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 approximatehj estimated, 

 if found, by mixing the aqueous solution with alcohol till 

 it contains about 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 f rangula, 

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

 decomposition sparingly soluble cathartogenic acid and 34*1 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 ash) ; 

 but in Ehamnus 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 Acid^ is a constituent of ergot, and contains about 4*2 

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

 by acids, etc., if in contact with them for a short i^eriod only. In 

 solubility it resembles cathartic acid. Its action, when injected 

 subcutaneously into frogs and other animals, is that of a powerful 



^ Compare Kubly, ' Ueber das wirksame Princip und einige andere Best, 

 d. Sennesblätter,' Diss. Dorpat, 1865, and Pharm. Zeitschr. f. Pussland, iv. 

 429, 465. On Ehamnus frangiila, see also Pharm. Zeitschr. f. Eussland, v. 160, 

 1866. On rhubarb, ibid. vi. 603, 1867 ; xvii. 65, 97, 1878 (Pharm. Journ. and 

 Trans. [3], ix. 813, 933, 1879). 



- Probably also sulphur ; cathartic acid from Ehamnus frangula bark con- 

 tains less nitrogen. 



3 Union Pharm. 99, 1875 (Year-book Pharm. 344, 1875). 



* Pharm. Journ. and Trans. [3], ix. 813. 



' Compare Dragendorff and Podwissotzki, Archiv f. exper. Patholog. und 

 Pharm. 153, 1876 ; SitzBer. d. Dorpater Naturf. Ges. 109, 392, 1877 (Pharm. 

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



