16 Mr. M. M. P. Muir on Chemical Notation. 



of molecules. The relative weights of molecules are there- 

 fore assumed to be represented by our chemical symbols. In 

 order to deduce such weights with accuracy, we are obli ged to 

 determine the relative densities of the substances in the form 

 of gas. and to assume the truth of the law of Gay-Lussac or 

 of Avogadro. But this law can be deduced from the mole- 

 cular theory of matter ; hence, when we speak of " molecular 

 weights," we assume the truth of the molecular theory ; and I 

 therefore think that it behoves us to know what this theory 

 really is, and on what physical grounds it can be upheld. 



34. I have already stated that the ordinary chemical nota- 

 tion does not appear to me to necessitate the assumption of 

 the existence of molecules ; but, granting that matter has a 

 molecular structure, this notation will readily lend itself to the 

 needs of such a theory. Can we, however, with equal facility 

 explain the general phenomena of chemical action in terms of 

 the molecular theory of matter ? 



35. The definition of a " molecule" quoted from Prof. Clerk 

 Maxwell's work does not prevent one from imagining an inner 

 structure for such molecules. We may think of one of these 

 little parts which holds together while the body to which it 

 belongs is hot as made up of a greater or less number of still 

 smaller parts, parts either of the same or of different kinds of 

 matter. In the conception of such smaller parts we have the 

 idea of chemical atoms. Now it may legitimately be supposed 

 that during the excursions which molecules are ever making, 

 some of them will be so knocked about as to have their atomic 

 structure disarranged ; under ordinary circumstances this dis- 

 arrangement will quickly be restored ; but if a new force be 

 called into play which shall act by increasing the tendency to 

 molecular disaggregation, we shall have a more or less com- 

 plete decomposition of the original molecules, attended, of 

 course, with the production of new molecules. The electro- 

 lysis of liquids may be regarded as a directive action exercised 

 by electromotive force upon those molecules which have un- 

 dergone disaggregation by clashing together, whereby one com- 

 ponent part of the disaggregated molecule is directed in one 

 direction, and another in another direction. 



36. So also the phenomenon of dissociation meets with an 

 explanation in terms of the molecular theory by supposing 

 that at high temperatures the clashing of molecules is carried 

 on so violently that more molecules suffer decomposition in a 

 unit of time than are able to regain their original structure. 

 Dissociation is then explained as a " change in the configura- 

 tion and motion of a material system." 



37. If this view of intramolecular action be adopted, we 



