Spent lime of a yellowish brown colour is
frequently to be met with in circumstances that are clearly no reproach
to the generator. Doubtless the tint is due to the presence of some
coloured metallic oxide or other compound which has escaped reduction in
the electric furnace. The colour which the residual lime afterwards
assumes may not be noticeable in the dry carbide before decomposition,
either because some change in the colour-giving impurity takes place
during the chemical reactions in the generator or because the tint is
simply masked by the greyish white of the carbide and its free carbon.
Hence it follows that a bad colour in the waste lime removed from a
generator only points to overheating and polymerisation of the acetylene
when corroborative evidence is obtained--such as a distinct tarry smell,
the actual discovery of oily or tarry matters elsewhere, or a grave
reduction in the illuminating power of the gas.
MAXIMUM ATTAINABLE TEMPERATURES.--In order to discover the maximum
temperature which can be reached in or about an acetylene generator when
an apparatus belonging to one of the best types is fed at a proper rate
with calcium carbide in lumps of the most suitable size, the following
calculation may be made.
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