itMATION OF INDIGO-BLUE. 185 



a powder, which is passed through a hair sieve, in order to 



separate the leaf-stalks and ribs of the leaves, and an extract of 



- then made in a displacement apparatus with cold 



alcohol in the usual manner. The extract, which may be made 



^er by passing it through fresh quantities of powder, 



I lively dark green colour. It is evaporated in the 

 apparatus just described, a little water being previously added 

 to it, in order to facilitate the separation of tne fatty matter. 

 After a few hours there is found at the bottom of the evapo- 



5 dish a dark green layer, consisting of fat and green 



colouring matter, covered by a light brown watery liquid. 



poured off, filtered, agitated with a quantity of 



iy precipitated oxide of copper, and filtered again. It 

 now appears of a dark green colour from oxide of copper in 

 solution. The latter having been removed by means of sul- 

 phuretted hydrogen, the filtered liquid, which is now quite 



and of a light yellow colour, is evaporated again in the 

 same apparatus, when it leaves a brown syrup. This syrup 

 contains besides indican some products of decomposition of the 

 latter. On being treated with cold alcohol only a portion of 

 it is dissolved, a part remaining undissolved in the form of a 

 brown glutinous substance, which is a product of the combined 

 action of water and oxygen on indican, and which will be 



winter, though the plant in the ensuing year teems to hare lost none of its 

 vigour, as may be seen by the size and abundance of rich glaucous leaves 

 which it puts forth, and the quantity of flower stems bearing numbers of 

 flowers, and then of seeds which it sends up, still the leaves are as poor in 

 colouring matter as those of the .preceding autumn. The inferior quality of 

 the dye produced from the second year's leaves, which in Thuringia went by 

 the name of "Kompts-waid" (see Schreber's Beschreibung des Waids) was 

 well known to the growers of woad in former times. 



Woad it still employed by the woollen dyers in this country, but what use- 



rpose it answers in preference to an equivalent quantity of indigo, I am 



unable to say. A specimen of the drug, as used by a woollen dyer, which I 



examined, contained no trace of indigo-blue. If its use be merely to act as a 



t and reducing agent on the indigo employed at the same time, as is 



obable, its place might be supplied by rotten cabbage leaves or decaying 



vegetable matter of any kind. 



2 B 



