132 liESINS, BITTEE PEINCIPLES, ETC. 



Chriiso])hanic acid, 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 (1 cc. of 86 per 

 cent, alcohol dissolves 0-00017 gram at 20° ; 1 cc. glacial acetic 

 acid dissolves O'OOOIG gram). 



Chrysophanic acid is sparingly soluble in petroleum sjDirit, 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 dichroic. 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 chrysoiDhanic 

 acid and allied substances microscopically, but it is preferable tO' 

 employ baryta- or lime-water, as with these bases comjDounds are 

 formed Avhich 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 2.50°, 

 and crystallizes in needles from glacial acetic acid. 



Erijthroretin 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.^ 



CJmjsaroh'm occurs in Goa powder ;^ it is soluble in boiling 

 l)enzene, and forms a yellow solution with cone, sulphuric acid 

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

 but with concentrated it yields a yellow solution with a green 

 fluorescence. On shaking tins liquid Avith air for some time it 

 turns red, and then deposits chrysophanic acid after acidulation. 



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

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



^ Comj)are Keussler, 'Unters, d. chrysophansiiureai't. Snbst. der Sennes- 

 blätter und der Frangul insäur e,' Diss. Dorpat, 1879, and Pharm. Zeitschr. f. 

 Eussland, 257 et seq., 1878. See also Kubly, 'Ueber das wirksame Princii) 

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

 Zeitsehr. f. Russland, 429 et ueq., 1866 (Amer. Journ. Pharm, xxxvi. 374). 



- Compare Kubly, l'harm. Zeitschr. f. Kussland, vi. 6C3, 1867. 



•' Compare Liebermann und Seidler, Per. d. d. ehem. Ges. xi. 1603 (Journ. 

 Chem. Soc. xxxvi. 326). 



