1818.] colouring Constituent of Roses. 297 



subsequent experiments ; and if it, be considered how very 

 inconsiderable a portion of this metal communicates a blue 

 colour to the sapphire and a red colour to the ruby, it is hardly 

 possible to conceive that any notable portion of it can exist- 

 in the flowers and leaves of plants without being manifested by 

 some of the various hues by which the metal is characterized in 

 its different combinations, when acted upon by light, heat, and 

 atmospheric air. 



Before I proceed to detail any of these experiments, it is proper 

 to notice some very powerful objtctions which have occurred 

 respecting the presence of iron in the precipitate which I ob- 

 tained from the infusion of roses, by means of ammonia, as men- 

 tioned in my last ; of which I transmitted a portion to you, and 

 to other eminent chemists, socn after the publication of my 

 former letter. This precipitate was found to burn to a white ash, 

 in which no portion of iron could be detected sufficiently consi- 

 derable to entitle it to the distinction of a colouring agent ; and 

 hence it was inferred, as a probable conjecture, that the metallic 

 iron, which I sent also to you, was due to the prussiated alkali 

 used in the experiment. In answer to which, it may be urged 

 that we must cease to employ this re-agent as a test of the pre- 

 sence of iron, if the mere touch of a glass rod, dipped in a solu- 

 tion of prussiate of potass, be capable of communicating such a 

 considerable portion of the metal, to fluids before destitute of it, 

 as to account for the metallic and magnetic beads exhibited to 

 you, and which were obtained from such inconsiderable volumes 

 of a solution as test-tubes are fitted to contain. But 1 trust I shall 

 be able to show, that the iron is really due to the vegetable infu- 

 sion to which it was ascribed ; having, by means of other tests 

 and other experiments, not liable to these objections, obtained 

 the same results ; not only from the petals of roses, but from the 

 leaves of plants, and from flowers of all colours. It must 

 remain, therefore, for your chemical readers to determine, 

 whether iron, existing under such various modifications, and 

 differing only as to its quantity, however decisively its presence 

 may be demonstrated, ought to be considered as having any 

 connexion with the colour of the vegetable in which it resides. 



(A.) — The colouring principle in vegetable extracts, whatever 

 be its nature, being soluble in water, as admitted by Chaptal* 

 and also by Thenard,f with whose observation I terminated the 

 last communication 1 made to you upon the subject, I resolved 

 to try an experiment with the petals of the damask rose, using 

 no other solvent than water. For this purpose, I made an infu- 

 sion, Ity boiling distilled water in a Florence flask, and pouring 

 it, in a boiling state, upon a quarter of a pound of the dried petals, 



• " Nothing more is necessary than to infuse these substances in water, for the 

 purpose of extra, ting their colouring piinciple." — ChaptaCs Chemiftry, vol. iii. 

 p. 151, London, 1795. 



t Traite" de Chimie, tome troisieme (1716), p. 316. Paris, 1815, 



