MOLECULAR ARCHITECTURE 369 



or to an alternative value, i : r4i42, this value depending 

 upon which direction in the horizontal plane of the assemblage 

 (fig. 3) is chosen for the "«" translation. The following are 

 the known hexagonal elements with their crystalline constants : 



It can be concluded that these elements are correctly or 

 very approximately correctly represented by the hexagonal 

 closest-packed assemblage of equal spheres. But the authors 

 of the theory are not content with stating that the observed 

 axial ratios approximate to the ideal values in the crystals of 

 the above elements ; they seek an explanation and make some 

 suggestions to explain why the observed slight discrepancies 

 occur. For example, after studying the case of glucinum, 

 they discover that if one-fourth of the spheres in the hexagonal 

 assemblage be considered slightly greater than the rest (these 

 greater spheres being symmetrically situated) and the packing 

 be made close by compressing the layers, then an assemblage 

 is obtained having rt :^ = i : 1*5802, the value observed for 

 glucinum. Of course, beyond the fact that the crystallographic 

 constants can be thus explained, there is no evidence to show 

 that such a state of affairs {i.e. the special treatment of certain 

 atoms) may exist in the crystal ; it is significant that the digres- 

 sions of all the other elements from ideal axial ratios can be 

 explained by some such slight modification. 



Among the elements the crystals of which are neither cubic 

 nor hexagonal are sulphur, selenium, tin and iodine. Sulphur 

 is remarkable in that it is known in four crystalline modifications, 

 one orthorhombic, two monosymmetric and one anorthic, this 

 last being rather doubtful. The axial ratios of one monosymmetric 

 form are particularly striking, being a\h\c — 0*9958 : i : 0*9998, 

 /3 = 95°46'.^ The close approximation of these numbers to the 

 cubic values a\b:c — \ \\ w, ^ = 90°, is obvious and it will be 

 admitted that but a very slight distortion of a cubic assemblage 



' Mitscherlich, Atuu Chem. Phys. 1823, 24, p. 264. 



