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



monly accepted meaning of the phrase. That amount of a 

 given radicle which will displace unit weight of hydrogen 

 from an acid may not be that amount which will do some 

 other kind of work, just as that amount of hay which will 

 displace 1 cubic foot of air in the railway truck is not that 

 amount which will do the work of an equal volume of bullion 

 in so far as exchange is concerned, although it does accomplish 

 the same amount of work when we define the unit of work as 

 " replacing 1 cubic foot of air." Dr. Mills has introduced an 

 unfortunate word by using the term value. 



15. If we for a moment agree to view this matter of valency 

 in the light of the molecular theory of matter, and of some 

 recent researches of Michaelis and other chemists, the ex- 

 planation given of the relation between valency and general 

 chemical "value" would be something as follows. We may 

 imagine the molecule of a chemical element performing a 

 certain vibration in a definite period of time ; during the 

 performance of this vibration there are certain positions at- 

 tained by the molecule, at each of which it is so situated as to 

 be capable of exercising chemical action upon other molecules. 

 The number of these positions is the valency of the molecule. 

 But we can suppose that the total force exercised is not 

 uniformly distributed, so that an unequal amount is capable of 

 being exercised at each position; hence the valency may vary 

 according to the reactions in which the molecule takes part. 

 Again, it is clear that the total force exercised will not neces- 

 sarily bear a simple relation to the number of positions in 

 wdiich the molecule may be capable of exercising this force ; 

 hence the general affinity (or chemical " value ") of a mole- 

 cule may be small, while its valency is large, or vice versa. 



16. Altogether, then, I think we have in valency a most 

 useful means of classification, and that we are fully entitled to 

 use the term " equivalent " in the acceptation generally as- 

 signed to it by chemists. This, however, does not prevent us 

 from admiring Dr. Mills's proposal to determine the power of 

 doing work, in terms of a fixed unit, of classes of chemical 

 substances. Undoubtedly such investigations would be highly 

 interesting, and would lead to most important results ; but 

 why we need do away with the advantages gained in order to 

 gain further advantages I, for one, am at a loss to determine. 

 Dr. Mills has himself made some very careful and elegant 

 experiments, by which he has determined the " dynamic 

 equivalent" of various nitrates in terms of a fixed unit. It 

 would be well that these researches should be extended. 



But when we are in the possession of a large amount of 

 such information as this ; surely it will not be necessary to 



