ABSORPTION SPECTRA OF THE ALKALOIDS. 
519 
genised addition-product of methyl-pyridine. A pyridine nucleus hydrogenised would 
yield no absorption band and would be very diactinic. 
In tropic acid we have a substance capable of manifesting the benzene nucleus 
by giving a banded spectrum; if however it be modified by hyclrogenising, this pro¬ 
perty disappears. As atropine not only exhibits no absorption band, and is, moreover, 
a remarkably diactinic substance, it is highly probable that both the pyridine and 
benzene residues are hydrogenised. (Compare hyoscyamine and piperine.) 
Hyoscyamine is isomeric with atropine; on treatment with baryta water it yields 
tropine and tropic acid. Like atropine it is remarkably diactinic, layers of solutions 
20 millims. in thickness, which contained one part of the substance in 200 of alcohol, 
transmitted all rays in the case of atropine to wave-length 2700, and of hyoscya¬ 
mine to wave-length 2740, 
Caffeine, or methyltheobromine, C 8 H 10 N/AH-HoO, has been shown to have the 
constitution of a tri-methyl-xanthine. According to Emil Fischer its structure is 
represented thus :— 
ch 3 n-ch 
I I 
CO CN.CHo 
I I > C0 
ch 3 n-c=n 
There are no reasons for believing that such a body would yield an absorption band, 
indeed there is much evidence to lead one to think that it would not. We may 
therefore say that its supposed constitution is in accordance with its absorption 
spectrum. 
p y ridine, quinoline and derivatives. 
The absorption band characteristic of pyridine is strongest between wave-lengths 
2700 and 2300, with diminished intensity it extends from 2570 to 2400. It appears 
highly probable that this substance enters into the constitution of morphia and some 
other of the opium bases. 
As was predicted piperidine shows no absorption band, but still, like the terpenes, 
it possesses considerable absorptive power, which is exerted on the more refrangible 
rays, extending continuously to wave-length 2420. 
The absorption spectra of two specimens of quinoline yield curves which are pre¬ 
cisely similar. The band of absorption is strongest between wave-lengths 3170 and 
2600, continuing with diminished intensity it lies between 2980 and 2830. There is 
in addition a remarkable narrow band of absorption which is very well defined, it lies 
between 3085 and 3039, and continues with but slightly diminished intensity between 
3078 and 3039. 
Quinoline hydrochloride yields a spectrum differing from that of the base inasmuch 
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