22 Mr. H. E. Armstrong on Valency, 



molecular attractions produced by the water and other con- 

 stituents of the fluid." The italics are mine. But if the 

 " minor molecular attractions " contribute to the electro- 

 motive force of the cell, then conversely these also will have 

 to be overcome in effecting electrolysis, and are as much to 

 be reckoned as are the " mutual affinities of the ions " ! 



It is obvious that if it should prove possible to decide what 

 number of charges are necessarily associated with any par- 

 ticular atom, the conception of valency will have acquired a 

 definiteness which cannot possibly be attached to it as long 

 as the views that have hitherto guided us are adhered to. A 

 decision must involve the discussion of the question of the 

 existence of molecular as distinct from atomic compounds. 



To cast the apple of discord without further preface, I 

 would direct attention to the insufficiency of the evidence on 

 which it is usual to rely as proof that nitrogen, for example, 

 is a pentad ; nay more, I would assert that this very evidence 

 should be interpreted as proof that nitrogen is not a pentad. 

 It is commonly held that the behaviour of the alkyl tetra- 

 substituted derivatives of ammonium is such as to negative 

 the idea that these are " molecular compounds " of triad 

 nitrogen, and that it must be assumed that the elements of 

 the binary compound which are added on to the ammonia 

 derivative are distributed in the ammonium derivative ; for 

 example, that in the formation of tetramethvlammonium 

 iodide from trimethylamine and methyl iodide, the methyl 

 and iodine of the iodide part company, and separately attach 

 themselves to the nitrogen, thus : — 



/CH 3 CH 3 CH 3 /CH 3 



N-CH 3 + I = ^>N-CH 3 



X CH 3 : 1 X CH 3 



But I contend that the properties of tetramethvlammonium 

 iodide and hydroxide prove that such is not the case : the 

 iodide, it is well known, can be boiled for hours with the 

 strongest caustic potash solution without undergoing chano-e; 

 there is not a single case on record, however, of any haloid 

 compound other than an alkylic compound behaving in this 

 manner, the chlorides, bromides, and iodides of every element 

 except carbon are almost at once converted into hydroxides 

 by such treatment, and a nitrogen iodide would surely be 

 acted on. The behaviour of the iodine is much more nearly 

 that of iodine in methyl iodide, and, it may be said, exactly 

 that of the iodine in iodobenzene ; indeed it would seem that 

 in the alkyl-ammonium haloid compounds the halogen is 



