Laws of Molecular Force. 267 



the value of M 2 / for any substance to obtain the number of 

 CH 2 groups to which its molecule is equivalent as regards 

 molecular force. 



11. Definition of the Dynic Equivalent of a substance, and 

 determination of its value for several Radicals. — In the manner 

 just described were obtained the numbers entered in Table 

 XXV. under the heading S, which I propose to call the 

 Dynic Equivalents of the substances. The dynic equivalent 

 of a molecule is the number of CH 2 groups in the molecule of 

 the normal paraffin that exerts the same molecular force as it. 



The table shows that the atom of an element contributes 

 the same amount towards the dynic equivalent of all molecules 

 in which it occurs (except in the case of the simpler typical 

 compounds) : thus, for example, consider the iodides from 

 methyl to amyl iodide, and notice that each CH 2 group has 

 the same value unity as in the paraffins, and that the iodine 

 atom is equivalent to about 2'30H 2 in every case. The same 

 law holds throughout the table ; so that each elementary atom 

 or radical has its own dynic equivalent, which can be easily 

 determined. 



In the first place, it appears that the extra H 2 in the 

 paraffins C n H 2?l+2 can be neglected in a first approximation, 

 because C 5 H 10 has practically the same dynic equivalent as 

 C 5 H 12 , and C 8 H 16 the same as C 8 H 18 . It may be that the 

 double binding in the unsaturated compounds compensates 

 for the H 2 of the saturated, but I think that the simpler idea 

 for the present is that the two terminal H atoms in a paraffin 

 chain have a dynic equivalent so small that we may neglect 

 it, or more generally the middle H in a CH 3 group is negligible 

 in a first approximation. If there is really such a difference 

 between the middle H and the two others in CH 3 , we ought 

 to find the dynic equivalents for the iso- compounds smaller 

 than for the normal ; and the table shows that the isobutyrates 

 have equivalents smaller by *1 than the butyrates, while the iso- 

 butyl salts of the fatty acids have dynic equivalents nearly all 

 less than 1 greater than the propyl salts. But this is rather a 

 matter for the chemist to work out in detail ; it suffices to 

 indicate the idea here, and to point out that it is in harmony 

 with the lowering of boiling-points among isomers with in- 

 creasing number of CH 3 groups. Accordingly, as a matter of 

 detail, in the estimation of the dynic equivalents of the elements, 

 it was assumed that the equivalent of C H H., ft+2 , w H 2h + 1 , and 

 C n H 2ji is in each case n when normal and n — 'lj) when the 

 molecule departs from normality by p CH 3 groups. (In 

 constructing my curve for dynic equivalents, for the sake of 



T2 



