FROM THE POLYGONUM FAGOPYRUM. 123 
to the same genus, the Polygonum tinctorium, is remark- 
able for the large amount of indigo-blue which it affords. 
Nevertheless on submitting the leaves of the plant to the 
same process as that previously employed in the case of 
the Isatis tinctoria and other plants producing indigo, I was 
unable to obtain a trace of that or any other blue colouring 
matter. The examination led, however, to the discovery 
of a crystallised yellow colouring matter, the method of 
preparation and properties of which I shall now proceed to 
describe. 
The plant, which is one easily cultivated and will grow 
in the poorest soils, having been allowed to attain its full 
size, the leaves are separated from the stalks, and treated 
for some time with boiling water. The decoction, which 
is muddy and of a greenish colour, is strained through 
calico, and the mass remaining behind is well pressed in 
order to remove all the liquid. A little acetate of lead is 
now added to it. This produces a bulky yellowish-green 
precipitate, consisting of chlorophyll and other impurities 
in combination with oxide of lead. Care must be taken to 
add only so much acetate of lead as to render the super- 
natant liquid clear and transparent, as an excess would 
precipitate a portion of the colouring matter. The liquid, 
having been again raised to the boiling point, is filtered 
boiling. It has a fine golden yellow colour, but on being 
mixed with a quantity of acetic acid it becomes pale 
yellow, and on being now allowed to stand for some time it 
deposits a voluminous mass of small yellow crystalline 
needles. These are collected on a filter, slightly washed 
with cold water and then re-dissolved in boiling water, to 
which a little acetic acid is added. A small quantity of 
white matter is usually left undissolved, which is separated 
by filtration. The filtered liquid again deposits, on cooling 
and standing, a mass of crystals, which, after being col- 
