FUNDAMENTAL CONCEPTIONS 215 



fore obtain ethylene quantitatively from chloride or bromide of ethyl 

 by simply passing their vapors through tubes heated to the decompo- 

 sition-point. Nevertheless, it is impossible to obtain more than very 

 small amounts of ethylene from the ethylhalides by means of alcoholic 

 potash, caustic potash, or quicklime; in these cases ethylether or 

 ethylalcohol is the chief product even when the ethylhalide is passed 

 over quicklime in tubes heated from 300 to 500. Furthermore, 

 the per cent of ethylene obtained varies remarkably with the tem- 

 perature, the concentration, and with the nature of the halogen in the 

 alkylhalide used. The conclusions finally reached from these data 

 and also from an exhaustive study of the behavior of the various 

 alkylhalides, nitrates, sulphates, alkylpotassium-sulphates towards 

 heat, sodium ethylate, caustic potash, quicklime, and other salts, are 

 that ethylene cannot possibly be a primary product of dissociation 

 of the ethylhalides, sulphates and nitrates and of free ethylalcohol. 

 The ethylene, when obtained, is formed from ethylidene by an intra- 

 molecular addition reaction, 

 H 



I / I I 



CH 2 -CH^->CH 2 -CH 2 ^CH,=CH 2 , 



which is not reversible. 



A similar intramolecular change always, in fact, takes place when- 

 ever an olefine is formed, whether from a primary or secondary alcohol 

 or from a corresponding alkylhalide sulphate or nitrate. This trans- 

 formation is perfectly analogous to the conversion, discussed above, of 

 trimethylene and of propylene oxide into propylene, propionaldehyde 

 and acetone. 



When ethylalcohol or ethylether is heated to its dissociation-point 

 the ethylidene interacts at once in great part with the other dissocia- 

 tion-product, water, to give hydrogen and acetaldehyde, 



CH S CH/+O=H 2 ->CH S CH:O+2H. 



In the case of ether, since there are two ethylidene molecules to 

 one of water, the atomic hydrogen is in part absorbed by ethylidene 

 to give ethane. Finally, a portion of the ethylidene, 20 and 37 per 

 cent respectively, is transformed, by intramolecular addition, into 

 ethylene. The most striking proof that ether is dissociated into water 

 and two C 2 H 4 particles is the following : on passing ether vapor over 

 phosphorous pentoxide at temperatures varying from 200 to 400 

 ethylene is formed quantitatively. 



The primary and secondary alcohols and their corresponding ethers 

 being in a state of very slight dissociation at ordinary temperatures, 

 we are able to understand perfectly their behavior towards oxidizing 

 agents. The alkylidenes are all spontaneously combustible substances 



