68 THE ISOLATION AND [CH. 



sulphate formed as barium sulphate. Both methods gave numbers 

 indicating the presence of two aldehyde groups. In the opinion of 

 Grafe, it is the aldehyde groups which determine the colour in the 

 anthocyanin. An alkali melt was made of the pigment, and pyro- 

 catechin was identified as one of the products of decomposition. The 

 formula for anthocyanin is then represented by Grafe as 



C 13 H 19 3 (OH) 2 (COOH) 3 (COH) 2 . 



An analysis was also made of the colourless crystalline products 

 which are formed when acetic acid is driven off from the acetic acid 

 solution of anthocyanin. The colourless crystals are soluble in water, 

 alcohol and ether. The substance was identified on analysis, etc., 

 as protocatechuic acid. Some doubt is expressed by Grafe as to whether 

 this substance is a decomposition product, or whether it is present as 

 impurity. 



The amorphous anthocyanin was next investigated. This product 

 forms the principal part of the total pigment extracted. After drying, 

 it is soluble with difficulty in water, but readily soluble in dilute alcohol. 

 With acids it gives a less bright colour than the crystalline form : with 

 alkalies, a greenish-brown colour, while sodium bisulphite removes the 

 colour. 



The analyses gave: 



C H O 



From anthocyanin ...... 43-78% 6-22% 50-0% 



Calculated from C^H^Oso ... 44-17% 6-75% 49-08% 



The molecular weight was determined in phenol, and found to be 

 663 as compared with 652 calculated for C^H^ao. 



This latter product was found to be a glucoside, and dextrose was 

 identified as one of the products of hydrolysis with acid. Grafe suggests 

 that the relationship between the two pigments may be represented 

 thus: 



(amorphous) 



H 2 == C G H 12 6 



- 4H 2 + 2 = C 18 H 26 13 



(crystalline) 



He is also of the opinion that the amorphous form arises by changes 

 induced in the crystalline, rather than vice versa, since the crystalline 

 is never produced from the amorphous, but the latter may arise from 

 the former. 



