FUNDAMENTAL CONCEPTIONS 219 



H 

 CH.CH/ +H-OC 2 H 4 ->CH,CH/ 



OC,H S 



to give ether, and this process can naturally go on indefinitely. 



When ethyl alcohol is mixed with an excess of concentrated sul- 

 phuric acid and heated to 160 no ether but some ethylene is formed; 

 in fact this method is still suggested and used as the best means of pre- 

 paring ethylene. The yield of olefine, however, can never be raised 

 above 20 per cent of the theory, and the operation is extremely tedious 

 because carbonization and formation of sulphurdioxide takes place 

 to a very marked extent. These results are now easily understood. 

 The ethylidene molecules, formed by dissociation of ethylated sul- 

 phuric acid, burn chiefly at the expense of the oxygen present in 



sulphuric acid, CH 3 CH(^ +0 =SO 2 ^CH 3 CH:O+SO, and the result- 

 ing acetaldehyde is then at once charred by the vitriol present. Only 

 twenty per cent at the utmost of the ethylidene particles escape this 

 oxidation by intramolecular conversion to ethylene. 



Finally we may summarize the conclusions reached in the above 

 discussion as follows. The valence of carbon is not a constant. At 

 definite temperatures, which vary remarkably with the nature of the 

 groups bound to it, a carbon atom becomes spontaneously dyad. Be- 

 low these limits there is dynamic equilibrium between bivalent and 

 quadrivalent carbon. The existence of carbon compounds containing 

 bivalent carbon has been definitely established ; methylene chemistry 

 plays a great r61e in many of the fundamental reactions of organic 

 chemistry. The conception of substitution or metalepsis, which has 

 been our guide in interpreting the reactions of carbon chemistry since 

 1833 is no longer tenable. It must be replaced by the conception of 

 dissociation in its broadest sense. Fundamentally speaking, there 

 are but two classes of carbon compounds, the saturated and the 

 unsaturated compounds. Excluding reactions called ionic, a chemical 

 reaction between two substances always first takes place by their 

 union to form an addition product. The one molecule being unsatur- 

 ated and partially in an active molecular condition absorbs the 

 second molecule because it is partially split or dissociated into two 

 active portions. The resulting addition product then often dissociates 

 spontaneously, giving two new molecules. 



The similarity of such reactions to those called ionic is at once ap- 

 parent, but their relationship cannot in the present state of our know- 

 ledge be clearly understood. 



