76 CHEMISTRY OF THE PROTEIDS CHAP. 



The Nitrogen Radicals of the Albumin-molecule 



To facilitate the difficult quantitative estimation of dissociation- 

 products, attempts have repeatedly been made to determine at least 

 some of the groups quantitatively. The most important method in 

 this respect is that which was worked out by E. Schulze, 1 Hausmann, 2 

 and others for the determination of the different forms in which 

 nitrogen is present. 



Hausmann's method of studying the distribution of nitrogen in the 

 proteid-molecule consists of the following operations : 



1. One gram of the substance under investigation is dissociated 



with boiling hydrochloric acid. 



2. The nitrogen which has been split off as ammonia, and which 



is present as ammonium chloride, is distilled off with magnesia. 

 This N. is the so-called ' amid-nitrogen,' ' ammonia-nitrogen,' or 

 ' readily displaceable nitrogen.' (It is absent in the protamins.) 



3. The fluid, freed from ammonia, is precipitated with phospho- 



tungstic acid, and the nitrogen present in the precipitate is 

 determined by Kjeldahl's method. This nitrogen is the ' di- 

 amino-nitrogen ' or ' basic nitrogen ' of arginin, lysin, and 

 histidin. 



4. The nitrogen which is not driven off by magnesia, and which 



is not precipitated by phosphotungstic acid, is then deter- 

 mined by Kjeldahl's method as the ' mono-amino-nitrogen.' 



Against this method Friedmann, 3 and particularly Kutscher, 4 have 

 raised the objection, that the phosphotungstates of the bases are not 

 insoluble, and that the bases are readily soluble in an excess of 

 phosphotungstic acid. As the latter is used for washing out the bases, 

 too low values are obtained for the bases, and these values differ also 

 according to the way in which the washing-out process is performed. 

 E. Fisher and Abderhalden 5 have recently overcome this difficulty 

 in not washing out the phosphotungstic acid precipitate at all, but by 

 pressing it out under a hydraulic press. But whether this method 

 is practicable has still to be determined. Kutscher 6 has investigated 

 casein by Hausmann's method, and has arrived at the conclusion that 



1 E. Schulze and E. Winterstein, Zeitschr. f. physiol. Chem. 33. 574 (1901), 35. 

 210 (1902). 



2 W. Hausmami, ibid. 27- 95 (1899), 29. 136 (1900). 



3 E. Friedmaun, ibid. 29. 50 (1890). 4 F. Kutscher, ibid. 31. 215 (1900). 



5 E. Fischer and E. Abderhalden, ibid. 39. 81 (1903). 



6 Compare with Hausmann and Kutscher, I.e. F. Miiller and J. Seemann, Deutsch. 

 med. Wochensch. 1899, p. 209. 



