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You can make an electrician mad in the
same way by interrupting his explanation of a dynamo by asking: "But you
cannot tell me what electricity really is." The electrician does not
care a rap what electricity "really is"--if there really is any meaning
to that phrase. All he wants to know is what he can do with it.
[Illustration: COMPARISON OF COAL AND ITS DISTILLATION PRODUCTS From
Hesse's "The Industry of the Coal Tar Dyes," _Journal of Industrial and
Engineering Chemistry_, December, 1914]
The tar obtained from the gas plant or the coke plant has now to be
redistilled, giving off the ten "crudes" already mentioned and leaving
in the still sixty-five per cent. of pitch, which may be used for
roofing, paving and the like. The ten primary products or crudes are
then converted into secondary products or "intermediates" by processes
like that for the conversion of benzene into aniline. There are some
three hundred of these intermediates in use and from them are built up
more than three times as many dyes.


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