VII] 



OXIDIZING ENZYMES 



97 



(6) Add a little lead acetate .solution. An orange precipitate of the lead salt is 

 formed. 



(c) Add a little ferric chloride solution. A green coloration is produced. 



(d) Heat some of the alcoholic solution on a water-bath, acidify with strong 

 hydrochloric acid and add zinc dust. A magenta colour is produced (see p. 106). 



Expt. 99. Preparation of crude quercetin from Onion skins (Perkin, 21). Take 

 about 50 gms. of the brown outer skins of onions and boil with 900 c.c. of water for 

 an hour. Then filter and allow the filtrate to stand for 24 hrs. A brownish -yellow 

 deposit is formed which is crude quercetin. Filter this off and dissolve in 75% 

 alcohol and allow to evaporate slowly. Quercetin will be deposited. With a solution 

 in dilute alcohol make the same tests as in the last experiment. 



Expt. 100. Preparation of a quercetin glucoside from Wallflower (Cheiranthus 

 Cheiri) flowers (Perkin and Hummel, 22). Take 20 gms. of petals of flowers of either 

 the brown or yellow variety and drop them into boiling alcohol in a flask. Filter and 

 evaporate the extract to dryness on a water-bath. Dissolve the residue in water and 

 add ether. In the case of the yellow variety the yellow plastid pigments are taken 

 up by the ether, and the quercetin glucoside partly crystallizes out from the water 

 as in Expt. 98. In the case of the brown variety both quercetin glucoside and 

 anthocyan pigment are present as well as plastid pigments. The two former go into 

 solution in the water and the glucoside in time crystallizes out. In either case the 

 glucoside can be filtered off and tested as in the previous experiment. A positive 

 result will be given in each case. 



Kaempferol occurs in the flowers of a species of Larkspur (Delphi- 

 nium consolida) (Perkin and Wilkinson, 25) and Prunus (Perkin and 

 Phipps, 24) and in the leaves or flowers of several other plants. It has 

 the formula : 



HO 



Myricetin and fisetin are two other flavones which have been found 

 in species of Sumac (Rhus) and other plants. They have respectively 

 the formulae : 



OH 



HO 



Myricetin 



OH 



o. 



