xvn MOLECULAR ARCHITECTURE 435 



which represented carbonic oxide as displacing two atoms 

 of hydrogen in a double-water-type ; in doing this he sug- 

 gested that 



"One atom 1 of carbonic oxide is here equivalent to two 

 atoms of hydrogen, and by replacing them, holds together 

 the two atoms l of hydrate in which they are contained, thus 



necessarily forming a bibasic compound, ' x 2> cai> bonate 



of potash" (Journ. Chtm. Soc., 1852, 4, 353; reprinted 

 from the Chemical Gazette, 1851). 



Carbonic oxide was therefore, in Kekule's phraseology, a 

 dibasic or diatomic radical. 



Frankland, in the following year, in the memorable 

 paper in which he described a " New Series of Organic 

 Bodies containing Metals" (Phil. Trans., 1852, 417-444), 

 had put forward the conception of a definite COMBINING 

 POWER for each element : 



" When the formulae of inorganic chemical compounds 

 are considered, even a superficial observer is struck with 

 the general symmetry of their construction ; the compounds 

 of nitrogen, phosphorus, antimony and arsenic especially 

 exhibit the tendency of these elements to form compounds 

 containing 3 or 5 equivalents, of other elements, and it is 

 in these proportions that their affinities are best satisfied ; 

 thus in the ternal group we have NO 3 , 2 NH 8 , NI 8 , NS a , 2 

 P0 2 , 2 PH 3 , PCI,, Sb0 3 , 2 SbH w SbCl 3J As0 3 , 2 AsH 3 , AsCl a , 

 etc. ; and in the five-atom group NO 5 , 2 NH 4 O, 2 NH 4 I, 

 PO 5 , 2 PH 4 I, etc. Without offering any hypothesis regarding 

 the cause of this symmetrical grouping of atoms, it is 

 sufficiently evident, from the examples just given, that such 

 a tendency or law prevails, and that, no matter what the 

 character of the uniting atoms may be, the combining 

 power of the attracting element, if I may be allowed the 

 term, is always satisfied by the same number of these atoms 

 (foe. dt. p. 440). 



1 i.e. molecule, molecules. 



2 /.*. N 2 3 , N 2 S ? , P 2 S , Sb,0 3 . As 2 3 , N 2 O 5 , (NH 4 ) 3 O, P,O 5 , etc., 

 using modern atomic weights in place of Gmelin's equivalents. 



F F 2 



