472 CONSIDERATION OF CARBON COMPOUNDS. 



Olefins. The hydrocarbons of the general formula C n H 2n are 

 termed olefins. To this series belong : 



Ethylene or ethene C 2 H 4 . 



Propylene or propene .... C 3 H 6 . 



Butylene or butene C 4 H 8 . 



Amylene or pentene .... C 5 H 10 . 



Hexylene or hexene .... C 6 H 12 . 



Methene, CH 2 , the lowest term of this series, is not known. The 

 hydrocarbons of this series are not only homologous, but also poly- 

 meric with one another. 



Ethylene, C 2 H 4 (Ethene, olefiant gas), the first member of the 

 olefins, is of special interest on account of its normal occurrence in 

 illuminating gas made from coal, as also in most common flames, the 

 luminosity of which depends largely on the quantity of this compound 

 present in the burning gas. 



Besides destructive distillation there are several reactions by which ethylene 

 can be obtained. Of these two are of interest. The first one depends on the 

 action of an alcoholic solution of potassium hydroxide on ethyl chloride, bro- 

 mide, or iodide : 



C 2 H 5 Br + KOH = C 2 H 4 + KBr + H 2 O. 



This reaction shows the possibility of preparing an unsaturated compound 

 of the ethylene series from a saturated hydrocarbon ; and as the method is 

 applicable to compounds of other classes it furnishes the means to pass from 

 any saturated compound to the corresponding unsaturated compound of the 

 ethylene series. 



The second method for preparing ethylene depends on the dehydrating action 

 of sulphuric acid on ethyl alcohol : 



C 2 H 5 OH H 2 = C 2 H 4 . 



Ethylene combines directly with an equal volume of chlorine forming ethy- 

 lene dichloride, C 2 H 4 C1 2 , an oily liquid, whence the name olefiant gas. 



Amylene, C 5 H 10 . Of the three isomeric hydrocarbons of the composition 

 C 5 H 10 , two have been used medicinally. It is especially the amylene of the 



CH CH 



composition Qjj 3 ^>C = C<JT 3 i. e., trimethyl-ethylene which has been in- 

 troduced as an anaesthetic under the name of pental. It is formed from tertiary 

 amyl alcohol (amylene hydrate) by the action of dehydrating agents. It is a 

 colorless, very volatile liquid, insoluble in water, but miscible in all proportions 

 with chloroform, ether, and alcohol. It has a penetrating odor, reminding of 

 mustard oil. 



