If a mixture of acetylene with either of the oxides of carbon is led
through a red-hot tube, or if a similar mixture is submitted to the
action of electric sparks when confined within a closed vessel at some
pressure, a decomposition occurs, the whole of the carbon is liberated in
the free state, while the hydrogen and oxygen combine to form water.
Analogous reactions take place when either oxide of carbon is led over
calcium carbide heated to a temperature of 200 deg. or 250 deg. C., the
second product in this case being calcium oxide. The equations
representing these actions are:
C_2H_2 + CO = H_2O + 3C
2C_2H_2 + CO_2 = 2H_2O + 5C
CaC_2 + CO = CaO + 3C
2CaC_2 + CO_2 = 2CaO + 5C
By urging the temperature, or by increasing the pressure at which the
gases are led over the carbide, the free carbon appears in the graphitic
condition; at lower temperatures and pressures, it is separated in the
amorphous state. These reactions are utilised in Frank's process for
preparing a carbon pigment or an artificial graphite (_cf._ Chapter
XII.).
Parallel decompositions occur between carbon bisulphide and either
acetylene or calcium carbide, all the carbon of both substances being
eliminated, while the by-product is either sulphuretted hydrogen or
calcium (penta) sulphide.
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