v] CONSTITUTION OF ANTHOCYANINS 71 



The results of combustion of the pure anthocyanin were: 



C H O 



Eed anthocyanin : from rose dore 51-93 % 5-02 % 43-05 % 



bronze ... 51-37% 5-05% 43-58% 



^9.12 / 4-Q7 / 42-Q1 / 



,, ,, ,, ,, ... Ol il / Q Vi /Q tA Ul /Q 



Magenta magenta 50-26 % 4-89 % 44-85 % 



ivory tinged 



with magenta 50-68% 5-54% 43-78% 



from crimson ... 50-56% 4-90% 44-54% 



Attempts were made to determine the molecular weight by depression 

 of freezing point, using phenol as a solvent, but the results, though 

 consistent for a series of experiments, were obviously far too low. ' 

 Acetic acid, and various other solvents, did not dissolve enough of 

 the pigment to give measurable depressions. Attempts to determine 

 the molecular weight by elevation of the boiling point in absolute 

 alcohol gave mean values of 572 for the red, and 717 for the magenta. 

 The elevation of the boiling point was so slight that the error in the 

 value obtained may be very considerable. 



The combustion results give, as simplest formulae, C 15 H 18 10 for the 

 magenta, and C 8 H 9 5 for the red. The boiling point determination 

 of the molecular weight would appear to indicate that the molecule 

 is 2 (C 15 H 18 10 ), i.e. C 30 H 36 0. 20 , which has a molecular weight of 716 

 for the magenta, and 3 (C 8 H 9 5 ), i.e. C 24 H 27 15 , which has a molecular 

 weight of 555 for the red. 



An attempt was made to estimate the number of hydroxyl groups 

 present in the anthocyanin molecule by means of ZerewitinofFs modifi- 

 cation of Hibbert & Sudborough's method. This consists in dissolving 

 the substance in thoroughly dried pyridine, treating it in a suitable 

 apparatus with a considerable excess of methyl magnesium iodide, and 

 collecting the gas evolved. Each hydroxyl group causes the evolution 

 of a molecule of methane. It should be noticed that 'hydroxyl groups,' 

 as determined by this method, include those forming part of the carboxyl 

 groups, and also such ketone groups as can give rise to hydroxyl by 

 tautomeric change. The values obtained indicate that the red antho- 

 cyanin, taking the formula as C^H^Ojg, contains twelve hydroxyl groups 

 as defined above, while the magenta, taking the formula as C 30 H 36 20 , 

 contains fifteen hydroxyl groups. 



