The richly illuminating vapours of benzene
and naphthalene (and homologues) cannot practically add to the
illuminative value of acetylene, because of the difficulty of consuming
them without smoke, unless they are diluted with a large proportion of
feebly- or non-illuminating gas, such as methane or hydrogen. The
practical effect of carburetting acetylene with hydrocarbon vapours will
be shown in Chapter X. to be disastrous so far as the illuminating
efficiency of the gas is concerned. Hence it appears that no conceivable
products of the polymerisation of acetylene by heat can result in its
illuminative value being improved--even presupposing that the burners
could consume the polymers properly--while practically a considerable
deterioration of its value must ensue.
The heat of combustion of acetylene was found by J. Thomson to be 310.57
large calories per gramme-molecule, and by Berthelot to be 321.00
calories. The latest determination, however, made by Berthelot and
Matignon shows it to be 315.7 calories at constant pressure. Taking the
heat of formation of carbon dioxide from diamond carbon at constant
pressure as 94.3 calories (Berthelot and Matignon), which is equal to
97.
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