Further researches on the Formation of Indigo 

 from the Woad (Isatis tinctoria). 



Proceedings of the Section of Sciences, Kon. Akademie van Wetenschappen, Amsterdam, 

 Vol. Ill, 1900, p. 101 116. Verscheen onder den titel Verdere onzoekingen over 

 de indigo-vorming uit Weede (Isatis tinctoria)* in Verslagen Kon. Akademie van We- 

 tenschappen, Wis-en Natuurk. Afd., Amsterdam, Deel IX, 1900, biz. 7490. 



Since my first communication on the chromogene of the woad 1 ) I have found 

 that the indoxyl does not exist in it in a free condition, as I then thought, 

 but in a loose compound which I will call isatan, and which, by an enzyme, 

 simultaneously present, the isatase, is easily decomposed with production of indoxyl. 



/. The research of Schunck. 



As soon as I had come to this conclusion, the question arose, whether the 

 matter prepared by Schunck from the woad in 1855, and described 2 ) under 

 the name of indican, can be either or not identic with isatan. That in many 

 of his experiments he has indeed had isatan before him I consider as certain. 

 But in carefully reading his essay I met with number of contradictions, which 

 are only to be explained by Schun ck's working with two other substances besides, 

 which he continually interchanges with each other and with isatan ; these are 

 indoxyl and a chromogene which colours intensely yellow by alkalies, occurs 

 abundantly in the woad, precipitates, just like isatan, with basic lead acetate, but 

 has nothing to do with indigo. If I well understand him he calls this substance 

 changed indican and considers that it differs from it by containing one or two 

 H 2 O more, but this is a wholly unproved hypothesis. 



Indoxyl was not known to Schunck at all, but his second preparation 

 method of the indican reposes on ether extraction of jthe dried plant. As isatan 

 is not soluble in ether I suppose that during the preparation small quantities of 

 indoxyl originated from the isatan, which easily occurs under various influences, 

 and for which ether is an excellent solvent. 



However strange it may be, it was the matter colouring yellow by alkalies, 

 and not the indigo-chromogene itself, which Schunck subjected to the three 

 analyses on which reposes the well-known formula of the woad-indican. Quite 



! ) On the Formation of Indigo from the Woad (Isatis tinctoria). Kon. Akad. van 

 Wetenschappen, Amsterdam; Proceedings of the Meeting of 3oth September 1899. 



2 ) E. Schunck. On the Formation of Indigo-blue. Parti. Philosophical Magazine 

 (4) Vol. 10, pag. 74, 1855. For the indiglucine: Ibid. Vol. 15, pag. 127, 1858. 



M. W. Beijerinck, Verzamelde Geschriften ; Vierde Deel. I 



