Such tar contains a
great number of hydrocarbons--naphtha, naphthalen, anthracen, phenol,
several organic alkaloids, hydrosulphuric and hydrocyanic acids, etc.,
all of which are more or less volatile at the temperature to which
they must have been subjected. These exhalations have proved fatal to
plant life when in sufficient quantity. We do not know of a better
remedy than that of removing the cause. Painting the pipes with a
strong solution of washing soda and lime would, in a measure, prevent
the escape of the most objectionable constituents into the air, by
forming with them compounds non-volatile at any temperature to which
they are likely to be subjected in contact with the pipes; but the
former would be the surest plan.
(4) C.D.W. asks: The roof of the new Illinois State House, as well as
the stylobate cornices and upper portion of the dome, are covered with
zinc. It has been on about three years, and I am told is materially
affected by oxidation. The theory is that zinc, though subject to
oxidization, has the peculiarity that the oxide does not scale off as
from iron, but forms a permanent coating impervious to the action of
the atmosphere. Some mechanics, however, assert that neither zinc,
copper, nor lead will withstand the action of our atmosphere, as
bituminous coal strongly impregnated with sulphur is almost the only
fuel used.
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