1 82 Mil. E. SCHUNCK ON THE 



leaves of the Polygonum with ether, taking care to exclude 

 the air, until the green colour had changed to white, when, 

 on exposure to the atmosphere, they speedily became blue. 

 Robiquet,* Colin, f Turpin,j: and Joly,|| on the other hand, 

 expressed a very decided conviction, that indigo-blue pre- 

 exists in the Polygonum tinctorium, but not in a free state ; 

 that it is combined with some organic substance or sub- 

 stances, which render it soluble in water, ether, and alcohol ; 

 and that it requires the operation of potent agencies in order 

 to destroy this combination and set the indigo at liberty. 

 Osmin Hervey,§ in a memoir on the Polygonum tinctorium, 

 which in some parts is rather obscure, inferred from his 

 experiments: 1. That indigotine exists in the leaves of 

 this plant in a state of combination with a resin. 2. That 

 this natural compound of indigo and resin contains both 

 white indigo and blue indigo, and of the latter a larger 

 proportion the older the leaves are. 3. That by the influ- 

 ence of certain organic substances, the indigo-blue is again 

 reduced to the colourless state, if the solution be effected 

 by means of water, without any destruction of the natural 

 compound taking place. Girardin and Preisser^ again re- 

 turned to Chevreul's view, that the colouring matter is 

 contained in the leaves of this plant in the form of reduced 

 indigo. Since the publication of these treatises, no new 

 ideas have, as far as I know, been promulgated by chemists 

 in reference to this subject.** 



• Journal de Pharmacie, T. XXV., p. 62. 



-|- Memoire sur la Renouee des Teinturiers. Paris, 1839. . 

 t Etudes microscopiques sur le gisement de la matiere bleue daus les feuilles 

 du Polygonum tiuctoriuno, Memoire lu a I'Academie des Sciences le 12 Novem- 

 bre, 1838. 



11 Observations generales sur les plantes qui peuveut fournir des couleurs 

 bleues h la teinture. Montpellier, 1839. 



§ Journal de Pharmacie, T. XXVI., p. 290. 

 t Ibid, p. 344. 



• • I cannot refrain from expressing on the present occasion my regret, which 

 it probably shared by many others, at the want of a general chemical bibli- 



