VIII] AROMATIC COMPOUNDS 111 



give green or brown colorations. With lead, insoluble salts are formed. 

 Several of the members are powerful yellow dyes, and hence some plants 

 in which they occur, such as Ling {Erica cinerea), Dyer's Weld or 

 Rocket (Reseda luteola), have been used for dyeing purposes. The value 

 of these colouring matters as dyes has led to their chemical investigation, 

 and as a result the constitution, etc., of the hydroxy-flavones and flavonols 

 is well established. 



Ejcpt. 107. Demonstration of the presence offlavone or flavonol pigments in tissues 

 without chlorophyll. Take flowers of any of the undermentioued species and put them 

 in a flask with a few drops of ammonia. They will rapidly turn yellow owing to the 

 formation of the intensely yellow salt of the flavone or flavonol pigments present 

 in the cell-sap. If the flowers are next treated with acid the yellow colour will dis- 

 appear. 



Also make an extract of some of the flowers with a little boiling water. Filter, 

 cool and add the following reagents : 



{a) A little alkali. A yellow colour is produced. 



(h) A little ferric chloride solution. Either a green or brown coloration is produced. 



(c) A little basic lead acetate solution. A yellow precipitate of the lead salt of 

 the flavone or flavonol pigment is formed. 



The flowers of the following species can be used : Snowdrop {Galanthus nivalis)^ 

 Narcissus {Narcissus poeticus), white variety of Lilac {Syringa vulgaris)^ Hawthorn 

 {Crataegus Oxyacantha), White Lily {Lilium candidum\ white var. of Phlox, double 

 white Pink, white Stock {Matthiola) etc., etc., in fact almost any species with white 

 flowers or a white variety. 



Expt. 108. Demonstration of the presence of flavone or flavonol pigments in tissues 

 containing chlorophyll. Make a hot water extract of the leaves of any of the under- 

 mentioned species. Make with it the same tests as in the previous experiment. 



Almost any green leaf may be used, but the following are suggested : Snowdrop 

 {Galanthus nivalis), Dock {Rumex ohtusifolius), Goutweed {Aegopodium Podagraria\ 

 Dandelion ( Taraxacum officinale), Violet ( Viola odorata), Eibwort Plantain {Plantago 

 lanceolata), Elder {Samhucus nigra). 



The most important flavone pigments are apigenin, chrysin and 

 luteolin. 



Apigenin has not yet been found to be widely distributed. Its 

 formula is : 



HoA^/°^ 



OH 



OH 



It occurs in the Parsley {Garum Petroselinum) (Perkin, 12) and in 

 the flowers of the ivory-white variety of Snapdragon (Antirrhinum 

 majus) (Wheldale and Bassett, 25). 



