230 Mr. J. F. Heycs on the 



formula as K— Cl=(O s )" and K— C1=(0 4 )", where the 

 (0 3 ) and (0 4 ) are at present indeterminate bivalent radicals. 



There is of course no evidence at present available for the- 

 quadri valency of oxygen to be clearly derived from the oxides 

 of nitrogen. The means of determining whether N 2 is 



N \ 

 II y O as usually assumed, 



or I ""0, or HI are still wanting : 



but when any are given in our text-books the alternatives 

 should surely be given and the whole marked with a con- 

 spicuous ? 



It was in fact in the compounds already referred to, H 2 2 

 and Ba0 2 , that I at first concluded the tetra valency of oxygen 

 to be the lesser of two puzzles. I look upon them as 



H— 0— H 

 Ba=0=0 and H 2 =0=0, or || 



O 



allowing of course that neither are formulae of strictly com- 

 parable molecules. 



(i.) The peculiar reactions of Ba0 2 , Mn0 2 , Pb0 2 , and their 

 inability to form what are curiously called "corresponding 

 salts," as contrasted with Sn0 2 , Si0 2 , are suggested to me by 

 the formulae X"=O=0 as opposed to X IV 2 , i.e. 0=X=0, 

 the molecules being (X0 2 ) a , where x is unknown. 



(ii.) The existence of a series of oxides in the case of some 

 metals, and of only one oxide with others, is probably connected 

 with this double valency — I use the phrase provisionally as the 

 sequel will show — of oxygen. Some of the oxides are otherwise 

 not accounted for. and in others there is an assumed linking or 

 double linking of the metallic atoms of which we may well be 

 sceptical. For it is, I believe, the peculiar characteristic of 

 the non-metals or negative elements to preferably exhibit tin's 

 single, double, or treble linking (if it exists, and whatever it 

 may mean) and thus to accumulate. Thus the oxides of silver, 



Ag 4 0, Ag 2 0, Ag 2 2 , are taken as 



Ag 4 =0, Ag— 0— Ag, and Ag— 0— Ag. 



II 

 



Similarly, Hg and Cu being clearly defined divalent metals, 



