1013] on The Spectroscope in Organic Chemistry 711 



same, or very similar, it is probal)le that the substances are closely 

 related. If the composition is the same and the spectra are the 

 same, the substances are almost certainly optical isomers. Of bodies 

 related in this way we have already had an example in papaverine, 

 canadine, and tetra-hydro-berberine. 



Amongst the rare alkaloids of opium are two, to which the names 

 of laudanin and laudanosin respectively have been given. They have 

 nearly, but not quite, the same composition, laudanosin containing 

 one atom of carbon and two atoms of hydrogen more than laudanin ; 

 in other words, it is a homologue of laudanin. Substances so related, 

 hardly differ in their spectra, the replacement of one atom of 

 hydrogen by the group of atoms CHg having very little disturbing 

 influence, as we have already seen, upon the structure of a substance 

 or upon its power of absorbing light. The spectra of laudanin and 

 laudanosin being practically the same, it was inferred that they 

 possessed the same structure and were probably homologous, before 

 the fact had been ascertained by the usual chemical examination. 



I must here advert again for a moment to Stokes work on 

 absorption spectra. I mentioned at the outset that he had been 

 a1)le to distinguish all the alkaloids he examined from one another 

 by means of their absorption bands, except morphine and codeine. 

 At that time the relation of these alkaloids to one another was 

 unknown. We now know that they are homologues, and in that 

 fact have the explanation of Stokes' failure to distinguish them by 

 their absorption bands, and at the same time a striking testimony to 

 the accuracy of his observations. 



The examination of the spectra of laudanin and laudanosin not 

 only revealed the fact that the two substances are homologues, but 

 gave a clear indication as to the group of alkaloids to which they are 

 most closely allied. "When the spectra were compared with those 

 of other alkaloids, they were found to resemble the spectra of cory- 

 daline and the related alkaloids so closely as to leave very little 

 room for doubt that they are built on the same plan as these 

 alkaloids. At the time that this conclusion was arrived at, practic- 

 ally nothing was known as to the chemical structure of laudanin 

 and laudanosin, but the inference as to their close association with 

 corydaline was subsequently fully justified by chemical investigation. 



Apart from their structure there is another point of view from 

 which the study of the spectra of the alkaloids is of interest and im- 

 portance. These substances generally have very characteristic spectra 

 by means of which they can be distinguished with certainty from one 

 another, except when they are homologous or otherwise very closely 

 related. The spectroscopic method may, therefore, be used with 

 great advantage in examinations for the presence of alkaloids to con- 

 firm the results obtained by the usual chemical tests. The chemical 

 tests are no doubt as a rule sufficiently distinctive, but considering 

 the gravity of the circumstances under which they have frequently 

 Vol. XX. (No. 107) 8 b 



