interest in tar paper roofs, the method of manufacturing an
impermeable paper being already so far perfected that the squares of
paper were dipped in tar until thoroughly saturated. The roof
constructed of these waterproof paper sheets proved itself to be a
durable covering, being unimpenetrable to atmospheric precipitations,
and soon several factories commenced manufacturing the paper. The
product was improved continually and its method of manufacture
perfected. The good qualities of tar paper roofs being recognized by
the public, they were gradually adopted. The costly pine tar was soon
replaced by the cheaper coal tar. Square sheets of paper were made at
first; they were dipped sufficiently long in ordinary heated coal tar,
until perfectly saturated. The excess of tar was then permitted to
drip off, and the sheets were dried in the air. The improvement of
passing them through rollers to get rid of the surplus tar was
reserved for a future time, when an enterprising manufacturer
commenced to make endless tar paper in place of sheets. Special
apparatus were constructed to impregnate these rolls with tar; they
were imperfect at first, but gradually improved to a high degree. Much
progress was also made in the construction of the roofs, and several
methods of covering were devised. The defects caused by the old method
of nailing the tar paper direct upon the roof boarding were corrected;
the consequence of this method was that the paper was apt to tear,
caused by the unequal expansion of the roofing boards and paper, and
this soon led to the idea of making the latter independent of the
former by nailing the sides of the paper upon strips running parallel
with the gable. The use of endless tar paper proved to be an essential
advantage, because the number of seams as well as places where it had
to be nailed to the roof boarding was largely decreased. The
manufacture of tar paper has remained at about the same stage and no
essential improvements have been made up to the present. As partial