330 



of Polygonum iinclorium '), for which latter plant the same fact as described by Al- 

 \arez, has also been established by Molisch -). 



So it was evident that the indigo-plants must belong to two physiologically dif- 

 ferent groups, and I subjected the concerned chromogenes to a further examination 

 with the following results. 



I. The Chromogene of the Indigo-f'lants is I ndoxyl ar hidican. 



The chromogene of woad is not as is usually accepted indican, but the very in- 

 stable indoxyl C'H'NO. Indigofera leptostachya and Polygonum tinctorium, on the 

 contrary, contain the constant glucoside indican, the constituents of which are, in 

 accordance with the supposition of Marchlewski and Radclifïe ^), indoxyl and sugar, 

 which has first been brought to certainty by Mr. Hazewinkel, and, without my know- 

 ing of his experiments, by myself. Woad, as an »indoxyl-plant« containing no in- 

 digo-glucoside, wants also an enzynie to decompose it. The two mentioned »indican- 

 plants«, on the other hand, do contain such an enzyme, which had already in 1893 been 

 rendered probable by Mr. van Lookeren Campagne with regard to Indigofera^). I 

 have prepared this enzyme, albeit in a very impure state, in rather great quanlity and 

 1 hope afterwards to describe the experiments made with it. 



The important difference between »indoxyl-« and »indican plants« beconies parti- 

 culary clear when comparing the different extraction methods. Thereof what follows. 



If »indican-plants« are extracted with water below tlie temperature at which the 

 indigo-enzyme becomes inactive, for instance below 40" C. or 50° C. (»cold extrac- 

 tion»), and under careful exclusion of air, an indoxyl-solution is obtained. If, however, 

 the same »indican-plants« are extracted by boiling (»decoction«), the indigo-enzyme 

 will be destroyed, and independently of renioval or access of air, an indican-solution 

 results, which can be kept perfectly unchanged when microbes are excluded, but either 

 by the separately prepared indigo-enzyme, or by certain bacteria or yeasts, or also by 

 boiHng with acids, it can be converted into the constituents indoxyl and sugar. I have 

 prepared from it the crude indican in a dry state, by evaporating to dryness the 

 decoctiiins of both Indigofera leptostachya and Polygonum tinctorium. The brown 

 matter, thus produced, resembles sealing-wax, is very brittle and can quite well be 

 powdered. 



') Mucli niaterial of this Indigofera, as well l'iill Krown plants as secds. I o\\ c to 

 tlic kindness of Mr. van Lookeren Campagne of Wagcningcn. This interesting 

 plant, a native of Natal, has been cultivatcd, very rich in indican, in the open ground 

 in the I.aboratory-sardcn at Delft: at Waneningi'ii sevrrnl specimens liad (irown this 

 summer to more than 1.5 M. lieiKlit. 



Polygonum tinctorium comes from Cliina .iiid is, as tlu- \s(ia(l, in the secd-commercc 

 of Vilmorin in Paris. 



') Sitzungsber. d. Akad. d. Wissensch. zu Wien. Math. Natiiru. Klasse, Bd. 107, 

 pag. 758, l8()8. 



') Journ. Soc. for chcni. Industry, T. 87. pag. 430, 1898; Chem. Ccntralblatt, Bd. 65, 

 pag. 204, i8()8. With thankfnlness I rcmcmbcr the aid Icnt me by my chcniical colleagues 

 Hoogewerff and Behrcns in the determination of in<lo.xyl 



*) Verslag omtrent onderzoekingen over indigo, pag. i_>, .Sainarang iSoj. 



