ETHYLENE, or Ethene, C2H4, or H2C:CH2, the first representative of the series of olefine hydrocarbons, is found in coal gas. It is usually prepared by heating a mixture of ethyl alcohol and sulphuric acid. G. S. Newth (Jour. Chem. Soc., 1901, 79, p. 915) obtains a purer product by dropping ethyl alcohol into syrupy phosphoric acid (sp. gr. 1.75) warmed to 200° C., subsequently raising the temperature to 220° C. It can also be obtained by the action of sodium on ethylidene chloride (B. Tollens, Ann., 1866, 137, p. 311); by the reduction of copper acetylide with zinc dust and ammonia; by heating ethyl bromide with an alcoholic solution of caustic potash; by passing a mixture of carbon bisulphide and sulphuretted hydrogen over red-hot copper; and by the electrolysis of a concentrated solution of potassium succinate,
It is a colourless gas of somewhat sweetish taste; it is slightly soluble in water, but more so in alcohol and ether. It can be liquefied at −1.1° C., under a pressure of 4212 atmos. It solidifies at −181° C. and melts at −169° C. (K. Olszewski); it boils at −105° C. (L. P. Cailletet), or −102° to −103° C. (K. Olszewski). Its critical temperature is 13° C., and its specific gravity is 0.9784 (air = 1). The specific gravity of liquid ethylene is 0.386 (3° C.). Ethylene burns with a bright luminous flame, and forms a very explosive mixture with oxygen. For the combustion of ethylene see Flame. On strong heating it decomposes, giving, among other products, carbon, methane and acetylene (M. Berthelot, Ann., 1866, 139, p. 277). Being an unsaturated hydrocarbon, it is capable of forming addition products, e.g. it combines with hydrogen in the presence of platinum black, to form ethane, C2H6, with sulphur trioxide to form carbyl sulphate, C2H4(SO3)2, with hydrobromic and hydriodic acids at 100° C. to form ethyl bromide, C2H5Br, and ethyl iodide, C2H5I, with sulphuric acid at 160–170° C. to form ethyl sulphuric acid, C2H5·HSO4, and with hypochlorous acid to form glycol chlorhydrin, Cl·CH2·CH2·OH. Dilute potassium permanganate solution oxidizes it to ethylene glycol, HO·CH2·CH2·OH, whilst fuming nitric acid converts it into oxalic acid. Several compounds of ethylene and metallic chlorides are known; e.g. ferric chloride in the presence of ether at 150° C. gives C2H4·FeCl3·2H2O (J. Kachtler, Ber., 1869, 2, p. 510), while platinum bichloride in concentrated hydrochloric acid solution absorbs ethylene, forming the compound C2H4·PtCl2 (K. Birnbaum, Ann., 1868, 145, p. 69).