Amino Nitrogen and its Applications 47 



air. This is repeated to make absolutely certain that no air 

 remains ; then the outlet is closed until a gas space of from 1 5 to 

 18 c.c. has formed. The stopcock of the dropping funnel is then 

 closed and the outlet connected with a gas burette. The amino 

 solution is run in from the 10 c.c. burette, and the bottle shaken 

 at short intervals to hasten the evolution of gas. The latter is 

 continued until 30 to 40 c.c. more gas, than the volume of nitrogen 

 expected, is in the gas burette. The cock of the dropping funnel 

 is then opened, and all the gas from the bottle and outlet tube dis- 

 placed into the gas burette. This mixture of nitric oxide and 

 nitrogen is now run into a Hempel pipette containing a 5 per cent, 

 potassium permanganate 2.5 per cent, potassium hydroxide solu- 

 tion, which absorbs the nitrous oxide. The pure nitrogen is then 

 measured in the burette. 



Alanin, valin, leucin, glycocoll, aspartic acid, glutaminic acid, 

 phenylalanine, serine, oxyprolin, tyrosin, arginin, histidin, trypto- 

 phan, and guanin yield one molecule each of nitrogen. Lysin 

 yields 2 molecules of nitrogen. Prolin, being an imino substance, 

 does not react at all. Guanidine and its derivatives also fail entirely 

 to react. 



This method will be of value for convenient analysis in identi- 

 fying the amino acids, also for the estimation of the amount of 

 amino nitrogen in unknown substances, and in mixtures such as 

 hydrolyzed protein. It further renders possible an accurate deter- 

 mination of the prolin obtained by the ester method. The alco- 

 holic extract of the amino acids, whose esters distill below 100 0 , 

 contains prolin with a hitherto undeterminable amount of the other 

 acids as impurities. The amount of these impurities can be deter- 

 mined by amino nitrogen estimation, and this nitrogen subtracted 

 from the total, gives the prolin nitrogen. Histidin and arginin, as 

 obtained in solution by the Kossel and Patten method, can be 

 analyzed without isolation. The ratio, total N : amino N, in the 

 case of histidin is 1 : 3, of arginin 1 : 4, and as these ratios are 

 characteristic, amino and Kjeldahl determinations on their separate 

 solutions are sufficient to identify these bases. 



The amino nitrogen method has been made the basis of a 

 quantitative determination of amino nitrogen (amino acids) in the 

 urine. Urea and ammonia react slowly with nitrous acid so must 



