Chapter 2

The filtrate is then poured into a cylinder capable of holding 100 cubic centimeters, and furnished with a scale; sufficient distilled water is then added until the well-shaken fluid measures precisely 100 cubic centimeters. By means of this measuring instrument, the filtrate is then divided into two equal portions. One of these parts is in a beaker glass over-saturated with chemically pure chloride of ammonia, whereby any iron of oxide present and a little dissolved alumina fall down as deposit. The precipitate is separated by filtering, washed, dried at 212° Fahrenheit and weighed. To the filtrate is then added a solution of oxalate of ammonia until a white precipitate of oxalate of lime is formed. This precipitate is separated by filtering, washed, dried and when separated from the filter, is collected upon dark satinized paper; the filter itself is burned and the ash added to the oxalate of lime. This oxalate of lime is then heated to a dark red heat in a platinum crucible with lid until the oxalate of lime is converted into carbonate of lime. By the addition of a few drops of carbonate of ammonia solution and another slight heating of the crucible, also the caustic lime produced in the filter ash by heating, is reconverted into carbonate of lime, and after cooling in the exsiccator, the whole contents of the crucible is weighed as carbonate of lime, after deducting the known quantity of filter ash.

Any magnesia present in the filtrate of the oxalate of lime is by the addition of a solution of phosphate of soda separated as phosphate of ammonia and magnesia, after having stood twenty-four hours. The precipitate is filtered off, washed with water to which a little chloride of ammonia is added, dried, and after calcining the fiber and adding the filter ash, glow heated in the crucible. The glowed substance is weighed after cooling, and is pyrophosphate of magnesia, from which the magnesia or carbonate of magnesia is calculated stoichiometrically. All the ascertained sums must be multiplied by 2, if they are to correspond to the analyzed and weighed quantity of ash.

The second half of the filtrate is used for determining the small quantity of sulphate of lime still contained in the hydrochlorate solution. By adding chloride of barium solution the sulphuric acid is bound to the barytes and sulphate of baryta separates as white precipitate. This is separated by filtering, washed, dried and weighed in the customary manner. From the weight of the sulphate of baryta is then computed the weight of sulphate of lime, which has passed over into solution. The ascertained sum is also to be multiplied with 2.

The manufacture of roll tar paper from the roll paper was at first found to be difficult, as it was impossible to submerge a surface larger than from ten to fifteen square yards, rolled up, in the tar, because more would have required too large a pan. Besides this, the paper tears easily, when it is in the hot tar. All kinds of experiments were tried, in order to impregnate the surface of the paper without employing too large a pan.

The following method was tried at first: The roll paper was cut into lengths of ten yards, which were rolled up loosely, so that a certain space was left between the different coils. These loose rolls, of course, occupied much space and could be put into the tar only in a standing position, because in a horizontal one the several coils would have pressed together again. The loose roll was therefore slipped over a vertical iron rod fastened into a circular perforated wooden foot. The upper end of this iron rod ended in a ring, in which the hook of a chain or rope could be fastened. With the aid of a windlass the roll was raised or lowered. When placed in the pan with boiling tar, it was left there until thoroughly saturated. It was then taken out, placed upon a table, and the excess of tar allowed to drip off into a vessel underneath. After partially drying, the roll was spread out in open air, occasionally turned, until sufficiently dried, when it was rolled up again.

In order to neutralize the smeary, sticky condition of the surface and avoid the disagreeable drying in open air, the experiment of strewing sand on the sticky places was tried next. The weight of the paper was largely increased by the sand, and appeared considerably thicker. For this reason the method of sanding the paper was at once universally adopted. To dispense with the process of permitting the surplus tar to drip off, means were devised by which it was taken off by scrapers, or by pressing through rollers. The scrapers, two sharp edged rods fastened across the pan, were then so placed that the paper was drawn through them. The excess of tar adhering to its surface was thereby scraped off and ran back into the pan.

This work, however, was performed better and to more satisfaction by a pair of rollers fastened to the pan. These performed a double duty; thoroughly removed the tar from the surface and by reason of their pressure they caused a more perfect incorporation of the tar with the fibers of the paper. Finally, different factories employed different methods of manufacture, one of which was to cut the rolls into definite lengths of about ten yards; these were then rerolled very loosely and immersed in the hot tar until sufficiently saturated. The paper was then passed through the roller, much pressure exerted, and then loosely rolled up again. Being tarred once, it was then laid into a second pan with hot tar, reeled out after a time, strewn with sand, and rolled up again. Another method was to cut clothes lines into lengths of about fifteen yards, and at a distance of two inches have knots tied in them. The paper was cut in lengths of ten or fifteen yards, three pieces of the knotted clothes line were then rolled between the loose coils of paper, which was then submerged in the tar, which on account of the knots could penetrate the paper. The paper was next sanded by permitting its lower surface to pass over dry sand in a box standing on the floor. A workman rolled off the paper, and with his hand he strews sand on the upper surface. The 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 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 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 made to improve the coal tar, it may be concluded that this material does not fully comply with its function of making the roofing paper perfectly and durably waterproof. The coal tar, be it either crude or distilled, is not a perfect impregnating material, and the roofing paper, saturated with it, possesses several defects. Let us in the following try to ascertain their shortcomings, and then express our idea in what manner the roofing paper may be improved. It was previously mentioned that every tar roofing paper will, after a greater or smaller lapse of time, assume a dry, porous, friable condition, caused by the volatilization of a part of the constituents of the tar. This alteration is materially assisted by the oxygen of the air, which causes the latter to become resinous and exerts a chemical influence upon them. By the volatilization of the lighter tar oils, pores are generated between the fibers of the roofing paper, into which the air and humidity penetrate. In consequence of the greatly enlarged surface, not only the solid ingredients of the tar, which still remain unaltered, are exposed to the action of the oxygen, but also the fibers of the roofing paper are exposed to decomposition. How destructive the alternating influence of the oxygen and the atmospheric precipitations are for the roofing paper will be shown by the following results of tests. It will have been observed that the rain water running from an old paper roof, especially after dry weather, has a yellowish, sometimes a brown yellow color. The supposition that this colored rain water might contain decomposition products of the roofing paper readily prompted itself, and it has been collected and analyzed at different seasons of the year. After a period of several weeks of fair weather during the summer, rain fell, and the sample of water running from a roof was caught and evaporated; the residue when dried weighed 1.68 grammes. It was of a brownish black color, fusible in heat and readily soluble, with a yellow brown color in water. The dark brown substance readily dissolved in ammonia, alcohol, dilute acid, hydrochloric acid, sulphuric acid, and decomposed in nitric acid, but did not dissolve in benzine or fat oil. After several days' rain during the summer, a quantity of the water was caught, evaporated, and the residue dried. Its characteristics were similar to those above mentioned. By an experiment instituted in water under conditions similar to the first mentioned, the dry brown substance weighed 71 grammes. It possessed the same characteristics. In the solution effected with water containing some aqua ammonia of the brown substance, a white precipitate of oxalate of lime occurred when an oxalate of ammonia solution was added, but the brown substance remained in solution. A further precipitation of oxalate of lime was produced by a solution of oxalic acid, but the brown organic substance remained in solution. This organic substance being liberated from the lime was evaporated, and left a dry, resinous, fusible brownish black substance, which also dissolved readily in water. It will be seen from these trials that the substance obtained from the rain water running from a paper roof is a combination of an organic acid with lime, which readily dissolves in water, and that also the free organic acid combined with the lime dissolves easily in water.