132 BESINS, BITTER PRINCIPLES, ETC. 



Chfrysophank add, as obtained' from rhubarb, senna/ etc., is 

 almost insoluble in water, but if in combination with a base it 

 can be extracted from aqueous solution by adding a strong acid 

 and shaking with ether. The solubility in alcohol and acetic acid 

 varies directly with the strength of the solvent (I cc. of 86 per 

 cent, alcohol dissolves 00017 gram at 20°; 1 cc. glacial acetic 

 acid dissolves 0'00046 gram). 



Chrysophanic acid is sparingly soluble in petroleiim spirit, but 

 is dissolved by benzene and chloroform, especially when warm. 

 It can be sublimed in flat rhombic prisms, which melt at 162°, 

 are yellow in colour, and strongly dlchroic. It is easily dissolved 

 by alkaline liquids, both aqueous and alcoholic, with production of 

 a fine red colour, for particulars of the spectrum of which refer- 

 ence must be made to Keussler's dissertation. This colouration 

 in contact with alkali serves as a means of detecting chrysophanic 

 acid and allied substances microscopically, but it is preferable to 

 employ baryta- or Ume-water, as with these bases compounds are 

 formed which are insoluble in water. 



Emodin agrees with chrysophanic acid in most of its properties, 

 but may be distinguished by its insolubility in benzene, and 

 greater solubility in ether and alcohol. It melts at 245° to 250°, 

 and crystallizes in needles from glacial acetic acid. 



Erythroretin and Phceoretin may also be obtained from rhubarb ; 

 they are both sparingly soluble in ether, freely in- alcohol ; the 

 former is coloured purple-red by alkalies, the latter reddish- 

 brown. ^ 



Chrysarohin occurs in Goa powder;* it is soluble in boiling 

 benzene, and forms a yellow solution with cone, sulphuric acid 

 (chrysophanic acid, red). It in not dissolved by dilute potash, 

 but with concentrated it yields a yellow solution with a green 

 fluorescence. On shaking this liquid with air for some time it 

 turns red, and then deposits chrysophanic acid after acidulation. 



65, 97, 1878 (Phamj. Joum. and Trans. [3]. viii. 826), and the continuation of 

 the paper by Greenish, Pharm. Joum. and Trans. [3], ix. 933. 



' Compare Keussler, ' Unters. d. , chrysophatiaaureart^ Snbst. der Seines- 

 blatter und. der Erangnlinsaure,' Diss. Dorpat, 1879, and Pharm. Zeitsohr. f. 

 E,us.sland, 25.7 et aeq., 1878. See also Kubly, ' Ueber das, wirksame Prinoip 

 und einige andere Best. d. Serinesblatter,' Diss. Dorpat, 1865, and Pharm. 

 Zeitschr. f. Bussland, 429 et seq., 1866 (Amer. Joum. Fharm. xzxvi. 874). 



^ Compare Kubly, Pharm. Zeitsohr. f. Eussland, vi. 60S; 1867. 



' Compare Liebermann und Peidler, Ber. d. d. chem. Ges. ii. 1603 (Joum 

 Chem. Soc. xxxvi. 326). 



