2l6 



CHEMISTRY AND CRYSTALLOGRAPHY. 



with the inscriibed tetrahedron of 4 hydrogen atoms (turned 

 through 180° round the cube-diagonal), the whole system being 

 then distorted by compressing four of the carbon spheres round 

 a diagoniai point in upon one of the central 'hydrogen spheres, 

 and expanding the other four carbons so as to fit in the 

 other three central hydrogen spheres. Now wihen equal 

 spheres are in cubic order, each cavity is slightly smaller 



,than a spliere I'ia.: (8 — ^-j : --), and the density of 



the assemlblage is ~ , i.e., 52.4 per cent, of the space is 



Fig 2. — Benzene ModeL 



occupied. It follows that the introduction of the hydrogen 



must make Pope's final assemblage looser than >-, smce bcth 



the carbons and the four hydrogens together have a separate 



density of — ; consequentlv much compression will be required 

 12 



to eliminate the interstitial space. My own arrangement, on the 

 other hand, is essentially the same as the close-packed arrange- 

 ment of equal spheres described by Pope in earlier papers, sub- 

 ject only to the modifications introduced by (i) having the 



