resinous substances are increased thereby, still the light tar oils
remain to evaporate, and the paper prepared with such a substance
readily becomes hard and brittle. A better addition is the natural
asphaltum, because it resists better the destroying influence of the
decomposition process, and also, to a certain degree, protects the
coal tar in which it is dissolved. The addition of natural asphaltum
doubtless caused the name of "asphaltum roofing paper." Resin,
sulphur, wood tar and other substances were also used as additions;
each manufacturer kept his method secret, however, and simply pointed
out by high sounding title in what manner his paper was composed. In
most cases, however, this appellation was applied to the ordinary tar
paper; the impregnating substance was mixed only with coal pitch, or
else a roofing paper saturated with distilled tar. The costly
additions, by the use of which a high grade of roofing paper can
doubtless be produced, largely increased its price, and on account of
the constant fall of prices of the article, its use became rather one
of those things "more honored in the breach than in the observance,"
and was dispensed with whenever practicable. The crude paper is the
foundation of the roofing paper. The qualities of a good,
unadulterated paper have already been stated. At times, the crude
paper contains too many earthy ingredients which impair the cohesion
of the felted fibrous substance, and which especially the carbonate of
lime is very injurious, as it readily effects the decomposition of the
coal tar. The percentage of wool, upon which the durability of the
paper depends very largely, is very small in some of the paper found
in the market. In place of woolen rags, cheap substitutes have been
used, such as waste, which contains vegetable fibers. Since this
cannot resist the decomposition process for any length of time, it is
evident that the roofing paper which contains a noticeable quantity of
vegetable fibers cannot be very durable. To judge from the endeavors