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fact, that during the slowly dying of the leaves at the air, a consi- 
derable quantity of indoxyl is lost in an unknown way. And in 
this circumstance I see one of the reasons why, in woad-leaves, there 
is produced so much more indigo by the ,ammoniac-experiment” than 
by the ,alcohol-experiment”, because in the furmer the leaves die 
almost instantly, whilst the latter requires much more time. 
With Jndigofera, as said above, the ,alcohol-experiment’” produ- 
ces hardly any indigo. I have therefore tried to substitute for it a 
better one, which is effected in the following way, and by which, 
also excellent results are to be obtained with Polygonum. 
At the direct action of ammoniac, indican-plants form no indigo 
at all, for thereby not only the protoplasm is killed, but the 
indigo-enzyme, too, 1s so quickly destroyed that it cannot decompose 
the indican. But we can, before exposing to the alkaline vapour, 
decompose the indican and free the indoxyl, by making the plants 
die by complete exclusion of air, but which in this case should 
occur in such a way, that the indoxyl remains within the plant 
itself. Indican-plants turn then into „dead indoxyl plants’ and can 
in this condition, quite like the living woad, be subjected to the 
„ammoniac-experiment’’ with a very good result. 
The simplest way by far to reach the double aim of killing the 
plants by exclusion of air and leaving the indoxyl in the cells, is 
by entirely plunging them into mercury, whereby asphixion follows 
with surprising quickness, the protoplasm becoming permeable and 
the indigo-enzyme and the indican mixing together. At a proper 
temperature !) the indican is then decomposed after a few hours and 
the freed indoxyl remains in the leaf, albeit not exclusively in the 
cells in which originally the indican was localised. The leaf is then 
taken out of the mercury, ammoniac-vapour is allowed to act upon 
it, and at last the chlorophyll is extracted by boiling with alcohol 
and some hydrochloric acid. Even old Indigofera-leaves, which by 
the “alcohol-experiment’’ become quite colourless, take a brilliant 
blue colour by this “mercury-ammoniac experiment.” 
Before I had worked out the mercury-method, I examined the 
results of killing the leaves by the asphixion in hydrogen, carbonic 
acid and the vacuum, in each case followed, in the same manner 
as in the mercury-method, by subsequent exposition to ammoniac- 
vapour and extraction of the chlorophyll with alcohol. 
When the hydrogen was mixed with air a singular phenomenon 
1) The influence of temperature on (he action of the indigo-enzyme is interesting, 
I hope on another occasion to return to it, 
