of the Metallic Oxides. 



85 



forget that these molecules, as well as the formulae which 

 express them, are really only relative. We do not know, and 

 we shall never know, that which is truly and absolutely a 

 molecule, for we cannot and never shall be able to obtain one 

 singly and alone. We possess, and we shall always possess, 

 only groups of molecules. The character of reality which we 

 wish to give to our molecules and to our formulae is essentially, 

 then, a relative one. What we have to determine are real 

 relationships between real bodies. These relationships of 

 analogy and difference remain practically the same if, in the 

 impossibility of verifying them between the bodies them- 

 selves, we seek for them between the same bodies in a modified 

 condition ; modified simultaneously, however, and in a similar 

 manner. It results from these considerations that it is of 

 great importance to examine chemical phenomena from the 

 molecular point of view. To establish real molecular formulas 

 for bodies (i. e. formulae truly and universally comparable) is 

 therefore an object eminently worthy of attention. It is this 

 idea which has induced me to undertake a lengthened series 

 of theoretical and experimental studies on compounds in both 

 mineral and organic chemistry, and more particularly as 

 regards the metallic oxides. 



The Peculiar Character of the Metallic Oxides. 

 A comparative examination of the oxides and chlorides 

 leads to a general fact. Chlorides are fusible compounds, 

 and, with few exceptions, volatile. It has been long observed 

 that chlorine gives wings to the metals, as one may say. 

 Volatility is especially noticeable in the chlorides of the fixed 

 elements, and particularly of the metals. The corresponding 

 oxides, on the contrary, are distinguished by their fixity and 

 infusibility, either absolutely or relatively. The following 

 table shows that this difference is general: — 





Mole- 

 cular 

 weight. 



Physical 

 state. 



Fusibility. 



Volatility. ' 



JBOl, 



IB 2 3 



|Si01 4 



lSi0 2 



117 



70 



170 



60 



192 



82 

 231-5 

 121-5 

 260 

 150 

 189 

 134 



Liquid. 



Solid. 



Liquid. 



Solid. 



Liquid. 



Solid. 



Solid. 



Solid. 

 Liquid. 



Solid. 



Solid. 



Solid. 





Boils 17°. 



Fixed. 

 Boils 59°. 



Fixed. 



Boils 135°. 



Fixed. 

 Sublimable. 



Fixed. 

 Boils 115°-4. 



Fixed. 

 617°-628°. 



Fixed. 



Fuses 577°. 



\ Fusible in oxyhy-1 

 \ drogen flame. J 



(TiCl 4 



Itkx, 



Infusible. 

 Fusible. 

 Infusible. 



fZrCl 4 



lZr0 2 



1 SnCl 4 



lSn0 2 



fSnCL 



\SnO 



Infusible. 



2493. 

 Infusible. 





