Scientific American Supplement, No. 821 | Page 3

the wood cement roof, which is regarded as an offshoot.
The tar paper industry has, within the last forty years, assumed great dimensions, and the preferences for this roofing are gaining ground daily. In view of the small weight of the covering material, the wood construction of the roof can be much lighter, and the building is therefore less strained by the weight of the roof than one with the other kind, so that the outer walls need not be as heavy. Considering the price, the paper roof is not only cheaper than other fireproof roofs, but its light weight makes it possible for the whole building to be constructed lighter and cheaper. The durability of the tar paper roof is satisfactory, if carefully made of good material; the double tar paper roof, the gravel double roof, and the wood cement roof are distinguished by their great durability.
These roofs may be used for all kinds of buildings, and not only are factories, storehouses, and country buildings covered with it, but also many dwellings. The most stylish residences and villas are at present being inclosed with the more durable kinds; the double roof, the gravel double roof, and the wood cement roof. For factory buildings, which are constantly shaken by the vibrations of the machinery, the tar paper roof is preferable to any other.
In order to ascertain to what degree tar paper roofs would resist fire, experiments were instituted at the instigation of some of the larger manufacturers of roofing paper, in the presence of experts, architects, and others, embracing the most severe tests, and it was fully proved that the tar paper roof is as fireproof as any other. These experiments were made in two different ways; first, the readiness of ignition of the tar paper roof by a spark or flame from the outside was considered, and, second, it was tested in how far it would resist a fire in the interior of the building. In the former case, it was ascertained that a bright, intense fire could be kept burning upon the roof for some time, without igniting the woodwork of the roof, but heat from above caused some of the more volatile constituents of the tar to be expelled, whereby small flames appeared upon the surface within the limits of the fire; the roofing paper was not completely destroyed. There always remained a cohesive substance, although it was charred and friable, which by reason of its bad conductivity of heat protected the roof boarding to such an extent that it was "browned" only by the developed tar vapors. A fire was next started within a building covered with a tar paper roof; the flame touched the roof boarding, which partly commenced to char and smoulder, but the bright burning of the wood was prevented by the air-tight condition of the roof; the fire gases could not escape from the building. The smoke collecting under the roof prevented the entrance of fresh air, in consequence of which the want of oxygen smothered the fire. The roofing paper remained unchanged. By making openings in the sides of the building so that the fire gases could escape, the wood part of the roof was consumed, but the roofing paper itself was only charred and did not burn. After removing the fire in contact with the paper, this ceased burning at once and evinced no disposition whatever to spread. In large conflagrations, also, the tar paper roofs behaved in identically a similar manner. Many instances have occurred where the tar paper roof prevented the fire from spreading inside the building, and developing with sufficient intensity to work injury.
As it is of interest to the roofer to know the manner of making the material he uses, we give in the following a short description of the manufacture of roofing paper. At first, when square sheets were used exclusively, the raw paper consisted of ordinary dipped or formed sheets. The materials used in its manufacture were common woolen rags and other material. In order to prepare the pulp from the rags it is necessary to cut them so small that the fabric is entirely dissolved and converted into short fibers. The rags are for this purpose first cut into pieces, which are again reduced by special machines. The rags are cut in a rag cutting machine, which was formerly constructed similar to a feed cutter; later on, more complicated machines of various constructions were employed. It is not our task to describe the various kinds, but we remain content with the general remark that they are all based on the principles of causing revolving knives to operate upon the rags. The careful cleansing of the cut rags, necessary for the manufacture of paper, is not required for roofing paper. It is sufficient to rinse