rolling taking place on the edge of a table, by means of a crank, the excess of sand dropped off.

It is said by this method two workmen, one of which tends to the rolling and sanding, the other turning the crank, could turn out eighty rolls per day. This method is still in use. It is useless to describe the many antiquated methods in vogue in smaller factories, and it can truthfully be said that nearly all of them are out of date. It appears to be the fact of almost all inventions that when reduced to practical use, the arrangements, apparatus, and working methods employed are generally of the most complicated nature, and time and experience only will simplify them. This has been also the case with the methods in the roofing paper industry, which are at present gradually being reduced to a practical basis. The method gradually adopted has been described in the preceding. The pan is of a certain length, whereby it becomes possible to saturate the paper by slowly drawing it through the heated tar. This is the chief feature. The work is much simplified thereby and the workmen need not dip their hands into the tar or soil them with it. The work of impregnating has become much cleaner and easier, while at the same time the tar can be heated to a much higher temperature. The pan is generally filled with distilled coal tar, and the heating is regulated in such a manner that the temperature of the impregnating mass is raised far beyond 212° Fahrenheit. This accelerates the penetration, which takes place more quickly as the degree of heat is raised, which may be almost up to the boiling point of the tar, as at this degree the paper is not destroyed by the heat. In order to prevent the evaporation of the volatile ingredients of the tar, the pan is covered with a sheet iron cover, with a slot at the place where the paper enters into the impregnating mass and another at the place where it issues. The tar is always kept at the same level, by occasional additions.

The roll of paper is mounted upon a shaft at the back end of the pan, and by suitable arrangement of guide rollers it unwinds slowly, passes into the tar in which it is kept submerged. The guide rollers can be raised so that when a new roller is set up they can be raised out of the tar. The end of the paper is then slipped underneath them above the surface of the tar, when having passed through the squeezing rollers, it is fastened to the beaming roller, and the guide rollers are submerged again. A workman slowly turns the crank of the beaming roller.

This motion draws the paper slowly through the fluid, the roll at the back end unwinding. The speed with which the squeezing rollers are turned is regulated in such a manner that the paper remains sufficiently long underneath the fluid to be thoroughly impregnated with it. The workmen quickly learn by experience how fast to turn the crank. The hotter the tar, the more rapid the saturation; the high degree of heat expels the air and evaporates the hygroscopic fluid in the pores of the paper. The strong heating of the tar causes another advantage connected with this method. The surface of the paper as it issues from the squeezing rollers is still very hot, and a part of the volatile oils evaporate very quickly at this high temperature. The surface is thereby at once dried to a certain degree and at the same time receives a handsome luster, as if it had been coated with a 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 parts raw paper, 176.4 partially distilled tar. Experiments on a larger as well as a smaller scale