On the Intimate Structure of Crystals. 297 



treatment ; these are calcium, magnesium, and stannous oxides. The 

 metals calcium and magnesium undergo a considerable amount of 

 condensation on entering into combination ; it will therefore be more 

 convenient to select stannous oxide as the compound which is to serve 

 as the basis for obtaining the relative diameter of oxygen ; but this 

 course is not without its disadvantages, for very different values have 

 been found by different experimenters for the specific gravity of 

 stannous oxide, and the same is true of the metal tin itself, which 

 further has the additional defect of crystallising, not in the cubic, 

 but in the tetragonal system. 



Tin. At. w., llS'l ; sp. gr., 7'0 to 7*5 ; mean, 7*25 (taken). 



Gross atomic volume, 16*29 ; volume of atomic sphere, 8*53. 



Diameter of atom, 2*535. 

 Stannous Oxide, SnO. M. w., 134*1 ; sp. gr., 6*1 (Nordenskjold), 



6-6 at C. (Berzelius, Ditte). The latter value is taken. 



M. v., 20-313. Volume of four molecules, 81'273. 



Edge of cubelet or diameter of SnO 4*3316 



Diameter of one atom of Sn 2*535 



O 1*8508 



Gross volume of oxygen, 6'34 ; volume of atomic sphere, 3*32. 



Calcium oxide, CaO. M. w., 56 ; sp. gr., 3'251 ; m. v., 17'25. 

 Volume of four molecules, 17'25x4 = 68'9. 



Edge of cubelet or diameter of CaO 4'100 



Diameter of one atom of O 1*851 



Ca 2*27 



Gross volume of Ca, 11*695. The gross volume of Ca in the 

 metallic state is 25*48. 



Periclase, MgO. M. w., 40*38 ; sp. gr., 3'636 ; m. v., 11*105. 

 Volume of four molecules, 44*423. 



Edge of cubelet or diameter of MgO .... 3*5416 



Diameter of one atom of O 1*851 



Mg 1-6936 



Gross volume of Mg, 4*858. The gross volume of Mg in the 

 metallic state is 14*341. It crystallises in the hexagonal system. 

 These results are more or less uncertain ; it must be borne in mind 

 that the volume of oxygen differs greatly in different compounds. 



The metals which remain for consideration in the present com- 

 munication are as follows : 



