ery
large factory uses it at present. The roofing paper prepared with
distilled tar is perhaps most suitably called asphaltum paper, as this
has been used in its manufacture. It possesses properties superior to
the ordinary tar paper, one of which is that immediately after its
manufacture, as soon as cold, it is dry and ready for shipment; nor
does it require to be kept in store for a length of time, and it has
also a good, firm body, being as flexible and tough as leather. It is
very durable upon the roof, and remains flexible for a long time. It
is true that asphaltum papers will always in a fresh state contain a
small percentage of volatile ingredients, which after a while make it
hard and friable upon the roof; but, by reason of its greater
percentage of resinous components, it will always preserve a superior
degree of durability and become far less porous. One hundred parts by
weight absorb 140 or 150 parts by weight of coal tar. A factory which
distilled a good standard tar for roofing paper recovered, besides
benzole and naphtha, also about ten per cent. of creosote oil, used
for one hundred parts raw paper, 176.4 partially distilled tar.
Experiments on a larger as well as a smaller scale reduced this
quantity to an average of 141.5 parts for one hundred parts raw paper.
The weight of sanded paper is very variable, as it depends altogether
upon the size of the sand grains. It may be stated generally that the
weight of the sand is as large as that of the tarred paper.

The kinds of roofing paper saturated with other additions besides coal
tar form a separate class, in order to neutralize the defects inherent
in coal tar. These additions were originally for the purpose of
thickening the paper and making it stiffer and drier. The most
ordinary and cheapest thickener was the coal pitch. Although the
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