Dr. Schunck on the Formation of Indigo-blue. 83 



allowed to remain exposed to the atmosphere they attract moist- 

 ure again, and become flaccid and difficult to pulverize. The 

 powder must be kept warm until it is used. 



I. The leaves thus reduced to powder, being put in a displace- 

 ment apparatus, such as is used for the preparation of tannic 

 acid, are extracted with cold alcohol. The percolating liquid is 

 dark green. The extraction is continued until the liquid runs 

 through of a light green colour. The alcoholic extract is now 

 distilled in a retort, until a great part of the alcohol has passed 

 over; it is then evaporated in a basin at a moderate temperature. 

 During evaporation, a large quantity of chlorophyll and fatty 

 matter separates as a green glutinous mass, which is to be sepa- 

 rated by filtration. The filtered liquid, which is brown, is to be 

 further evaporated until it leaves a thick brown syrup. This 

 syrup, being poured into a flask, is redissolved in warm alcohol, 

 which it does with some difficulty, on account of the change 

 which the substance has undergone in consequence of the heat 

 employed in distilling the alcohol. To the warm solution there 

 is now added several times its volume of aether. The ?ether 

 renders the solution milky, and precipitates a large quantity of 

 matter, which collects at the bottom of the flask into a dark 

 brown syrup. After this syrup has completely settled, the sether, 

 which is also dark brown, is distilled. When the greatest part 

 has distilled over, water is added to the syrupy residue. A 

 quantity of brown fatty matter is precipitated, which is filtered. 

 The filtered liquid is light yellow, and contains the substance 

 almost in a state of purity. Should a further purification, how- 

 ever, be necessary, this is best eiFected by agitating the liquid in 

 the cold with hydx'ated oxide of copper. A green solution is 

 obtained, which is filtered, and a current of sulphuretted hy- 

 drogen gas being passed through it, it is again filtered from the 

 precipitated sulphuret of copper, and evaporated either sponta- 

 neously or in vacuo over sulphuric acid. This method is attended 

 with considerable loss, as the whole of the brown syrup insoluble 

 in aether, the quantity of which is not trifling, is formed at the 

 expense of the indigo-producing body. 



II. The second method consists in simply extracting the 

 pounded woad leaves with sether in a displacement apparatus, 

 distilling the greatest part of the aether, evaporating the remain- 

 ing green liquid at a moderate temperature, adding a little cold 

 water to the syrupy residue, separating the insoluble chlorophyll 

 and other matters by filtration and evaporating the yellow liquid 

 as before, cither spontaneously in the air or in vacuo. If puri- 

 fication should be necessary, it is effected, as in the preceding 

 case, by means of oxide of copper. I endeavoured to modify 

 this method by agitating the setherial extract with cold water, 



