520 
PROFESSOR W. H. HARTLEY OH THE 
as it exhibits two absorption bands lying between (1) 3320 and 2740, (2) 2418 
and 2199. 
Tetra-hydro-quinoline is a more diactinic substance than quinoline, it is charac¬ 
terised by two absorption bands—(1) between 3180 and 2750, and continuing to 
2870 ; (2) between 2700 and 2300, extending further to between 2650 and 2370. 
Substances, such as any of the natural alkaloids, which may be derived from 
di-hydroquinoline or tetra-hydroquinoline, by replacement of the hydrogens by other 
elements or radicals in such a manner as to have the nucleus of the compound 
unchanged, must be expected to exhibit absorption bands. 
Strychnine. —Strychnine appears to be a derivative of pyridine. 
Brucine. —The substance brucine is most probably a derivative of tetra-hydro¬ 
quinoline, or an addition product of quinoline of the same character, since there 
is a remarkable similarity between the curves of the two substances. 
I cannot close this paper without acknowledging indebtedness to the great skill 
and care that my assistant Mr. W. R. Barnett has bestowed on these later obser¬ 
vations. 
Conclusions. 
The conclusions to be drawn from this investigation are the following :— 
1. The absorption spectra oiler a ready and valuable means of ascertaining 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 difference in character of the various specimens 
known as aconitines may be recognised; thus the comparatively harmless base known 
as foreign aconitine may be distinguished from those of great physiological activity 
by its transmission of a continuous spectrum, while the three active specimens of 
aconitine are distinguished from one another by their characteristic absorption curves. 
That each of the three active aconitine bases are substances with a different consti¬ 
tution 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 directly estimated in a mixture of 
the two bodies. 
Drugs of such potency as aconitine, morphine, quinine, strychnine, &c., which 
ought to be prescribed only when of absolute purity, should be submitted to 
spectroscopic examination, so that their exact nature and degree of purity may be 
guaranteed. 
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, or of an acid radical for hydroxyl, the curve is not altered in character, 
but may vary in length when equal weights are examined. 
