But
if the temperature should rise much above the point at which benzene is
the most conspicuous product of polymerisation, other far more
complicated changes occur, and harmful effects may be produced in two
separate ways. Some of the new hydrocarbons formed may interact to yield
a mixture of one or more other hydrocarbons containing a higher
proportion of carbon than that which is present in acetylene and benzene,
together with a corresponding proportion of free hydrogen; the former
will probably be either liquids or solids, while the latter burns with a
perfectly non-luminous flame. Thus the quantity of gas evolved from the
carbide and passed into the holder is less than it should be, owing to
the condensation of its non-gaseous constituents. To quote an instance of
this, Haber has found 15 litres of acetylene to be reduced in volume to
10 litres when the gas was heated to 638 deg. C. By other changes, some
"saturated hydrocarbons," _i.e._, bodies having the general formula
C_nH_(2n+2), of which methane or marsh-gas, CH_4 is the best known, may
be produced; and those all possess lower illuminating powers than
acetylene. In two of those experiments already described, where Lewes
observed maximum temperatures ranging from 703 deg.
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