of the Metallic Oxides. 109 



bear in mind the small difference which exists between the den- 

 sity of the oxides C w H 2 ,iO and that of their polymers (C w H 2?l O) 2 

 or (C n H 2n O) 3 , we are led to conclude that the coefficient n of 

 polymerization of the metallic oxides must be very high, in 

 order to raise the density of an oxide to nearly double that of 

 the corresponding chloride, as is frequently the case. 



Doubtless the molecular condensation is different with 

 different metallic oxides. A priori we should expect it to be 

 so. This is proved by the fact that the difference between the 

 fusibility, volatility, density, &c. of the oxides and the corre- 

 sponding chlorides is very different in the several cases. 



This condensation appears to attain its maximum in certain 

 fixed and very infusible oxides, such as silica and alumina 

 &c, the corresponding chlorides being eminently volatile. 

 This enormous condensation of their molecules may possibly 

 be the cause of the greater resistance which they offer to the 

 action of chemical agents, more especially to simple chemical 

 agents such as H, C, CI, S, &c. 



Origin and Mechanism of the Polymerization of the Oxides. 



What is the origin, or, rather, what is the mechanism, of this 

 molecular condensation which is so general in the oxides, and 

 yet so absent in the chlorides ? The diverse chemical nature 

 of the two elements accounts for the different molecular 

 behaviour of their compounds. 



Chlorine is essentially a monovalent element, whilst oxygen 

 is divalent. The result of this quality in oxygen is the pos- 

 sibility of its uniting by its two affinities with two polyvalent 

 radicals. 



From the atomic and molecular point of view, polymeri- 

 zation consists essentially in a simple change in which each 

 atom of oxygen becomes united to two different atoms of the 

 radical belonging to different molecules, and maintains them 

 permanently together as a whole. The conversion of acetic 

 aldehyde into its triple polymer, paraldehyde, is an interesting 

 example of this atomic migration : — 



CH 3 . CH— 0— CH . CH 3 



CH 3 . CH : O becomes \4 



CH 3 



Similar facts occur, and in a similar manner, in the case of 

 the metallic oxides, thus : — 



