154 



CHEMISTRY OF PLANT LIFE 



The alkaloids are precipitated out of their solutions by various 

 solutions of chemical compounds, known as the " alkaloidal 

 reagents": iodine dissolved in potassium iodide solution gives a 

 chocolate-brown precipitate; tannic acid, phosphotungstic acid, 

 phosphomolybdic acid, and mercuric iodide solutions give color- 

 less, amorphous precipitates; while gold chloride and platinic 

 chloride solutions give crystalline precipitates, many of which have 

 sharp melting points and can be used for the identification of 

 individual alkaloids. There are a great many specific color 

 reactions for individual alkaloids, which are important to toxi- 

 cologists and pharmacists, but which it would not be desirable to 

 consider in detail here. 



The alkaloids are conveniently divided into groups, according 

 to the characteristic closed-ring arrangements which they contain. 

 The several closed-ring arrangements which are found in common 

 alkaloids, and upon which x their grouping is based, may be illus- 

 trated by the following formulas; 



Hs 



-CH 2 



H 2 C CH 2 



Y 



H 



Pyrrolidine, C4H 9 N 



H 



C 



HC CH 



1 II 

 HC CH 



v 



N 



Pyrridine, CsHsN 



H 2 



H 2 C CH 2 



I I 



TT f~\ f~~*TT 



1 2 1~/ 1^1 2 



Y 



H 



Piperidine, CsHuN 



CH 2 



H 2 C 



CH 2 



or 



CH 2 



Tropane, CrHijN 



