Nitrogen . . 



1 



2 



3 



Halogens . . 



1 





3 



Uranium . . 





2 



3 



Vanadium . . 







3 



Manganese 





2 





Osmium &c. . 





2 





298 Mr. J. F. Heyes on Valency, 



of integers and not decimal residues*. It is only in respect 

 to our standard reference gas-molecule HC1', where hydrogen 

 and chlorine are said to be monovalent, that the valencies of 

 oxygen and nitrogen atoms in the comparable molecules can 

 be said to be divalent and trivalent, i. e. dyads and triads f. 

 In face of the enormous difficulties presented by " molecular 

 compounds,''' we are apt to forget that all chemicals consist 

 of chiefly heterogeneous and rarely of homogeneous com- 

 pound molecules; and a rush has, as it were, been made to 

 dispose of them by giving numerous valencies to either the 

 non-metallic or the metallic atom supposed to dominate all 

 the rest. Thus, Wurtz latterly assigned different valencies in 

 different compounds to 



5 



5 7 



5 



5 



Analogous high valencies have been suggested by Prof. 

 Williamson and others for many rare metals of high atomic 

 weights ; but in this case the halogens were taken as monads. 

 Both views have the same underlying principle. In the one 

 case a Peter dominates the Pauls, in the other a Paul domi- 

 nates the Peters. Both involve what I have pictured as the 

 maypole theory. Oxygen atoms dance round nitrogen or 



* The logical alternative is, I find, well put in a remarkable paper on 

 Atomic Valency by Prof. Pickering (Journ. Chern. Soc. 1886) : — " The 

 valency of hydrogen being 1, that of oxygen will be represented by some 

 number slightly smaller than 2, say 1-98 ■ a compound of these two elements 

 will possess a residual valency of only O02, and will therefore be sufficiently 

 saturated to be perfectly stable. It may be represented thus : (H 2 O)+ " 02 ." 

 He therefore treats " valencies " as '• not whole numbers/' but "similar 

 to most other physical constants, e. g. atomic weights, specific weights." 



t A distinction should be drawn between this provisional definition of 

 a frwalent element and the proposition advanced in Prof. Armstrong's 

 paper (page 24) that " the gasefiable hydrogen compounds are the only 

 compounds available for the direct determination of valency." Un- 

 doubtedly our present standard of reference is H'Cl' as a comparable 

 molecular formula ; but it seems only fair, on the principle of reciprocity, 

 not to leave the valency of metals to turn upon their few compounds or 

 alloys with another gaseous metal hydrogen (see my former paper, page 

 225). The caution that, in the case of the halides, XH„ does not neces- 

 sarily involve a valency of X' 1 is most important, and will, it is to be 

 hoped, lead to some investigations into the existence and chemical 

 habitudes of nuclei and ring-forniulse of nitrogen or nitrogen and carbon, 

 chlorine, iodine, oxygen, &c. 



