32 Dr. Schunck on tlu; Furmatiun of Indiyo-blue. 



which is ])assc(l through a hair-sieve, in order to separate the 

 leaf-stalks and ribs of the leaves, and an extract of this powder 

 is then made in a displacement apparatus with cold alcohol in 

 the usual manner. The extract, which may be made stronger 

 by passing it through fresh quantities of powder, has a lively 

 dark green colour. It is evaporated in the a])paratus just de- 

 scribed, a little water being previously added to it, in order to 

 tacilitate the separation of the fatty matter. After a few hours, 

 there is found at the bottom of the evaporating dish a dark green 

 layer, consisting of fat and green colouring matter, covered by a 

 light brown watery liquid. The latter is poured off, filtered, 

 agitated with a quantity of fi-eshly precipitated oxide of copper, 

 and iiltered again. It now appears of a dark green colour from 

 oxide of copper in solution. The latter having been removed by 

 means of sul])huretted hydrogen, the filtered liquid, which is 

 now quite clear and of a light yellow colour, is evaporated again 

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

 s)Tup 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 more 

 fully described below. Tiie alcoholic liquid after being poured 

 off is mixed with about twice its volume of sether, when it becomes 

 milky and deposits a substance of a syrupy consistence, which 

 contains an additional quantity of the body just referred to, and 

 also some of the peculiar kind of sugar which is formed by the 

 decomposition of indican. After the mixture has stood for 

 several hours, there is usually found deposited on the surface of 

 the syrii]) and attached to the sides of the glass a quantity of 

 white crystalline needles, which also consist of a product of the 

 decomposition of indican. After the pethereal liquid has become 

 clear, it is poured on a filter and then evaporated as before, when 

 it leaves a clear brown syrup, consih.ting of indican in as high 

 a state of purity as I have been able to obtain it. The only 

 impurity which may still attach to the indican as thus prepared, 

 is a small quantity of fatty matter, the last traces of which it is 

 extremely difficult to remove. When an alcoholic extract of 

 woad is (■\aporated and water is added to the residue, the filtered 

 liquid, though it may appear tolerably clear, still contains a quan- 

 tity of fatty matter, in a state cither of solution or, as seems 

 more probable, of mechanical suspension. On adding acid to 

 it, this fatty matter separates in greenish masses, which melt 

 when the liquid is heated. The greatest part of this fatty mat- 

 ter is carried down by the oxide of copper used in the process 

 just described, :md the remainder is generally removed, when 



