( 124 ) 
As soon as the liquid becomes alkaline, however feebly, the 
indoxyl oxidises at the air with much greater quickness to indigo-biue. 
The statement of BrÉAUDAT !), that in the sap of Jsatis 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 indigo-blue from indoxyl. For, by 
preparing from the woad-leaves “crude enzyme” by finely rubbing 
them under, and extracting them with strong alcohol, whereby, after 
pressing and drying, a completely 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 2), 
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 substance which gives rise to a total destruction of 
the indoxyl, yet about the nature of it I cannot express a sup- 
position. 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 Indigofera this 
destructive influence is so strong that the ,alcohol- EPE of 
which later, wholly fails with this plant. 
Einen -superoxyd, too, causes the indoxyl gradually to vanish 
from the solutions, 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 sub- 
stance constantly changes into a brownish-black matter. 
In feebly alkaline and in moderately acid solutions, indoxyl, war- 
med with isatine gives, in absence of air, a precipitate of indigo-red, 
which is isomeric with indigo-blue 
C* H7 NO + CS HNO? = 0" Hie N20? + H20 
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 
1) Comptes rendus T. 127, pag. 769, 1898 en T. 128, pag. 1478, 1898. 
2) In a small porcelain vessel the menise of the fluid furthers the oxidation of 
indoxyl to indigo-blue just in the same way as vcrude-enzyme”, strewed as a powder 
on the surface of the liquid, 
