248 AMIDIC ACIDS. 



The precipitate obtained as dextrin (cf §§ 76, 198, 199) must be 

 tested for nitrogen, and if much is found, experiments must be 

 made to ascertain whether any one of the following substances 

 is present. It may sometimes be approximately estimated, 

 if found, by mixing the aqueous solution with alcohol till 

 it contains abont 50 to 60 per cent, filtering, evaporating the 

 filtrate to a syrupy consistence, and now precipitating with 5 to 

 6 volumes of absolute alcohol From the amount of nitrogen in the 

 precipitate the quantity of amidic acid present may be calculated. 



Cathartic Acid occurs in senna, in the bark of Ehamnus frangiila, 

 and probably also in rhubarb.^ It is a glucoside, yielding by its 

 decomposition sparingly soluble caiAar-fo^gm'o . affoi and 34 •! per 

 cent of glucose. According to Kubly, cathartic acid' contains 

 1-48 to 1'51 per cent, of nitrogen, cathartogenic acid 2"46 per 

 cent. The latter is easily produced by heating an aqueous solu- 

 tion of cathartic acid with access of air; in fact, that substance 

 decomposes with great facility in the presence of bases and air. 

 In senna and rhubarb it is contained chiefly in combination with 

 bases (the alcohol precipitate containing 4 to 5 per cent, of aA) ; 

 but in Rhamnus frangula it appears to occur, partly at least, in 

 the free state. It is a strong purgative. 



Husson^ estimates the quality of a rhubarb by ascertaining 

 the amount of iodine an infusion is capable of absorbing ; but 

 Greenish* has shown that this method does not yield reliable 

 results. 



Sclerotic Add^ is a constituent of ergot, and contains about 4"2 

 percent, of nitrogen, but no sulphur ; its activity is not destroyed 

 by acids, etc., if in contact with them for a short period only. In 

 solubility -it resembles cathartic acid. Its actaon, when injected 

 subcutaneously into frogs and other animals, is tliatof a powerful 



' Compare Kubly, tJeber das wirksame Frincip und einige andere Best, 

 di Sennesblatter,' Diss. Dorpat, 1865, and Pharm. Zeitschr. f. RussUnd, it. 

 429, 405. On Bhamnus frangala, see also Fharm. Zeitsclir. f. Bussland, v. 160, 

 1866, On rhubarb, tbid. vi. 608, 1867 ; xvii, 65, 97, 1878 (Pharm. Joum. and 

 Trans. [3], ix. 813, 938, 1879). 



° Probably also sulphur ; cathartic acid from Bhamntu frangula bark con- 

 tains less nitrogeni 



s Union Pharm. 99, 1876 (Year-book Pharm. 344, 1*75). 



■* Pharm. Journ. and Trans. [3], ix. 818. 



* Compare Dragendorff and Podwissotzki, Archiv !. exper. Patholog. tind 

 Pharm. 153, 1876 ; Siti-Ber. d. Dorpater Naturf. Gies. 109, 392, 1877 (Pharm. 

 Journ. and Trans. [3J, vi. 1001). 



