66 THE ISOLATION AND [CH. 



In an alkali melt of the alcohol-soluble pigment, pyrocatechin was 

 detected as one of the products of decomposition. 



Grafe (222), 1911. The flower- pigment of Pelargonium. 



Molisch (104) had already shown that when Pelargonium petals 

 are mounted in glacial acetic acid on a slide, and covered with a cover- 

 slip, very fine crystals are formed both in the cells and in the solution 

 on the slide. After several preliminary trials had been made, the 

 following was considered by Grafe to be the best method for dealing 

 with material on a large scale. The juice is squeezed out of the petals 

 by means of a press ; the dry residue is treated with glacial acetic acid 

 for several days, and then filtered off. Both juice and filtrate are shaken 

 up with ether, and the yellowish ethereal layer separated. Glacial 

 acetic acid is added to the juice, and it is mixed with the filtrate, and 

 the mixture again filtered. The filtrate is then dialysed, and this 

 process separates the anthocyanin into two components ; the dialysate 

 is deep yellow-red in colour, and deposits groups of crystals on evapora- 

 tion, while the liquid within the membrane is dark red in colour, and 

 does not crystallise. The separation, however, can be made in another 

 way. By adding ether to the filtered glacial acetic extract, a brown 

 flaky precipitate is deposited. The filtrate is yellowish-red and gives 

 crystalline anthocyanin; the precipitate is readily soluble in water, 

 to which a little alcohol has been added, to a brown-violet fluid which 

 will not crystallise. If, also, to the glacial acetic extract, lead acetate 

 solution is added, a dense violet precipitate is formed, and the deep 

 red filtrate gives no further precipitate with lead acetate, neither will 

 it crystallise. The lead precipitate can be decomposed either with 

 sulphuric acid, or sulphuretted hydrogen, and the solution of pigment 

 therefrom crystallises in characteristic rosettes of needles. 



If the glacial acetic extract is dialysed, and the acid removed from 

 the dialysate by diminished pressure, a white crystalline precipitate 

 is formed, while the colour of the fluid becomes lighter. A microscopic 

 examination of the fluid shows a number of colourless crystalline plates, 

 together with a few rosettes of anthocyanin needles. 



The crystalline anthocyanin is also unstable and liable to give rise 

 to the amorphous form. 



The crystalline product was first investigated. It is soluble with 

 difficulty in absolute alcohol, but readily soluble in acetone. It 

 crystallises from acetic acid in good rosettes of crystals which are 

 very hygroscopic. If warmed, they give rise to the colourless crystalline 



