It is still further true that acetylene, at some pressures, greater than
normal, has under most favorable conditions for the effect, been found to
explode; yet it may be stated with perfect confidence that under no
circumstances has anyone ever secured an explosion in it when subjected to
pressures not exceeding fifteen pounds to the square inch.
Although not exploded by the application of high heat, acetylene is injured
by such treatment. It is partly converted, by high heat, into other
compounds, thus lessening the actual quantity of the gas, wasting it and
polluting the rest by the introduction of substances which do not belong
there. These compounds remain in part with the gas, causing it to burn with
a persistent smoky flame and with the deposit of objectionable tarry
substances. Where the gas is generated without undue rise of temperature
these difficulties are avoided.
_Purification of Acetylene._--Impurities in this gas are caused by
impurities in the calcium carbide from which it is made or by improper
methods and lack of care in generation. Impurities from the material will
be considered first.
Impurities in the carbide may be further divided into two classes: those
which exert no action on water and those which act with the water to throw
off other gaseous products which remain in the acetylene. Those impurities
which exert no action on the water consist of coke that has not been
changed in the furnace and sand and some other substances which are
harmless except that they increase the ash left after the acetylene has
been generated.
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