v] CONSTITUTION OF ANTHOCYANINS 63 



alcohol and precipitating with ether. (2) The lead precipitates are 

 heated with acetic acid, in which the lead salt- of B is soluble, whereas 

 that of A is insoluble. Heise gave to B the formula C 20 H 24 12 . By 

 heating B with dilute hydrochloric or sulphuric acid, A was formed 

 together with sugar. Hence Heise concluded that B is a glucoside. 

 The decomposition of the glucoside is represented as follows : 



C 20 H 24 12 + H 2 = C 14 H 14 7 + C 6 H 12 6 



The pigment B is described as a reddish-violet powder, soluble in 

 water, alcohol and acetic acid, insoluble in ether, benzene, chloroform 

 and carbon bisulphide. It reduces Fehling's solution : gives, a bluish- 

 green precipitate with lead acetate, and an intense red colour with acids. 



The pigment A is a dark brown powder : it is soluble in 60 % 

 alcohol to a red-brown solution, or in acid alcohol to a red solution ; 

 it is insoluble in cold water (either neutral or acid), in absolute methyl 

 or ethyl alcohols, chloroform, ether and carbon bisulphide. The re- 

 actions of A varied, but were on the whole as follows : dirty bluish-green 

 colour with ammonia, dirty green precipitate with lead acetate and a 

 black precipitate with ferric acetate. On fusion with caustic potash, 

 protocatechuic acid was identified as a product of decomposition. 



Griffiths (191), 1903. The flower-pigment of Pelargonium. 



The pigment was extracted with alcohol and the solution gave, 

 on evaporation to dryness, a crystalline substance. The analyses of 

 the results were: 



C H 



From anthocyanin 62-85 % 3-53 % 33-62 % 



Calculated for C 15 H 10 6 ... 62-93% 3-49% 33-58% 



An acetyl derivative was obtained by heating the pigment with 

 acetic anhydride and sodium acetate; it crystallised from methyl 

 alcohol in red needles melting at 125 C. If potassium acetate is added 

 to a hot alcoholic solution of the pigment, orange prisms are obtained. 

 An analysis of the potassium salt gave the following result: 



K 21-50% 



Calculated from C 15 H 8 6 K 2 : 



K 21-54% 



Grafe (197, 209), 1906, 1909. The flower- picjment of Althaea rosea. 



Preliminary experiments showed that the extraction of the petals 

 with water or dilute acid is impracticable, since so much mucilage is 



