(193) 
water is poured in, the leaves are pressed together until all air is 
replaced, and the stopper is put on so as not to leave the smallest 
air-bubble. By the exclusion of the air, together with the high tem- 
perature, the leaves soon die and already after a few hours a clear, 
light yellow liquid can be decanted, which is rich in indoxyl. If 
some alkali is added and air blown through, the indigo-blue precipi- 
tates, the colour of which appears only pure after acidification. In 
a sufficient time of extraction there can be thus obtained from woad 
a liquid of which the proportion of indoxyl, according to RriNwarpr !) 
who in 1812 applied the decoction-method on a rather large scale, 
answers to 0.3 pCt. “pure indigo” for the fresh leaves, which, as 
he remarks, might rise to the double amount in the South. If we 
consider that the indoxyl is especially concentrated in the youngest 
organs still in a state of cell-partition, that it diminishes considerably 
in full grown parts, and is almost or wholly absent in old leaves, 
we must conclude that the youngest organs may contain more than 
0.3 pCt indigo. As the woad-leaves contain about 85 pCt water 
this would correspond to a little less than 2 pCt indoxyl in the 
dry matter *). 
The indoxyl-eontaining sap, whether prepared by “cold extraction” 
from the indican-plants or by decoction from the indoxyl-containing 
woad, has the following characteristics. It is a light yellow, in cold 
greenish fluorescent fluid; at warming the fluorescence dim‘nishes and 
comes back at cooling. The reaction is feebly but distinctly acid, 
of course not by the neutrally reacting indoxyl but by organic acids. 
At the air a copper-red film of indigo-blue is formed at the surface 
of the liquid. 
2(CSH7NO) + 0? = C16 HY N202 + 2 H°O, 
but this oxidation follows so slowly in the feebly acid solutions, 
that evaporating to dryness at the air is possible without too much 
loss of indoxyl. The indoxyl itself is soluble in water, ether, alco- 
hol and chloroform, in the two last under slow decomposition when 
the air finds access. 
1) In a report of 6 December 1812 to the President of the Agricultural Comittee 
for the Department of the Zuiderzee, present as a manuscript in the library of the 
Academy of Sciences, Amsterdam, 
2) But according to GrorcEvics, Der Indigo, pag. 2 and 18, Wien 1892, the rate 
of indigo for woad would only amount to 0.05 pCt, In my laboratory Mr. van HassELT 
found in three special cases 0.05 pCt, 0.07 pCt. and 0.09 pCt. indigo-blue in 
relation to the weight of the living leaves, which latter amount corresponds to c.a 
0.6 pCt indoxyl with regard to the dry weight. 
