142 OXYPROTEIC ACIDS 



means of copper acetate, with subsequent dissociation of the 

 copper compound by sulphuretted hydrogen, is nothing but 

 an oxydation transformation product of the true urochrome. 

 Browinski and Dombrowski 62 in their most recent publica- 

 tion with special stress suggest "that urochrome is an un- 

 usually easily decomposable compound and readily under- 

 goes oxidation. Its precipitation from the urine and from 

 pure solutions by means of cupric acetate is due to the forma- 

 tion of a cuprous compound which is soluble in water ; and 

 can occur only with reduction of the copper acetate. The pre- 

 cipitation is therefore incomplete, because necessarily the 

 combination is formed with oxidation of a portion of the 

 urochrome. ' ' Thus far it is possible to agree with the Polish 

 authors. But with their further statement the author's 

 views become directly opposed: "The oxidation product (of 

 the urinary coloring matter) which remains in solution im- 

 parts the faint yellow tint to the nitrates of copper precipita- 

 tion peculiar to them. ' ' According to this the substance in the 

 nitrate would be an insignificant remnant of the true urinary 

 coloring matter which has escaped precipitation and has 

 undergone oxidation. Actually, however, as Weiss has 

 shown in his colorimetric estimations, 63 the opposite is the 

 case. If Dombrowski 's urochrome (a sallow brownish 

 yellow coloring substance) be removed, by far the greater 

 part of the coloring matter remains in the filtrate, which 

 shows the characteristic pure tint (yellow with a greenish 

 cast) of the former [true urochrome]. Any unprejudiced 

 person must grant that when one knows that a given sub- 

 stance is very ready to undergo oxidation there is little 

 propriety in using an oxidizing agent like copper acetate in 

 isolating it. If, however, such an agent is employed and, 

 too, if it has been clearly proved that oxidation has actually 



62 J. Browinski and S. Dombrowski (Instit. of Med. Chem., Lemberg), 

 Zeitschr. f. physiol. Chem., 77, 105, 1912. 



88 M. Weiss, Biochem. Zeitschr., 30, 340, 1911. 



