DR. EDWARD SCHUNCK ON INDIGO-BLUE. 223 



dried in a stove moderately heated, and, while still warm, 

 ground to powder. The powder, which had the colour of 

 fresh hay, was passed through a hair sieve to separate the 

 leaf-stalks and other fibrous portions, and then extracted 

 in a percolator with spirit of wine. The green alcoholic 

 extract was evaporated in a shallow tin dish, the evaporation 

 being assisted by passing a current of air over the surface 

 of the liquid in the apparatus formerly described. Chlo- 

 rophyll and fatty matter were deposited during evaporation, 

 leaving a brown watery liquid, which was poured off, agi- 

 tated with freshly precipitated copper oxide, and filtered. 

 The copper in the filtrate was precipitated with sulphu- 

 retted hydrogen, and the filtered liquid was evaporated 

 as before. The residue was treated with absolute ether, 

 which dissolved a portion, and left, on evaporation, a yel- 

 low sirup. This sirup is the indigo-producing body as 

 pure as it is possible to obtain it. I prefer to this the 

 following process, as being more expeditious and surer. 

 The alcoholic extract of the dried leaves having been eva- 

 porated, thewatery liquid which is left is mixed with acetate- 

 of-lead solution, which gives a dirty-yellow precipitate, con- 

 sisting of chlorophyll and other impurities in combination 

 with lead . To the clear yellow filtrate basic lead acetate is 

 added ; this gives a primrose-yellow precipitate, which is 

 filtered off and, after being washed with water and then 

 with alcohol, is suspended in absolute alcohol, through 

 which a current of carbonic anhydride is passed. After 

 the gas has passed through for some time the liquid acquires 

 a yellow colour, and, after being filtered from the insoluble 

 portion, consisting principally of lead carbonate, is evapo- 

 rated at the ordinary temperature. Water added to the 

 residue leaves a portion undissolved, which is filtered oft". 

 Sulphuretted hydrogen is passed through the filtrate to 

 precipitate the lead contained in it ; and having been again 



