Scientific American Supplement, No. 821 | Page 8

black lacquer. The
paper is sanded in a very simple manner without the use of mechanical
apparatus; as it is being wrapped into a coil, it passes with its lower
surface over a layer of sand, while the workman who tends to rolling up
strews the inside with sand. The lower surface is coated very equally.
Care only being necessary that the sand lies smooth and even at all
times. When the workman has rolled up ten or fifteen yards, he cuts it
across with a knife and straightedge, so that the paper is cut at right
angles with its sides.
There are three different sorts of roofing paper, according to the
impregnating fluid used in its manufacture. The ordinary tar paper is
that saturated with clear cold tar. This contains the greatest amount of
fluid ingredients and is very raggy in a fresh condition. It is easy to see
that the volatile hydrocarbons evaporate in a short time, and when
expelled, the paper becomes stiffer and apparently drier. This drying, or
the volatilization of the hydrocarbons, causes pores between the fibers
of the paper. These pores are highly injurious to it, as they facilitate a
process of decomposition which will ruin it in a short time.
Roofing paper can be called good only when it is essentially made from
woolen rags, and contains either very few or no earthy additions. It is
beyond doubt that the durability of a roofing paper increases with the
quality of wool fiber it contains--vegetable fibers and earthy additions
cause a direct injury. Reprehensible altogether is any combination with
lime, either in form of a carbonate or sulphate, because the lime enters
into chemical combination with the decomposition products of the tar.
The general nature of gravel is too well known to require description.
The grains of quartz sand are either sharp cornered or else rounded
pieces of stone of quartz, occasionally mixed with grains of other
amorphous pieces of silica--such as horn stone, silicious slate, carnelian,
etc.; again, with lustrous pieces of mica, or red and white pieces of
feldspar. The gravel used for a tar paper roof must be of a special

nature and be prepared for the purpose. The size of its grains must not
exceed a certain standard--say, the size of a pea. When found in the
gravel bank, it is frequently mixed with clay, etc., and it cannot be used
in this condition for a roof, but must be washed. The utensils necessary
for this purpose are of so simple and suggestive a nature that they need
not be described. Slag is being successfully used in place of the gravel.
It is easily reduced to suitable size, by letting the red hot mass, as it
runs from the furnace, run into a vessel with water. The sudden chilling
of the slag causes it to burst into fragments of a sharp cornered
structure. It is next passed through a sieve, and the suitably sized gravel
makes an excellent material, as it gives a clean appearance to the roof.
The thinking mind can easily go one step further and imagine that,
since the tar contains a number of volatile hydrocarbons, it might be
made more adaptable for impregnation by paper by distilling it, as by
this process the fluid would lose its tendency to evaporate and the
percentage of resinous substances increase. Singular to say, there was a
prejudice against the employment of distilled tar, entertained by
builders and people who had no knowledge of chemistry. Increasing
intelligence and altered business circumstances, however, brought
about the almost universal employment of distilled tar, and every 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