68 THE BOTANICAL MAGAZINE. [Vol. xxxi, No. ses. 



formed. The chromogen substance, however, is far more stable 

 than anthocyanin ; the mixture of the extract and hydrogen 

 peroxide which has been kept for more than twenty four hours 

 gives just as deep an anthocyanin colour as does a freshly 

 prepared extract when it is reduced. 



A solution of potassium permanganate also decolourizes 

 the anthocyanin solution. To the alcoblic extract of the 

 potato flower which is reduced in the manner already described, 

 a weak solution (V 50 mol.) is added drop by drop from the 

 biuret up to the point where the last drop completely decolou- 

 rizes the reduced extract. 



The aqueous extract of anthocyanin from certain flowers 

 and leaves keeps its colour for weeks without any serious 

 change if it is thoroughly boiled in order to destroy the 

 oxidising enzymes contained. The extract loses its colour 

 rapidly if the enzyme activity is not checked. Stability of dif- 

 ferent anthocyanins, however, is by no means the same ; some 

 keep the colour better than others. For example, the aqueous 

 extract from Celosia cristata is much more stable than that 

 of Pharbitis, Perilla, Chrysanthemum, Commelina and others. 



The mode of action of plant juice and hydrogen peroxide is 

 analogous. The mixture loses its colour gradually and finally 

 becomes a colourless one. The time required for dicolouri- 

 zation is inversely proportional to the concentration of the 

 oxidising substance within a certain limitation. The weaker 

 the power of oxidation in the mixture, the longer time is 

 required. This can be utilised for the estimation of the relative 

 strength of the oxidising power of the plant juice or the dried 

 powder somewhat in the following manner. Two sets of 

 parallel series of the anthocyanin solution is prepared. In one 

 of the series, a different amount of hydrogen peroxide of known 

 concentration is added, and in the other series, a different 

 amount of the plant juice is added. They are allowed to 

 stand from two to four hours in a constant temperature. At 

 the end of the period, a drop of hydrochloric acid is added to 

 each mixture of both series and the intensity of colour is com- 

 pared. In the mixture in which the anthocyanin is completely 



