270 NITROGEN BASES 



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

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

 occur only in connexion 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 

 of cinchona bark which have been ground up in a coffee mill. 

 The resulting mixture is then dried over a water bath, care 

 being taken to prevent the formation of lumps. The dried 

 substance is then extracted in a Soxhlet apparatus with 

 chloroform. The extract is then shaken up with 25 c.c. of 

 dilute sulphuric acid, the chloroform layer being run off from 

 below ; it is then shaken up with water several times and the 

 water and acid extracts are mixed together and neutralized 

 with ammonia. On evaporating the solution, quinine sulphate 

 crystallizes out ; the amount obtained rarely exceeds I -2 

 grams in weight. 



A rapid way of testing a piece of bark for quinine 

 consists in heating it in a dry test tube. If there is any 

 quinine present, the bark will s^ive off a carmine-coloured 

 vapour. 



