140 
DR. C. B. PLOWRIGHT ON WOAD AS A BLUE DYE. 
a condition known as indigo-brown, in which an insoluble black- 
brown substance is formed which is useless to the dyer, and cannot 
be re-converted into indigo blue. During the unsettled state of 
Europe towards the end of the eighteenth and beginning of the 
nineteenth century, numerous attempts were made to manufacture 
indigo directly from Woad ; prizes were offered by various govern- 
ments for the attainment of this object in order that the use of 
foreign indigo might be obviated, as it could only be obtained 
with difficulty. None of these processes were ever practically 
successful.* Many of them were entirely theoretical. Some sought to 
obtain indigo by macerating fresh Woad leaves in cold water, others 
in warm water, others infusing them in boiling water, and sub- 
sequently washing with cold. 
The full details of these essays are given by Giobert,f who with 
Du Puymaurin,j; came nearest success. 
To demonstrate the presence of indigo in the Woad leaf, the 
process of Dr. Hans Molisch§ is the best. This consists in keeping 
the fresh leaves in a wide-mouth stoppered bottle, filled with 
gaseous ammonia for twenty-four hours, and then dissolving out the 
chlorophyl by immersing the leaves for a like period in absolute 
alcohol. Sections show that the indigo is confined to those tissues 
which contain chlorophyl, and that the hairs, cuticular cells (except- 
ing the guard cells of the stomata), and fibro-vascular bundles are 
free from it. When the chlorophyl has been thus extracted, the 
leaves have a blue colour of greater or less depth according to the 
amount of indigo they contain. 
Although the extraction of indigo is so difficult and unsatisfactory 
a process, yet Woad has been used as a blue dye from remote antiquity. 
* Amongst these suggested processes were those of the German chemist 
Justi; Astruc, 1737; Hellot, 1750; Borth, 1764; Kulenkamp, 1755; 
Eddel, 1756; Morrina, 1791; Nazarow, 1810; Dambournay, Pavie, 1811; 
Cioni, 1812 ; Michelotti, 1811 ; Bonfico, Heinrich, 1812 ; Du Puj-maurin, 
1810 — 1812; Giobert, 1813; Reinwardt, 1812. 
t Giobert. ‘ Traite sur le pastel,’ Paris, 1813, 8vo. 
t De Puymaurin. ‘ Sur le Pastel : sa culture et les Moyens d’en retirer 
l’indigo,’ 1810, 8vo. 
§ Molisch Hans. “Ueber das Vorkommen von Indican in Chlorophyllkorn 
der Indicanpflantzen.” Bericht der Deutsch. Bot. Gesell. 1899. Bd. xvii. 
Hf. 6, p. 228, t. xviii. 
