FORMATION OF INDIGO-BLUE. 1 9 1 



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 separated by filtra- 

 tion. The filtered liquid, which is brown, is to be further 

 evaporated until it leaves a thick brown syrup. 1'his 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 so- 

 lution there is now added several times its volume of ether. 

 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 ether, 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, however, be neces- 

 sary, this is best efi'ected by agitating the liquid in the cold 

 with hydrated oxide of copper. A green solution is ob- 

 tained which is filtered, and a current of sulphuretted hydro- 

 gen gas being passed through it, it is again filtered from 

 the precipitated sulphuret of copper, and evaporated either 

 spontaneously or in vacuo over sulphuric acid. This method 

 is attended with considerable loss, as the whole of the brown 

 syrup insoluble in ether, 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 ether in a displacement apparatus ; 

 distilling the greatest part of the ether; evaporating the 

 remaining 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 



