388 
DR. C. B. PLOWRIGHT ON BRITISH DYE PLANTS. 
Society, W. Phillips, F.L.S., of Shrewsbury, Rev. Dr. Keith of 
Forres, and Rev. D. McDougal of Rothiemurchus, with specimens 
and materials for experiment. 
List of British Dye-Plants and results obtained. 
Thalictrum flavum. — Gives a poor yellow with alum. 
Caltha palustris.— The flowers, yellow with alum. 
Bf.rberis vulgaris. — The inner bark and the bark of the roots, 
yellow with alum. The colour is due to berberin. 
Nymph.ea alba. The rhizome gives a nice brown, with and 
without alum. This was found in use in the Hebrides, by Pennant, 
in 1782. 
Isatis tinctoria. — Is capable of yielding a number of colours. 
The flowers, with alum, dye wool a pale yellow. The fresh green 
leaves, boiled with wool, impart a reddish-brown to it. The blue 
colour, however, which is so essentially associated with Woad, is 
not readily yielded by it. This blue colour is really indigo, but it 
exists in the plant in such an unstable state that it can only be 
extracted with great difficulty. Its presence may however be 
demonstrated in the following manner : — Pour boiling water on 
fresh leaves of the first season’s plants. When cold, pour off the 
water, add a little caustic potash ; dip a piece of wool in this, and 
then immerse it in dilute hydrochloric or sulphuric acid. The wool 
will at once assume a more or less blue tint. The great difficulty 
is that the pouring off the infusion, and the dipping the wool into 
it, causes the unstable indoxyl, by the action of the air to pass into 
other products which are not indigo. For actual dyeing, the fresh 
green leaves are crushed into a pulp in a mill, the mass made into 
balls, which are dried; these are re-crushed, wetted, allowed to 
ferment, and finally made into a paste of a brownish hue, emitting 
a penetrating ammoniacal odour. The process of manufacture is 
given in full by Mr. Corder, in his excellent paper in the 
‘Transactions,’ 1890, vol. v. p. 144. The Woad in this state 
contains no indigo, but if it be mixed with water and maintained 
from fifteen or twenty hours at a temperature of 120° to 150° F., 
a certain amount of indigo is formed. The addition of a minute 
(Quantity of slaked lime, a mere trace, just enough to make the 
