ii SECONDARY DISSOCIATION-PRODUCTS 95 



nitric acid and thereby obtained very large quantities up to 30 per 

 cent of oxalic acid, which is not obtainable by the ordinary methods 

 (see below, under /). Habermann and Ehrenfeld found in addition 

 oxyglutaric acid, evidently derived from glutaminic acid and leucic 

 acid, while v. Fiirth obtained xanthomelanin. This is a friable, 

 blackish-brown powder having a bitter taste ; it is very slightly 

 soluble in water, ether, or chloroform, but readily soluble in ethyl-, 

 methyl-, amyl-alcohol, and in acetone ; it is most soluble in glacial 

 acetic acid, and is precipitated from such a solution by the addition 

 of water. In soda solution and in ammonia xanthomelanin dissolves 

 with a reddish-brown colour, and is evidently that complex which 

 gives rise to the xantho-proteic reaction (see p. 6). Xanthomelanin 

 prepared from casein has, according to v. Fiirth, the following 

 percentage composition : 



C H N S N0 2 



50-03 4-93 10-7 0-59 16'86. 



Fiirth could arrive at no definite conclusion as to the sulphur 

 radical. A preparation obtained from horn filings had a somewhat 

 different composition. 



On reducing the nitro-group with stannous chloride an acid was 

 obtained ; on being melted with a fixed alkali a distinct smell of 

 indol or skatol could be detected, which seems to indicate a certain 

 resemblance to tryptophane. This may also explain the remarkable 

 fact that on disintegrating casein with nitric acid no tyrosin is found 

 amongst the disintegration-products. 



(/) Disintegration by means of Nitrous Acid 



The reaction which is supposed to take place when albuminous 

 substances are brought into contact with either nitrous acid or an 

 alkali-nitrite + acetic acid may be represented, according to Levites, 1 

 thus : 



K - NH 2 + NO . OH = 2N + H 2 + K - OH. 



Schiffis of the opinion, as is Nasse and Hausmann 2 and Hofmeister, 3 

 that in the albumin -molecule are contained at least two CONH 9 - 

 groups, as is explained on p. 141, where the biuret-reaction is dis- 

 cussed. Schiff has stated that desamination leads to a disappearance 

 of the CONH 2 -groups, and that this disappearance also explains the 

 absence of the biuret-reaction with desamino-peptones. 



1 S. Levites, Zeitschr. f. physiol. Chem. 43. 202 (1904). 

 ' 2 Hausmann, ibid. 27. 95 (1899), and 29. 136 (1900). 

 3 F. Hofmeister, Ergebnisse der Physiol. I., i., p. 159 (1902). 



