INDOXYL-SULPHURIC ACID. 693 



analogous blue or green pigments are produced only from those derivatives 



CH CH 



of indol which, like n-methyl indol C 6 H 4 <^\CH, a-naphtmdol,C 10 H 8 <^\CH or 



N.CH, NH 



N.CH, 

 CH 2 



n-methyl indolin, C 6 H 4 <T >CH 2 , do not have the hydrogen atoms of the two 



N.CH 3 



methine groups substituted by alkyl. From those derivatives in which one or two 

 hydrogen atoms are substituted by alkyl, such as a-methyl indol, dimethyl indol, 

 C.CH 3 CH 



C 8 H 4 <^Sc.CH 3 , and bz. 3, pr. 2-dimethyl indol, CH 3 . CeH/\C.CH 3 , red pigments 



NH NH 



are produced, a behavior which PORCHER and HERVIEUX * have observed in several 

 alkyl-substituted indols. 



An increased elimination of indican has been observed in many 

 diseases, 2 and in these cases the quantity of phenol eliminated is also 

 generally increased. A urine rich in phenol is not always rich in indican. 



The potassium salt of indoxyl-sulphuric acid, which was prepared 

 pure by BAUMANN and BRIEGER from the urine of a dog fed on indol, 

 has subsequently been prepared synthetically by BAUMANN and THESEN, S 

 by fusing phenyl-glycine-orthocarboxylic acid with alkali and then from 

 this producing the indoxylsulphate by means of potassium pyrosulphate. 

 It crystallizes in colorless, shining plates or leaves which are easily soluble 

 in water, but less readily in alcohol. It is split by mineral acids into 

 sulphuric acid and indoxyl. The latter without access of air passes into 

 a red compound, indoxyl red, but in the presence of oxidizing reagents 

 is converted into indigo blue: 2C 8 H 7 NO + 2O = Ci 6 HioN 2 O2 +2H 2 O. The 

 detection of indican is based on this last fact. 



For the rather complicated preparation of indoxyl-sulphuric acid as 

 potassium salt from urine the reader is referred to other text-books. 

 For the detection of indican in urine in ordinary cases the following 

 method of JAFFE-OBERMAYER, which also serves as an approximate test 

 for the quantity of indican, is sufficient. 



JAFFE-OBERMAYER'S Indican Test. JAFFE uses chloride of lime as 

 the oxidizing agent, while OBERMAYER employs ferric chloride. Other 

 oxidizing agents have been suggested, such as potassium permanganate, 

 potassium dichromate, alkali chlorate, and hydrogen peroxide (the 



1 The work of Porcher and Hervieux can be found in Compt. rend., 145, Compt. 

 rend. soc. biol., 62, and Bull. soc. chim. (4), 1; Benedicenti, Zeitschr. f. physiol. Chem., 

 53 and Arch. f. exp. Path. u. Pharm., 1908, Suppl. (Schmiedeberg's Festschr.). 



2 See Jaffe, Pfluger's Arch., 3; Senator, Centralbl. f. d. med. Wissensch., 1877; 

 G. Hoppe-Seyler, Zeitschr. f. physiol. Chem., 12 (contains older literature); also Berl. 

 klin. Wochenschr., 1892. 



3 Baumann with Brieger, Zeitschr. f. physiol. Chem., 3; with Thesen, ibid., 23. 



