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 their grouping is based, may be illus- 

 trated by the following formulas; 



H 2 C CH 2 

 H 2 C CH 2 



H 



Pyrrolidine, C4HN 



H 



HC ; CH 



I / II 



HC CH 



V 



N 



Pyrridine, CsHgN 



H 2 



A 



H 2 C CH 2 



H 2 C CH 2 



Y 



J, 



Piperidine, CsHnN 



H 2 C- 



H 



-C CH 2 



NH CH 2 



or 



H 2 C 



H 2 



Tropane, 



