332 



soluble in water, ether, alcohol anti chloroform, in the two last under slow decom- 

 position when the air finds access. 



As soon as the liqiiid becomes alkaline, however feebly, the indoxyl oxidiscs at 

 the air with murh greater quickness to indigo-blue. 



The statement of Bréaudat '), that in the sap olfsalis there would be present an 

 oxidase, by which this oxidation is effected, is not proved ; in none of the three indigo- 

 plants I have been able to find an oxidase producing-blue from indoxyl. For, by pre- 

 paring from the woad-leaves »crude enzyme« by finely rubbing them under, and ex- 

 tracting them with strong alcohol, whereby, after pressing and drying, a completelv 

 colourless powder is obtained in which all the enzymes must be present, it is found 

 that the oxidising effect of this »crude enzyme« on an indoxyl-solution is very slight, 

 ceases soon, and does not change by boiling, from which must be concluded that the 

 oxidation cannot be attributed to oxidase, but is of a purely physical nature °). 



The leaves of the indican-plants give quite the same result. 



Though there originates during the slowly dying of woad-leaves at the air, a sub- 

 stance which gives rise to a total destruction of the indoxyl, yet about the nature of 

 it I cannot express a supposition. If it might prove to belong to the group of the 

 oxidases, it is surely in no other relation to the formation of indigo from indoxyl, than 

 that it is very pernicious to it. For the indican-plants the same has been observed. 

 In hidigofera this destructive influence is so strong that the »alcohol-experiment«, of 

 which later, wholly fails with this plant. 



Hydrogen-superoxyd, too, causes the indoxyl gradually to vanish from the So- 

 lutions, without any coloured products originating. 



Strong acids, just as alkalis, though in far less degree, favour the formation of 

 indigo from indoxyl, but then part of this substance constantly changes into a brown- 

 ish-black matter. 



In feebly alkaline and in moderately acid Solutions, indoxyl, warmed with isatine 

 gives, in absence of air, a precipitate of indigo-red, which is isomeric with indigo-blue 



This precipitate separates quickly out of alkaline solutions as fine red, from acid 

 ones as coarser dark crystal-needles and can easily be filtered. It is soluble in alcohol 

 and so can be separated from the indigo-blue. On warming an indican solution with 

 isatine and dilute hydrochloric acid, all the indoxyl which is set free precipitates as 

 indigo-red, and I presume that a good quantitative indican determination may be based 

 upon this reaction. 



All the here mentioncil characteristics of the indoxyl-containing plant-saps are 

 also announced in the literature of the chemically prepared indoxyl, except the con- 

 cluct towards isatine and hydrochloric aciil which lias pcrhaps not been exarained. 



Natural indigo prepared from woad, contains a small quantity of indigored ; but 

 whether this originates from the same indoxyl as the blue, or from an isomeric indo- 



') Comptcs rciidus, T. 127, pag. 769, 1898, en ']". ij8, pag. 1478. 1898. 



') In a small porcc-lain vcsscl the nicnisc of thu fliiid furlhcrs the oxidation of 

 indoxyl to indigo blue jiist in tlie sanit- way as »criHli-enzynic«, strewcd as a powder 

 on the surface of the liyiiid 



