26o NITROGEN BASES 



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 hydrolytic 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 : — 



1. A solution of iodine in potassium 



iodide, sometimes known as 

 potassium ter-iodide, gives a 

 chocolate-brown precipitate. 



2. Mercuric iodide in potassium ] all of which 



iodide, |^ give colourless 



3. Tannic acid, amorphous precipi- 



4. Phosphotungstic acid, j tates. 



which give crystalline 



precipitates often 

 having characteristic 

 melting points. 

 The alkaloids are, however, not the only substances which 

 are thrown out of solution by these reagents, since most 

 nitrogen bases behave in a similar way, and the formation of 

 a precipitate is therefore not conclusive proof of the presence 



5. Auric chloride, 



6. Platinic chloride (see p. 266), 



