of the Metallic Oxides. 107 



A difference of the same kind exists between the oxides 

 and the corresponding carbonates, thus : — 



(MgO ... 

 lMgC0 3 . 



|ZnO 



lZnC0 3 ... 



|OaO 



lOaCOg .. 



fSrO 



lSr0O 3 ... 



fPbO 



\PbC0 3 ... 



/BaO 



lBaC0 3 ... 



Periclase 



3-65 

 2-99 to 3-15 



6-00 

 4-3 to 4-45 

 3-08 to 3-2 



2-7 



2-9 



461 



3-6 

 9*2 to 9-5 



657 



54 



4-28 



Griobertite 



Crystallized 



Smithsonite 





Calcspar .. 



Arragonite 



Strontianite 





Cerusite 





Witberite 





The great difference observed between the density of certain 

 oxides and that of their basic anhydrous salts is equally 

 worthy of note, thus : — 



Molecular weight. Density. 



216 10-69 



728 6-444 



HgO . . 



(HgO) 3 S0 3 



A study of the oxides, from both a physical and chemical 

 point of view, leads, therefore, to the general conclusion, that 

 for the most part the oxides cannot be compared with the 

 chlorides ; that the true oxides which are really comparable ivith 

 the chlorides are unknown ; and that we possess only polymers 

 thereof (RO*) w . 



Value of the Coefficient of Polymerization. 



What, now, is the true value of the coefficient n of polyme- 

 rization ? What is the real molecular formula of these 

 polymeric oxides? These questions are doubtless of great 

 interest, but it should be stated at once that it is absolutely 

 impossible to give an exact answer. I do not know of any 

 fact which would allow us to assign an absolute value to the 

 coefficient n of polymerization, for we are in exactly the same 

 position in respect to the metallic oxides as we are in the case 

 of the solid polymeric ones of organic chemistry, e. g. 

 methylene oxide, metaldehyde, &c. So far as facts will per- 

 mit of a conclusion, we may affirm that in most cases this 

 number is very high, although different for different oxides. The 

 molecular weight of most oxides should therefore be consider- 

 able. This conclusion results from a consideration of certain 

 facts previously referred to, and to which it will be necessary 

 to return for a moment. 



