ii PRIMARY DISSOCIATION-PRODUCTS 23 



Therefore 21 per cent hydrochloric acid is used whenever the amount 

 of polarisation of different amino-acids has to be determined. 



Glycocoll, 1 as its name indicates, as well as other a-amino-acids, 

 possess a sweet taste, while /?- and y-amino-acids are tasteless. 2 The 

 two stereoisomers have the same taste. 2 



Methods of preparing and estimating Mono-amino- Acids 



To prepare and estimate mono-amino-acids the following plan used 

 to be adopted : The mixture of albuminous dissociation -products was 

 inspissated, after the removal of the hydrochloric and sulphuric acids 

 by means of cupro-oxide Cu 2 and barium hydrate, when leucin and 

 tyrosin crystallised out because of their slight solubility. Although 

 the solubility of these acids is greatly increased through the 

 admixture of other dissociation -products, yet tyrosin separates out 

 in large quantities. In their impure state both tyrosin and lysin 

 crystallise out in very characteristic forms, which on microscopical 

 examination cannot be mistaken, for tyrosin appears as needle-like 

 conglomerations, while leucin forms round somewhat dentate nodules. 

 The presence of these nodules has been considered for a long time 

 to be the most ready means of diagnosing the presence of primary 

 crystalline dissociation-products. 



To separate leucin from tyrosin, Habermann and Ehrenf eld 3 use 

 boiling glacial acetic acid, which readily dissolves leucin, while it has 

 hardly any effect on tyrosin. Tyrosin is obtained as a rule in fairly 

 pure crystals, while leucin is always contaminated by many impurities. 4 



Till quite recently no generally applicable method was known for 

 separating other amino-acids from one another. Glycocoll may separate 

 out if it be prepared from gelatine, as the latter is very rich in 

 glycocoll. Glutaminic acid, 5 or especially its hydrochloride, 6 if they be 

 present in large amount, also separate out, because glutamin-hydro- 

 chloride is nearly insoluble in strong hydrochloric acid. But, even 

 if the amino-acids which have been just enumerated could be obtained 

 as fairly pure crystals, there remain other amino-acids which will not 

 crystallise, 7 because all amino-acids, being both acid and basic in their 



1 H. Braconnot, Ann. de Chim. etde Physique, 13. 113 (1820). 



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



^ 3 J. Habermann and R. Ehrenfeld, Zeitschr. /. physiol. Chem. 37. 18 (1902). 

 * 4 E. Fischer, ibid. 33. 151 (1901) ; Ber. d. deutsch. chem. Ges. 34. I. 433 (1901). 



5 H. Ritthausen, Journ. f. prakt. Chem. 107. 218 (1869). 



6 H. Hlasiwetz and J. Habermann, Liebig's Ann. 169. 150 (1873) ; R. Cohn 

 Zeitschr. f. physiol. Chem. 26. 395 (1899). 



7 H. Ritthauseu, Journ. f. prakt. Chem. 1O3. 236 (1868) ; F. Kutscher, End- 

 produkte der Trypsinverdauung, Habilitationsschrift. Marburg, 1899. 



