Miss Wheldale, On the nature of anthocyanin. 139 



The reagents* employed were as follows: — 



(1) Strong bases, such as solutions of caustic potash or soda 

 and of ammonia. 



(2) Lime water. A blue, brown or red colour or precipitate 

 shows tannins. 



(3) Strong acids, such as sulphuric, hydrochloric and nitric 

 acids. The reactions of Brissemoret^^ are interesting in this 

 connection though they have not been employed to any great 

 extent. 



(4) Iron salts. Ferric chloride solution was used and also 

 a solution of ferrous sulphate, in which some oxidation to the 

 ferric salt has taken place. A blue-black or dull green colouration 

 shows tannins. 



(5) Precipitation by basic lead acetate which precipitates 

 most tannins and glucosides. 



(6) Potassium ferricyanide solution and ammonia. A reddish- 

 brown colouration changing to brown shows tannins. 



(7) Uranium acetate solution. A brown precipitate or 

 reddish-brown or brown colour shows tannins. 



(8) Ammonium molybdate solution, both alone and with the 

 addition of a saturated solution of ammonium chloride. According 

 to Gardiner"!* alkaline molybdate gives a red colour with tannin. 

 If excess of ammonium chloride is added, a voluminous yellow 

 precipitate is produced. Moreover by means of this reagent, 

 according to the above author, tannin may be readily separated 

 from tannic, i.e. digallic acid, for whereas the compound of tannin 

 and molybdate (?) is insoluble in ammonium chloride, that with 

 tannic acid is soluble. The reagent therefore separates the 

 glucoside tannins from tannic acid. 



As a preliminary statement it may be said that tannins, like 

 that of the oak gall, giving an intense blue-black colour with iron 

 salts and also reactions 2, 6, and 7 are rare among herbaceous 

 plants. There are however widely distributed among the latter, 

 certain colourless or slightly yellow substances, giving an iron- 

 greening reaction though they are not typically tannins, since 

 they do not as a rule give reactions 2, 6, 7, and 8. These substances 

 are characterised in addition by the bright yellow colour produced 

 when they are acted upon by strong bases and by lime-water. 

 They give the same colour also with strong mineral acids, such 

 as sulphuric and hydrochloric, and they are precipitated by basic 

 lead acetate as canary-yellow precipitates. 



These reactions are best seen when extracts of white flowers 

 are used or those of 3^ellow flowers, in which the colour is due 

 to plastid pigment only. Flowers giving these reactions are 

 arranged in the following scheme. 



* Darwin and Acton, Physiology of Plants. t (iardiuer ". 



