130 Professor Julius Wilhelm Brilhl [May 26, 



Several simple molecules of this kind may be combined into one 

 crystallised particle of the spectrochemically normal diamond. 



§ 15. Thanks to the explanation of the optical behaviour of 

 benzene, with the resultant discoveries, it all at once became possible 

 to understand the causes of the spectro-chemical abnormality of whole 

 classes of bodies, such as the defines, diolefines, terpenes, aromatic 

 compounds, etc., and light was cast on the chemical constitution of 

 whole classes of bodies. 



At the same time, however, it at once became apparent why both 

 Landolt and Grladstone had succeeded in observing complete optical 

 normality in very numerous substances of the most various types — 

 alcohols, acids, ethers, hydrocarbons, etc. And now it was under- 

 stood why in such bodies the molecular refraction is determined 

 solely by the component elements, while the different grouping of 

 the atoms, i.e. the isomerism, remains without any appreciable optical 

 influence. 



All the bodies of this kind proved to be either paraffins, i.e. satu- 

 rated hydrocarbons, or simple derivatives of the same. But the 

 paraffins, as we now know, are always optically normal, because they 

 contain no double carbon bonds. For this reason all such simple 

 derivatives of the paraffins must also be normal. Their molecular 

 refraction will thus always correspond to the elements of which they 

 are composed, however the atoms may be grouped, i.e. chemical 

 isomerism is here also without influence. 



§ 16. For the same reason, however, all cycloid (ring-shaped) 

 closed formations, if they contain no double carbon bonds, must be 

 optically normal, for those bodies also may be conceived as origina- 

 ting in the simple replacement of hydrogen by paraffin fragments, 

 and may therefore be regarded as combined paraffins. 



Thus we can imagine the hexamethylene already mentioned not 

 only as formed from hexane by removal of two hydrogen atoms from 

 the ends, but also as arising from ethane and butane, i.e. from two 

 paraffins, by the removal of four hydrogen atoms and welding 

 together of the remains : — 



C C" 



/H / \ 



HjC HCHj H^C CHj 



Butane I I Ethane 



H, Ho 



Hexamethylene 



As a combined paraffin, hexamethylene must be normal, as is also 

 confirmed by experiment, and here we see again, as in the case of the 



