( 345 ) 
at Klaten, that our researches were tending in many ways in the 
same direction, I terminated mine for the time being and I am post- 
poning the publication of various results until Mr. HAZEWINKEL 
shall have ended his researches, which are in many respects of impor- 
tance, and published the results of them. 
In the “Verslag” for 1891/2 it is stated that preliminary investi- 
gations into the preparation of indigo showed that the extraction 
of the leaves with water at the temperature prevailing here is not 
accompanied by evolution of gas during the time which in Java is 
considered needful to extract the constituents which yield the colour- 
ing matter from the plant viz: 6—7 hours. Later, for example in 
a day, this does occur. The gas evolved consists of carbon dioxyde 
and a gas which burns with a colourless flame, very probably hydrogen. 
What compound exists in the aqueous extract of the indigoleaves 
is not yet made out with certainty. It had a distinctly acid reaction ') 
and shows the so called indicanreaction very beautifully when it is 
shaken with hydrochloric acid, chloroform and air. 
The filtrate obtained after treating the extract with excess of lead 
acetate gives a yellow precipitate *) with ammonia, stated by Scnunck 
to be characteristic of indican. 
Since indigowhite is said to be insoluble in acid liquids, it is not 
very probable that this substance is present in the aqueous extract 
of the indigoleaves. A dilute solution of indigowhite in lime water 
behaves also in many respects quite differently from the extract. 
If the indigoleaves are extracted with dilute acetic acid (1 pCt.) 
instead of with water, the extract yields indigoblue abundantly when 
shaken with air, especially if ammonia is added.” 
According to Mr. v. LOOKEREN CAMPAGNE ®) the liquid produced 
by the so called fermentation is alkaline and contains indigowhite 
in solution. In the “Jaarverslag van ’s Lands Plantentuin” for 1893, 
the following is to be found: 
“The solution obtained by extracting indigoleaves with water for 
7 hours has again been the subject of an investigation, a few of the 
results of which will be indicated -here. ‘The liquid contained free 
1) That the extract of the indigo-leaves in acid is very easily shown by running it 
into a solution of potash coloured red by phenolphthalein. The reaction is also suc- 
cessful with a solution of blue litmus. (Note of 1892). 
2) I have found, subsequently, that an extract of the leaves of Zudigofera galegoïdes, 
which contains a substances resembling amygdalin, also gives a yellow coloured pre- 
cipitate in which, however, the glucoside has no part. 
3) Verslag omtrent onderzoekingen over Indigo, 1893, 16. 
