v] CONSTITUTION OF ANTHOCYANINS 73 



with alcohol. For the exact sequence of operations, the original paper 

 should be consulted. The nitrate from the precipitates contained 

 much of the colourless isomer. The pigment was also extracted by 

 another method in which the use of sodium chloride or nitrate was 

 eliminated. This is necessary if one wishes to obtain the naturally- 

 occurring cyanin salt, for if the method first described is employed 

 the sodium replaces the potassium originally present. In the second 

 method, the flower powder is mixed with sand, and extracted with dilute 

 alcohol (80 vols. water : 20 vols. of 96 % alcohol). It is then filtered 

 and precipitated with alcohol (3 vols. of filtrate : 5 vols. 96 % alcohol), 

 and the precipitate separated by a centrifuge. All the operations should 

 be carried out as rapidly as possible in order to avoid isonieric change. 

 The crude pigment was again purified by reprecipitation. It was 

 found that the product obtained by the first method contained sodium 

 nitrate as impurity. This was removed by extracting with 75 % 

 alcohol, in which the impurity is soluble, though not the pigment. The 

 product was, however, still further purified by precipitation, and in 

 the end contained both sodium and potassium, the former as a result of . 

 the use of sodium nitrate. The product obtained by the second method 

 (i.e. when the use of sodium salts for protection against isomerisation 

 was avoided), after purification, contained no sodium. 



By dialysis of the cyanin salt in a 20 % sodium chloride solution, 

 dark blue crystals were obtained. These Willstatter regards as an 

 addition product of the cyanin salt with sodium chloride. 



With regard to properties, the blue cyanin salt is insoluble in alcohol, 

 but soluble in water ; a concentrated water solution shows loss of colour 

 only after a day or two, but a dilute solution decolorises in an hour or 

 so. The isomerisation, as already mentioned, is best prevented by 

 sodium chloride or nitrate, but potassium nitrate or chloride has 

 little or no effect. The pure blue product shows practically no change 

 in colour on addition of a little sodium hydroxide solution, but a solution 

 of pigment which has stood becomes blue-green, or green-blue, on 

 account of the presence of the colourless modification. 



The next operation was the preparation of a crystalline salt of 

 cyanin with hydrochloric acid. The cyanin alkali salt, obtained by 

 the methods described, is dissolved in 20 % hydrochloric acid. From 

 this solution, some accompanying carbohydrates (pentosans), which are 

 present as impurity, are precipitated by addition of absolute alcohol. 

 After filtration, the pigment chloride is precipitated by ether. The 

 crude product is then taken up in absolute alcohol, which frees it from 



