ii PRIMARY DISSOCIATION-PRODUCTS 25 



which remains after the esters have been extracted with ether, oxy- 

 a-pyrrolidin-carboxylic acid l is obtained, while the residue which is left 

 after the distillation of the esters yields leucinimide. 2 Part of the 

 glutaminic acid was obtained also directly as the hydrochloride, 2 while 

 tyrosin was allowed to crystallise out according to the old plan. 3 

 The reconversion of the esters into the amino- acids is brought 

 about by boiling with water if the esters have a low boiling-point, 

 and by means of barium hydrate if the boiling-point is high. 

 This method of Fischer is the one on which, so far, the quantitative 

 determination of various amino -acids has been based. A second 

 method introduced by E. Fischer and Bergell 4 depends on the con- 

 version of amino -acids into /3-naphthalin-sulpho-derivatives, which, 

 because of their slight solubility, are especially suitable for the 

 separation of amino -acids. This second method has been used 

 successfully by Abderhalden, 5 Abderhalden and Bergell, 6 and Fischer 

 and Bergell. 7 Serin in particular was studied as serin-/3-naphthalin 

 sulphonate. 8 Amino-acids may also be coupled with phenyliso- 

 cyanate, and the resulting compounds be used for the identification 

 of the amino-acids. 9 



Siegfried 10 employs for the isolation of the complex dissociation- 

 products of albumins the substance 4-nitrotoluol-2-sulphoglucin 



C 6 H 3 N0 2 CH 3 S0 2 NH CH 2 COOH. 



An ethereal solution of this substance shaken with an alkaline solution 

 of amino-acids, e.g. glycocoll, alanin, glutaminic acid, yields after acidi- 

 fication with hydrochloric acid well-marked crystals, slightly soluble in 

 water and possessing a well-defined melting-point. For purification 

 the crystals are dissolved in hot water, and are then allowed to 

 crystallise out by cooling the water. 



Even E. Fischer's method gives, however, only minimal values, as 

 ' in the isolation of individual dissociation-products losses are unavoid- 

 able ; to obtain amino-acids quantitatively is impossible even after 

 a triple esterification, for the residue still possesses a very strong smell 



1 E. Fischer, Ber. d. deutsch. chem. Ges. 35. III. 2660 (1902). 

 V^ E. Abderhalden, Zeitschr. f. physiol. Chem. 37. 499 (1903). 

 V 3 E. Abderhalden, ibid. 37- 484 (1903). 



4 E. Fischer and P. Bergell, Ber. d. deutsch. chem. Ges. 35. III. 3779 (1902). 

 ~ 5 E. Abderhalden, Zeitschr. f. physiol. Chem. 38. 557 (1903). 



6 E. Abderhalden and P. Bergell, ibid. 39. 9 (1903). 



7 E. Fischer and P. Bergell, Ber. d. deutsch. chem. Ges. 36. II. 2592 (1902). 

 * 8 E. Abderhalden, Zeitschr. f. physiol. Chem. 37. 484 (1903). 



9 C. Paal, Ber. d. deutsch. chem. Ges. 27. II. 974 (1894) ; H. Steudel, Zeitschr. 

 ,f 'physiol. Chem. 34. 353 (1901) ; E. Fischer and A. Skita, ibid. 35.^221 (1902). 

 W 10 M. Siegfried, ibid. 43. 68 (1904). 



