26 CHEMISTRY OF THE PROTEIDS CHAP. 



of esters, after the last ether-extraction. An accurate investigation 

 of the individual fractions shows that special attention has to be 

 paid to the higher fractions.' l The formation of leucinimide proves 

 further that secondary reactions are also taking place. E. Fischer and 

 Abderhalden 2 estimate the loss of amino-acids as amounting to 33 

 per cent when the ester-method is used, but the loss varies greatly 

 with each individual amino-acid. 



Methods for Preparing and Estimating Diamino Acids 



A more detailed account than that given here will be found in the 

 paper by Schulze and Winterstein. 3 



The methods for estimating the hexone-bases : lysin, arginin, and 

 histidin, have been worked out by Kossel and Kutscher. 4 After the 

 removal of the ammonia by distillation with barium carbonate, 5 the 

 mixture of dissociation - products is treated with an excess 6 of 

 silver sulphate, and then saturated with barium hydrate. Histidin 

 and arginin are hereby precipitated. They are now dissolved, the 

 barium and the silver are removed, the solution is treated with silver 

 nitrate, and barium hydrate is then added very carefully till the 

 histidin is precipitated. The latter is now purified by precipitation 

 with mercuric sulphate dissolved in sulphuric acid according to Kossel 

 and Patten. 7 The filtrate after the precipitation of the histidin is 

 saturated with barium hydrate, when arginin separates out, which 

 then may be converted into the sulphate or nitrate. From the filtrate 

 after the first silver precipitate, lysin is precipitated with phospho- 

 tungstic acid, and then converted into the picrate. This method has 

 the great merit of working quantitatively, if care be taken. 



The three hexone bases are therefore, along with ammonia, the 

 only dissociation-products of albumins, the amounts of which we can 

 express in definite percentage figures, instead of having to give 

 minimal values, as in the case of the mono-amino acids. For this 

 reason the hexone bases have received a great deal of attention during 

 the last few years, and we are more accurately informed regarding 

 their distribution than we are as to that of leucin and tyrosin, although 



J 



l E. Abderhalden, Zeitschr.f. physiol Chem. 37. 493 (1903). 

 * 2 E. Fischer and E. Abderhalden, ibid. 36. 268 (1902). 



3 E. Schulze and E. Winterstein, Ergebnisse d. Physiol. 1. 1, pp. 37-42 '(1902). 

 V* A. Kossel and F. Kutscher, Zeitschr. f. physiol. Chem. 31. 165 (1900). 

 * 5 E. Hart, ibid. 33. 347 (1901). j 



6 A. Kossel and F. Kutscher, ibid. 31. 165 (1900); F. Kutscher, ibid. 38, 111 

 (1903). 

 v 7 A. Kossel and A. J. Patten, ibid. 38. 39 (1903). 



