1905.] 



on the Development of Spectr o- Chemistry . 



129 



for benzene is really the only graphic representation of its structure 

 in a single plane which is confirmed by chemical optics. 



Thus it can be at once determined by optical methods whether a 

 given body belongs to the paraffinoid, olefinoid, or cycloid products ; 

 whether these products contain double bonds or not ; and if so, how 

 many. 



Now, too, we can imagine why the diamond, i.e. pure crystallised 

 carbon, is, as akeady mentioned, optically normal. We obtain an 

 idea of the mineral's chemical constitution, and of the way in which 

 the atoms of carbon are perhaps combined in the sparkling gem. 



For the reasons already stated, the diamond cannot possibly con- 

 tain any double bonds ; a combination, say, in the form 



^^^ 



with one atom of carbon at each of the six corners, and with each 

 atom connected with its neighbour by a double bond, is altogether 

 impossible. 



Imagine, however, at each of the six corners of a regular octahe- 

 dron, a single molecule of marsh-gas, CH4, i.e. altogether C6H24, 

 and then imagine all the 24 hydrogen atoms successively removed, so 

 that each carbon atom is connected with each of its neighbour's only 

 by a single bond, and thus all six atoms of carbon are united together 

 in a single whole. Then you obtain, as the most simple represent- 

 ation of the molecule of the diamond, a regular octahedron, with 

 one atom of carbon at each of its six corners, while the edges repre- 

 sent the mutual bonds : — 



Vol. XYIII. (No. 99) 



