M. Wheldale 113 



intense yellow colour with alkalies ; this reaction is readily seen when 

 parts of plants, which are free from chlorophyll, are immersed in 

 ammonia vapour. White flowers under these conditions turn canary- 

 yellow. When water extracts of glucosides of the flavones are hydrolysed 

 by boiling with an acid, the flavone separates out from the solution 

 owing to the fact that it is less soluble than it was when in the form 

 of a glucoside. The flavones themselves are yellow crystalline substances, 

 as a rule readily soluble in alcohol, sparingly soluble in ether, and almost 

 insoluble in water. Their solutions give yellow or orange precipitates 

 of lead salts with lead acetate and generally a green or brown coloration 

 with ferric salts. The colour of the flavones is due to the chromophore 

 group : 



o 



c 



II 

 o 



in conjunction with hydroxyl groups, the auxochromes, the intensity of 

 colour depending on the position of the latter (Smiles, 22). When the 

 hydroxyl groups are replaced by sugar or by acetyl or benzoyl radicals 

 a coloui'less, or practically colourless, compound is produced, since the 

 effect of the auxochromes is eliminated. 



The fact that the flowers of the ivory variety of Antirrhinum 

 become yellow in ammonia vapour suggested that the pale yellow or 

 ivory pigment might be a flavone. 



Ivory pigment was prepared from the upper lips of ivory flowers in 

 the following way (W^heldale, 32). Large quantities of material were 

 boiled with water, filtered, and poured into lead acetate solution which 

 precipitates the pigment as a canary-yellow lead salt. This was filtered 

 otf and decomposed by dilute sulphuric acid which precipitates the lead 

 as lead sulphate, the pigment being set free again in solution. After 

 filtering off the lead sulphate, the pigment in the dil ite acid solution 

 was boiled, by which means the glucoside is hydi'olysed, and on cooling, 

 the free pigment is deposited as a brownish-yellow precipitate which is 

 filtered off and dried. 



The crude pigment was then purified by extracting in a Soxhlet 

 thimble over boiling ether in which the ivory pigment is soluble and 



