82 CHEMISTRY OF THE PROTEIDS CHAP. 



values in nitrogen-determinations are obtained by Kjeldahl's than by 

 Gunning- Arnold's method when working with albuminous substances, 

 that these contain either ring-like nitrogenous compounds which are 

 not decomposed, such as pyridin or piperidin-compounds, or substances 

 which by undergoing ring-formation give rise to pyridin or piperidin- 

 complexes. 



Effront 1 has pointed out that 'amides, imides, nitril bases, acid- 

 amides, and amino-acids react at ordinary temperature on alkaline hypo- 

 chlorite, and that thereby a loss of chlorine occurs which is propor- 

 tional to the weight of the added substance.' ' Ammonium bases do 

 not react with the hypochlorite solution.' The chlorine is estimated 

 with an arsenious acid, As 2 3 , solution. The total figures obtained for 

 egg -albumin, casein, Witte's peptone, etc., differ considerably from 

 those given above. 



Halogen-substituted Albumins 



Oswald 2 has drawn attention to still another characteristic of 

 albumins. It is possible to substitute halogens for the hydrogen-atoms 

 of such aromatic nuclei as phenylalanin, tyrosin, and perhaps trypto- 

 phane (see Chapter VII.), and therefore the amount of halogen which is 

 taken up by an albumin is a measure of the amount of aromatic nuclei 

 present in that albumin. Casein contains 7 per cent tyrosin and 

 phenylalanin, and at least T5 per cent tryptophane, while gelatine 

 contains no tyrosin or tryptophane, and only 0'4 per cent phenylalanin. 

 Correspondingly we find the casein-iodine compound to contain 11*43 

 to 13*45 per cent of iodine, while the gelatine-iodine compound con- 

 tains only T34 to 2'0 per cent iodine. As long, however, as we do 

 not know how many atoms of iodine are actually taken up by each 

 of the aromatic nuclei, we can, of course, only make approximate 

 estimations. See further p. 230. 



B. OTHER DISSOCIATION-PRODUCTS NOT YET CLASSIFIED 



Up till now only those dissociation-products have been enumerated 

 of which we know definitely that they are primary ones, and the 

 constitution of which is also sufficiently known. In the following 

 pages are enumerated some substances which have not been definitely 

 identified, or of which it is doubtful whether they are formed directly 

 from albumin or only secondarily out of those primary substances 

 described above. 



1 J. Effront, Ber. d. deutsch. chem. Ges. 37- 4290 (1904). 

 2 A. Oswald, Hofmeister's Beitrage, III. 514 (1903). 





