REACTIONS OF ALKALOIDS 



41 



Potassium mercuriodide (Mayer's reagent), giving 

 a white precipitate. 



Potassium tri-iodide, giving a brown precipitate. 



Gold chloride, giving a yellow precipitate. 



In addition to the above general precipitants, the 

 alkaloids may be distinguished from each other by 

 means of certain distinctive colour tests. 



The general colour reagents most usually employed 

 in the case of the commoner alkaloids arq the 

 following : — 



Concentrated HNO3; concentrated HgSO^ ; and 

 concentrated HgSO^ together with a crystal of potas- 

 sium bichromate ; while Erdmann's reagent (concen- 

 trated H2SO4, containing -oi per cent, concentrated 

 HNO3), Froehde's reagent (i per cent, solution of 

 (NHJg M0O4 in concentrated HgSOJ, and Mandelin's 

 reagent (-5 per cent, solution of vanadium chloride 

 in concentrated HgSOJ afford characteristic colour 

 reactions in certain cases. 



The reactions given with certain of the commoner 

 alkaloids are tabulated herewith : — 



Special confirming tests are as follows : — 

 Morphine. — (i.) A small quantity of formaldehyde 



added to the alkaloid or one of its salts, followed by 



two or three drops of strong HgSO^ produces an intense 



purple colour. 



(ii.) Froedhe's reagent (see above) gives a violet 



colour changing to dirty green. 



