioned above 

 was introduced into the reaction compartment in the presence of an excess 

 of glacial acetic acid and potassium nitrite and the absence of air ; the nitrous 

 oxid and carbon dioxid formed were absorbed from the mixture of gases by 

 means of an alkaline solution of potassium permanganate in a gas pipette and 

 the residual nitrogen was measured in a nitrometer with the customary pre- 

 cautions. Although octyl alcohol was used to reduce foaming in the reaction 

 compartment, it was found impossible to shake the mixture continuously for 

 five minutes as prescribed by Van Slyke. The reaction period was therefore 

 lengthened from 5 to 20 minutes, and the uniform practice was adopted of 



1 An evaporating dish was found to be unsuitable for tbis purpose, since the solids left 

 upon its walls, as the level of the liquid recedes, are subjected to superheating that may 

 vitiate the results. 



