26 Mr. H. E. Armstrong on Valency, 



appear to apply in the case of hydrogen, and may be repre- 

 sented thus : — 



-e- * -e- = e— e 



H. H. H 2 . 



But if the atom be not easily penetrated by its charge, it will 

 not move out to the end of its line, and the resulting com- 

 pound molecule will possess more or less " residual affinity " ; 

 this conception would appear to apply to the non-metals 

 generally, and to some of the metals ; it may be illustrated 

 thus : — 



e- + -e 



H. CI. HC1. 



I have thought it permissible to state my views in this 

 form merely in order to advance the study of molecular 

 compounds by the introduction of a working hypothesis, an 

 absolutely artificial mode of expression such as is here adopted 

 being perhaps pardonable in the absence of any explanation 

 which may serve to guide us in extending our enquiries as 

 regards the structure of such compounds, a knowledge of 

 which is all important to a rational conception of the nature 

 of chemical change generally. Moreover, I do not hesitate 

 to affirm that, from the chemical point of view, it is impossible 

 to adopt the Helmholtz explanation of valency, unless physi- 

 cists are prepared to grant the possibility of the " division " 

 of the unit charge somewhat in the manner here suggested ; 

 and it is in order to impress this that I have ventured to give 

 utterance to these speculations. 



To return to the consideration of the compounds previously 

 referred to, it may be supposed that the nitrogen of trimethyl- 

 amine and the iodine of methyl iodide are possessed of residual 

 affinity, and hence the two molecules unite to form the 

 molecular compound tetramethylammonium iodide, which 

 may be represented thus : — 



H 3 C 



H 3 C— == — CH 3 



H 3 C 



The phosphonium and sulphine iodides may be regarded as 

 similarly constituted. It is well known that the ammonium 



