444 CHEMICAL DISCOVEEY AND INVENTION 



shade. On the other hand, the action of alkaline solutions is to 

 produce from any of them a green colour. These colouring 

 matters appear to be formed by oxidation from colourless sub- 

 stances resident in the substance of the petal. If a red or purple 

 stock, for example, is immersed in strong spirit of wine the colour 

 is dissolved out rapidly and the petals become colourless. If the 

 decolourised petals are then placed in water at room temperature 

 they begin almost at once to regain their colour, and in a quarter 

 of an hour each petal is found to have recovered its original 

 colour, and in the same parts of the petal which exhibited the 

 colour, so that a white striped purple variety reproduces faith- 

 fully the purple and white pattern of the original. 



It appears probable that there is a genetic connection 

 between the yellow pigments present in many flowers and the 

 red and blue colouring matters. It is stated by Dr. Everest 

 (Proc. Royal Soc., 1914, p. 326), that under the influence of 

 reducing agents (magnesium and hydrochloric acid preferably), 

 the former yield red substances which answer to the tests and 

 characters of the anthocyanins. Eesearch on this fascinating 

 subject appears to be proceeding in the right direction, and as 

 the constitution of the yellow substance is almost agreed upon 

 by the chemists who have been occupied with the question the 

 constitution of the anthocyanins will probably soon become 

 clear. This does not mean that chemists or botanists are likely 

 to be able to tell us how the plants produce their decorative 

 pigments ; that is another question which will probably take a 

 long time to solve. 



An investigation by Professor Willstatter of two yellow sub- 

 stances which occur together with chlorophyll in green leaves 

 has led to some curious results. One of these, identical with the 

 yellow colouring matter of the carrot and in reference to that 

 fact named carrotene, is a hydrocarbon with the molecular for- 

 mula C 40 H 56 . It crystallises in copper coloured leaflets which 

 transmit a red light, but it absorbs oxygen readily and is con- 

 verted into a colourless substance. 



Xanthophyllj which accompanies chlorophyll in the alcoholic 

 extract of leaves, is similar to carrotene in appearance, but is 

 yellow. It has the formula C 40 H 56 2 . It behaves neither as an 

 acid, an alcohol, nor ketone. It absorbs oxygen readily, and is 

 thereby converted into a colourless compound C 40 H 56 18 . 



The story of all these natural dyes, with which earth's garment 



