268 NITROGEN BASES 



their constitution is not entirely known ; these include amongst 

 others ergotinine from ergot, colchicine from Colchicum, taxine 

 from Taxus baccata, aconitine from Aconitum Napellus, del- 

 phinine from Delphinium, etc. 



GENERAL PROPERTIES OF ALKALOIDS. 



The alkaloids are, as a rule, composed of the four elements, 

 carbon, hydrogen, nitrogen, and oxygen, but a few are known, 

 such as coniine, nicotine, and one or two little-known ones, 

 such as hymenodictine and conessine (from bark of Wrightia 

 antidysenterica\ which contain no oxygen. 



There are a few alkaloids which are liquid, e.g., coniine, 

 nicotine, pelletierine, sparteine, etc., but by far the greater 

 number are colourless crystalline solids. They are, as a rule, 

 insoluble in water, but dissolve in neutral organic solvents, 

 such as ether, amyl alcohol, chloroform, carbon tetrachloride, 

 etc., whereas their salts have just the opposite solubilities. 



They are mostly free from smell, but coniine, nicotine, 

 and sparteine have strong odours. 



Most of them have a bitter taste and are possessed of 

 marked physiological or toxic properties. 



They are all bases, and accordingly have an alkaline 

 reaction in solution, though it must be borne in mind that 

 aqueous solutions of the salts usually have a strongly acid 

 reaction due to hydro ly tic dissociation. 



The majority of alkaloids are optically active, rotating the 

 plane of polarized light to the left, though a few, such as 

 coniine, laudanosine, pelletierine and pilocarpine, are dextro- 

 rotatory. 



GENERAL REACTIONS OF ALKALOIDS. 



The alkaloids are precipitated from solution by a large 

 number of different reagents with formation of amorphous or 

 sometimes crystalline precipitates. 



The commonest of these reagents are the following : 

 I. A solution of iodine in potassium 

 iodide, sometimes known as 

 potassium ter-iodide, gives a 

 chocolate-brown precipitate. 



