406 MODERN GASWORKS PRACTICE
The bond between the carbon atoms tends to break away, whilst two hydrogen atoms also escape, thus decomposing the molecule into three distiuct portions, nameIyCH2, CH2, and H2. Ethane thcn has yielded [2 (CH2) + Ha], whicli on recombination may become either
(1) C2H4 (ethylene) + H2,
or (2) 2 C + 2 H2 + H2,
and by hydrogenation, i.e. + H2, we get
(3) 2 CH j (methane).
In the same way ethylene has a tendency to split up across the double carbon bond into the following residues:—
H H ,
Etliylene = H— C^C — H = [2 (CH) + HJ.
I '
These then reunite to yield—
(1) C2H2 (acetylene) + H2 (hydrogen),
or(2) 2 C +H2 +H2,
or (3) by hydrogenation (i.e. +2 H2) = 2 CH4 (methane). . __
With regard to acetylene, the change may take place either by polymerization, as already mentioned, or by dissolution into residues. In the latter case a weakness develops across the triple bond between the carbon atoms
X /
Acetylene = B— C C — H = 2 (rzz CH).
The CH residues then give—
(a) 2 C 4- Ha,
or (b) by hydrogenation (i.e. +3 H2) = 2 CH4 (methane).
Tliere is little doubt that in addition to degradation a certain amount of Synthesis takes place at definite temperatures in the retort. The increase in the quantity of methane at higher temperatures is in all probability due to this cause. Burgess and Wheeler, in their well-known. work, state that evolution of hydrocarbons of the paraffin series ceases almost entirely at temperatures above 700° C.; but at the same time there are certain indications of an increase in the methane above this point. Pring and Fairlie, in a contribution to the proceedings of the Chemica Society, state that results of their experiments show that at temperatures betv een 700° and 730° C. acetylene reacts with hydrogen to give methane and ethylene. At a temperature of 1,200° C. carbon, was found to combine with hydrogen to gi^e both methane and ethylene, the rate of formation, of the methane being 100 times that of the ethylene. A certain amount of acetylene was also formed at this temperature, but the quantity was too small to be measured.
Some of the most enlightening work on the behaviour of the hydrocarbons has been carried out by Cobb and Hollings, at Leeds University. In this instance