10 Mr. William Sutherland on the 



elements and CH 4 . It is very remarkable that as regards 

 molecular force, CH 4 not only detaches itself so completely 

 from the paraffins and compounds in general, but also attaches 

 itself so consistently to the elements. It is interesting to find 

 C 2 H 4 , which is the first of the olefines, detach itself from its 

 class; in the " Laws of Molecular Force " it was proved to 

 have a characteristic equation intermediate in form to those 

 for elements and compounds. It has already been pointed 

 out that the olefine C«H 2n has the same value of (M 2 Z)*as the 

 paraffin C 7l H 2n +2 ; but this does not apply to C 2 H 4 , because 

 instead of the 4*0 for C 2 H 6 , it has the value 2*5 for (M 2 /) 5 , and 

 lor M/3 it has 43, which is much larger than the 34 of two 

 ordinary CH 2 groups ; the ratio M/3/(M 2 /)* is 17, which goes 

 with the values found for CH 2 and CH 4 . 



The case of the elements will be returned to when the 

 methods of getting further data have been developed in the 

 following parts of this paper. 



To close for the present the discussion of the carbon serial 

 compounds, the main result had better be restated, as it has 

 perhaps been obscured by foreign details ; it is embodied 

 briefly in Table IV., and is this, that the attracting-power of 

 a molecule is the sum of powers belonging to its atoms, the 

 power of an atom varying with its chemical function, but 

 remaining constant when that function is constant. As a 

 subsidiary result, it has been shown that the attracting- 

 powers of the atoms of CI, Br, I, 0, S, N, and C (C unattached 

 to H) are approximately proportional to their volumes in the 

 combined state. 



2. (a) and (b). Methods of finding M 2 Z for Compounds of 

 the Metals, with Results. 



(a) While we are on the present line of investigation, it 

 will be convenient to consider such values (relative) of the 

 parameter of molecular force, that is of (M 2 Z) 5 , as are ob- 

 tainable for solids, both element and compound. These can 

 be got in two ways : first, from the surface-tension of the 

 solids at their melting-points, which are still measurements 

 made on liquids, but at the transition-point into solidity; and 

 second, from the principles of "A Kinetic Theory of Solids " 

 (Phil. Mag. vol. xxxii.). According to the "Laws of Mole- 

 cular Force " (Phil. Mag. March 1893, p. 258), I in terms of 

 the 10 6 dynes as unit of force is given by 



Z=2x5930aw*M*, 

 where a. is the surface-tension in grammes weight per metre 



