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A few Facts relative to the Colouring Matters of some Vegetables. 

 By James Smithson, Esq. F.R.S. Read December 18, 1817. 

 [Phil. Trans. 1818, j*. 1 10.] 



The author offers the scattered facts contained in this paper to the 

 notice of the Society, in the hope that they may induce some other 

 person to extend the experiments, interesting not merely in che- 

 mistry but also in the art of dyeing. 



The author observes that Fourcroy's opinion, that turnsole is red 

 originally, and made blue by carbonate of soda, is erroneous, for its 

 tinctures contain no alkali of any kind ; he found in it a small por- 

 tion of carbonate of lime. The insoluble part of turnsole is rendered 

 red by acids, but not affected by carbonate of soda ; when burned, a 

 portion of smalt remains. The soluble part was obtained by evapo- 

 rating its aqueous solution. When burned it leaves a little potash, 

 which the author thinks essential to its composition, and that, like 

 ulmin, it may be a compound of a vegetable principle with potash. 

 The next colouring principle noticed by the author is that of the 

 violet, it is reddened by acids, and becomes first green and then 

 yellow by the alkalies and the carbonates. A similar principle exists 

 in the petals of the red rose, of red clover, of the tips of the daisy, in 

 the blue hyacinth, hollyhock and lavender, in the inner leaves of the 

 artichoke, in the skin of plums, and in several other vegetable sub- 

 stances, also in the red cabbage. To this principle the author ap- 

 plies the name of Ajax, whose blood is fabled to have dyed the 

 violet. 



In sugar-loaf paper the author found two colouring matters : one 

 red, and soluble in water ; the other blue, and requiring an acid for 

 its extraction. 



The juice of the black mulberry is rendered green by caustic potash, 

 blue by carbonate of soda, and vinous red by carbonate of ammonia. 

 When mixed with chalk it rendered that substance blue, and the 

 filtered liquor was red, and could not be made blue by further addi- 

 tion of the chalk. Heat did not affect the red colour of this liquid. 

 If the red and the blue matter contained in the mulberry be con- 

 sidered as distinct principles, the author proposes to call the former 

 Pyramus, the latter Thisbe. 



The colouring matter of the corn-poppy is scarcely altered by car- 

 bonate of soda. Caustic potash makes it green, and caustic ammonia 

 produces no effect. Muriatic acid renders the infusion of the poppy 

 petals florid red, which is rendered dark red by carbonate of lime. 

 These and other experiments induce Mr. Smithson to regard the 

 colour of the corn-poppy as analogous to the red principle of the 

 mulberry. 



The pigment called sap green is the inspissated juice of the buck- 

 thorn berries. It is rendered yellow by carbonate of soda and caustic 

 potash. Its solution is reddened by acids, and the green is restored 

 by chalk. To this substance, and to the common green matter of 

 vegetables, the author assigns the name Chloris.. 



