Laws of Molecular Force, 



287 



to be a mathematical impossibility that the modular or additive 

 principle should apply also to M 2 /cA _1 , rigorously ; or, more 

 accurately, if the modular principle applies rigorously to one 

 of the quantities cA _1 and M 2 /cA _1 it cannot apply rigorously 

 to the other : but practically we find such relations amongst 

 the nmnbers that both are approximately obedient to the 

 modular principle. The case of NH 4 casts some light on the 

 question, for with it cA _1 shows the same differences in the 

 values of the chloride, bromide, iodide, and nitrate as with 

 the other positive radicals, while M 2 /cA _1 does not do so : 

 this case would make it appear that the modular principle 

 applies rigorously to cA -1 , but not so rigorously to M 2 /cA -1 . 

 But leaving out of the count this case of NH 4 , significant as 

 it is, we can find mean values for the differences of the dynic 

 equivalents of all the metals and Li, and of all the negative 

 radicals and CI ; if we can obtain the absolute value of the 

 dynic equivalent of Li and of CI, we shall have those for all 

 the metals and radicals. Now from the organic compounds 

 we have already got a value 1*3 for the dynic equivalent of 

 CI, and hence from the value for LiCl we could obtain that 

 for Li. The value tabulated for LiCl is 2*1, but we can 

 obtain a mean value fairer to all the other bodies by sub- 

 tracting, for example, from the value for KI the mean difference 

 for K and Li, and for I and CI ; in this way we arrive at a 

 mean value 1*9 for LiCl, from which, taking the value 1*3 for 

 CI, we should get '6 for Li. Bot the refraction-equivalents of 

 the halogens are supposed by Gladstone to be a little larger 

 in inorganic than organic compounds ; so that in the light of 

 our previous knowledge of a close parallelism between dynic 

 equivalents and refraction-equivalents it might be safer to 

 assume that the dynic equivalents of Li and CI in LiCl are in 

 the ratio of their refraction-equivalents in that compound, 

 namely, 3' 8 and 107. According to this assumption the values 

 for Li and CI come out '5 and 1*4, which we will adopt as 

 true and use in the calculation of the dynic equivalents of the 

 elements given in the following Table. These are measured 

 of course as before in terms of that for CH 3 as unity, and, 

 again, for comparison there are written along with the dynic 

 equivalents the refraction-equivalents in terms of that for CH 2 

 as unity, calculated from Gladstone's values (Phil. Trans. 

 1870)/ 



