24 Mr. H. E. Armstrong on Valency, 



sense that they are all less readily acted on by alkalies than are 

 the parent alkylic haloid compounds ; but just as these latter 

 are more readily attacked by alkalies and other agents the 

 more complex the alkyl, so are the tetralkyl ammonium 

 compounds ; in no case, however, do they manifest a reac- 

 tivity at all comparable with that of simple metallic or non- 

 metallic haloid compounds — always excepting those of 

 carbon. 



The argument used above would apply equally to the 

 phosphonium and sulphine compounds ; indeed with greater 

 force. 



In many other respects, the behaviour of nitrogen in 

 aminic compounds is altogether peculiar and irreconcilable 

 with the assumption of pentadicity. Thus it is commonly 

 pointed out that the basic properties of aniline, for example, 

 become lessened and ultimately almost annulled by the intro- 

 duction of chlorine or bromine into the phenyl radical ; and 

 that acetamide, C 2 H 3 . NH 2 , and other similar compounds 

 formed by the introduction of acid radicals into ammonia are 

 all but destitute of basic properties ; the power to form 

 ammonium compounds, therefore, is not a simple function of 

 the nitrogen atom, but is largely dependent on the nature of 

 the radicals associated with the nitrogen atom. Other illus- 

 trations are afforded by the hydrazines. Thus phenyl-hydrazine, 

 C 6 H 5 .NH.NH 2 , although it contains two atoms of (triad) 

 nitrogen, forms with hydrogen chloride the compound 

 C 6 H 5 . N 2 H 3 . HC1, which crj'stallizes unchanged from fum- 

 ing muriatic acid, in which, moreover, it is almost in- 

 soluble. Etkyl-hydrazine, however, forms a dichlorhydride, 

 C 2 H 5 . N 2 H 3 . 2HC1 ; but on evaporating the aqueous solution 

 of this salt a monochlorhydride is obtained ; and unsymmetric 

 diethyl-hydrazine, (C 2 H 5 ) 2 N . NH 2 , is a monobase like phenyl- 

 hydrazine. 



Hence it may well be argued that we have no reason to 

 assume that nitrogen is pentad in the ammonium compounds, 

 or phosphorus pentad in the phosphonium compounds, or 

 sulphur tetrad in the sulphine compounds ; but that these are 

 all to be reckoned as molecular compounds. 



What then is the valency of the elements in question ? and 

 what is a molecular compound ? 



In answer to the first of these questions, the proposition 

 may be advanced that gasefiable hydrogen compounds arc 

 the only compounds available for the direct determination ot 

 valency, and that the valency of an element — the number of 

 unit charges necessarily associated with its atom — is given by 

 the number of hydrogen atoms combined with the single atom 



