4 



The Absorption-spectra of the Alkaloids. [Dec. II,. 



1. The absorption- spectra offer a ready and valuable means of ascer- 

 taining the purity of preparations of the alkaloids, and particularly 

 of establishing their identity. 



The quantity of some of the alkaloids present in a solution may be 

 estimated by means of the absorption curves. 



The different character of the various specimens known as aconi- 

 tines may be recognised ; thus the comparatively harmless base may 

 be distinguished from those of great physiological activity by its 

 transmission of a continuous spectrum, while the three specimens of 

 physiologically active aconitines are distinguished from one another by 

 their characteristic absorption curves. 



That the three active aconitine bases are substances each with a 

 different chemical constitution, is a conclusion confirmed by optical 

 examination. 



The purity of quinine and absence of any admixture of cinchonine 

 can be readily determined by reason of the latter substance being 

 much less diactinic than the former ; but for the same reason quinine 

 cannot be estimated in presence of cinchonine. Drugs of such potency 

 as aconitine, morphine, quinine, strychnine, &c, which ought to be 

 prescribed only when of absolute purity, should have their exact 

 nature and degree of purity guaranteed by an examination of their 

 absorption-spectra. 



2. In comparing the spectra of substances of similar constitution, 

 it is observed that such as are derived from bases by the substitution 

 of an alkyl radical for hydrogen and acid radicals for hydroxyl, the 

 curve is not altered in character, but may vary in length when 

 equal weights of substances are examined. This is explained by 

 the absorption-band being dependent upon the compactness of struc- 

 ture of the carbon and nitrogen nucleus of the molecule, and because 

 equal weights are not molecular weights. Examples are afforded by 

 morphine and codeine (methyl-morphine), diacetyl-codeine, and 

 tetracetyl-morphine. 



3. Bases which contain oxidised radicals, as hydroxyl, carboxyl, or 

 methoxyl, diminish in diactinic quality in proportion to the amount of 

 oxygen they contain. Examples are papaverine, narceine, narcotine, 

 and oxynarcotine. 



The apo- derivatives are less diactinic than the parent bases in a 

 degree which indicates that the molecular weights have been nearly 

 doubled. Examples are apo-morphia and pseudaconitine. 



4. Bodies with the pyridine and quinoline nucleus exhibit absorp- 

 tion-bands extending between wave-lengths 350 and 280, those with 

 a benzene nucleus generally from 290 to 260, or rays even more 

 refrangible ; while the aconitines and opium bases, likewise strychnine, 

 give evidence of a benzene nucleus, the cinchona bases, with piperine 

 and brucine, appea - " to contain a nucleus of quinoline or pyridine. 



