ALKALOIDS 367 



vomica be mounted in a few drops of strong sulphuric acid, 

 the presence of strychnine is indicated by a red coloration 

 of the cell-contents. This colour will change to violet on 

 placing a small crystal of potassium chromate beneath the 

 cover-glass. 



Similarly, a section of the rhizome of Aconitum Napellus, 

 when treated with a few drops of 50 per cent sulphuric acid, 

 will shown a carmine red coloration, due to the presence of 

 aconitine, in the parenchyma surrounding the vascular bundles. 

 This reaction is the more marked when the section has been 

 previously warmed in a solution of sucrose. 



These colour reactions are very numerous ; for them the 

 larger text-books and monographs must be consulted. 



Isolation. 



Most alkaloids do not occur free in the plant, but com- 

 bined with some acid in the form of a salt ; the acids most 

 commonly met with are tannic, malic, citric, succinic, and 

 oxalic, while acetic and lactic acids are rarer ; some acids 

 occur only in connection with certain alkaloids, such as 

 meconic acid with opium and quinic acid with quinine. 



In some few cases the alkaloids can be extracted from 

 their natural sources by means of organic solvents, such as 

 chloroform, carbon tetrachloride, ether, etc., but in the 

 majority of cases the alkaloid requires to be set free first by 

 the addition of an alkali, such as lime or baryta, since only 

 the free bases, and not the salts, are soluble in the above- 

 mentioned solvents. 



The material to be extracted is mixed with slaked lime 

 and carefully dried, and then extracted in a Soxhlet extractor 

 with chloroform or carbon tetrachloride ; the extract is then 

 shaken up with dilute sulphuric acid, whereby the sulphate is 

 formed ; the acid layer containing the salt in solution is then 

 run off and evaporated, when the alkaloid salt crystallizes out 

 and can be further purified by recrystallization. 



Example. — Preparation of quinine from cinchona bark. 

 Twenty grams of quicklime are stirred up with 200 c.c. of 

 water and then thoroughly mixed in a mortar with 100 grams 



