84 Dr. Schimck on the Formation of Indigo-blue. 



but without any advantage resulting, as the substance was not 

 entirely removed from the rcthcr by means of water, a consider- 

 able quantity still remaining dissolved in the pether. 



111. The pounded woad leaves are extracted in a displacement 

 apparatus, as before, with cold alcohol. To the green alcoholic ex- 

 tract there is added an alcoholic solution of acetate of lead, which 

 produces a pale green precipitate,thc precipitation being then com- 

 pleted by the addition of a little ammonia. The precipitate, which 

 is bulky, is placed on a fdter and washed with cold alcohol, until the 

 percolating liquid instead of being dark green is only light gi'een, 

 and the excess of acetate of lead and ammonia have been removed. 

 It is then suspended in water, and a current of carbonic acid gas 

 is passed through the liquid. The precipitate gradually becomes 

 paler in colour and at last almost white, and loses considerably 

 in bulk, while the liquid acquires a yellow colour. The latter 

 being filtered, sulphuretted hydrogen is passed through it to 

 precij)itate a little oxide of lead contained in it, and being again 

 filtered is evaporated as before, either in the air or in vacuo over 

 sulphuric acid. 



Of these three methods I prefer the last, as being more expe- 

 ditious than the first and less costly than the second. One pre- 

 caution must not be forgotten, that of never in the last instance 

 attempting to evaporate the solution at a higher temperature 

 than the ordinary one. If the attempt be made, the substance 

 will undergo an entire change, as I have repeatedly discovei'ed 

 to my cost. This change consists in the substance taking up 

 the elements of water. It takes place as well in vacuo as in the 

 air. I have no reason to believe that the oxygen of the atmo- 

 sphere has any influence in producing decomposition, at least at 

 the usual temperature; and though I have generally in the last 

 instance evaporated in vacuo, I think the evaporation may just 

 as well be conducted in the air. Notwithstanding all precau- 

 tions, however, it is difficult to avoid some portion of the sub- 

 stance becoming changed during evapoi'ation. 



The body, the preparation of which I have just described, I 

 propose to call Indican^-. By evaporation of its watery solution, 

 it is obtained in the form of a yellow, transparent, glutinous 

 residue, which can only be rendered dry by spreading it out in 



* As the termination an has not yet been apphed by chemists to desig- 

 nate any peculiar class of bodies, I jiropose to restrict it to the names of 

 such substances of a complex constitution, like rubian, as are direct pro- 

 ducts of the vital energy of plants or animals, and which by their decom- 

 )30sition give rise to one or more series of organic compounds of a simpler 

 constitution. In applying it, it will of course be necessar)' carefully to 

 ascertain that the substance to be named is really a proximate constituent 

 of some organism, and not itself the result of any process of decomposition 

 either within or out of the organism — that it is an educt and not a product. 



