74 THE ISOLATION AND [CH. 



colloidal substance and other impurities. The purified alcoholic solu- 

 tion is then acidified with strong hydrochloric acid, and concentrated in 

 a vacuum desiccator. Cyanin chloride separates out as an amorphous 

 product which is soluble in both alcohol and water to a bright red 

 solution ; the solution becomes rapidly paler, but in absolute alcohol, 

 the loss of colour is much less rapid than in the presence of water. To 

 obtain the crystalline form, the amorphous product is dissolved in 

 absolute alcohol, filtered, and mixed with a third of its volume of a 

 7 % solution of hydrochloric acid in water, and set to crystallise. The 

 crystals are deep blue rhomboidal plates with a golden lustre: in a 

 powdered form, the colour is brown-red. The chloride crystallises out 

 with three molecules of water of crystallisation, and the formula obtained 

 by elementary analysis is CagHggO^Cl . 3H 2 0. The water-free product 

 on analysis gave C 28 H 33 17 C1. The crystalline cyanin chloride is almost 

 insoluble in water, soluble with difficulty in cold alcohol, acetone and 

 chloroform; insoluble in benzene; slightly soluble in dilute hydro- 

 chloric and sulphuric acids. It is stable in acid solution : in water 

 solution it decolorises, with the formation of the isomer, especially 

 if dilute, but the colour returns on acidification. The colourless isomer 

 is also formed by warming with absolute alcohol ; such a solution then 

 gives with lead acetate a green precipitate, on account of the mixture 

 of the blue salt of the pigment with the yellow alkali salt of its isomer. 

 Pure cyanin chloride gives with calcium carbonate a violet solution; 

 with sodium hydroxide, a blue solution ; with lead acetate, a blue 

 precipitate, which gives a green lead salt on standing ; and with sodium 

 carbonate, a violet colour which eventually becomes yellow. The 

 chloride is reduced with zinc and hydrochloric acid, and also decolorised 

 with sodium bisulphite, the colour in the latter case returning on 

 addition of an acid. As a glucoside it reduces Fehling's solution. 



The glucoside cyanin is rapidly hydrolysed with 20 % hydrochloric 

 acid, cyanidin being formed which separates out as the chloride from 

 the hot solution. The combined sugar was identified as glucose. The 

 crystals, in the form of needles, of cyanidin chloride are brown-red 

 under the microscope, give a violet streak, and a brown-red powder. 

 They have no water of crystallisation, and an elementary analysis gave 

 the formula C 16 H 13 7 C1. The chloride is soluble in alcohol with a fine 

 violet-red colour ; it is also soluble with difficulty in dilute hydrochloric 

 acid. It crystallises from a mixture of alcohol and dilute hydrochloric 

 acid. It is also soluble in amyl alcohol, and when such a solution is 

 shaken with caustic soda solution, the pigment goes into the watery 



