Popular Science Monthly/Volume 22/December 1882/American and Foreign Asphalts
By E. J. HALLOCK.
BITUMINOUS substances, apparently of organic origin, are found in various parts of the world. Sometimes they occur in a free state, as in the Island of Trinidad, and at others impregnating calcareous rocks, or serving as a cement to hold the particles together, as at Val de Travers or Seyssel.
For several reasons the asphalt lake in Trinidad possesses special interest for us. The island, which is the southernmost of the Lesser Antilles, lies off the northern coast of South America, and is easily accessible from any of our sea-ports. Here, amid the most luxuriant vegetation, is a lake three miles in circumference, on the surface of which lies a crust of asphaltum of such tenacity that in the rainy season a person can walk across it; but, under the influence of the hot sun, it softens to a thick tar. This crust receives accessions from beneath, and formerly it would overflow and run into the sea, more than two miles away. A similar substance, known as "Jew's pitch," is washed ashore in considerable quantities around the borders of the Dead Sea. In Texas, south of Shreveport, there is said to be a pitch-lake containing large quantities of bitumen, but little is yet known about it. In Southern California there are accumulations of asphalt on the coast at Santa Barbara, San Luis Obispo, etc., which resembles, when pure, that from Trinidad. It promises to supply the wants of the western coast, as Trinidad will that of the eastern part of this country.
In Kentucky there is a considerable quantity of asphaltic mineral which may some time be utilized for road-making.
An interesting and valuable asphaltic mineral, known as Albertite, is found in New Brunswick; and a similar one, called Grahamite, occurs in West Virginia and other parts of the country. In the mountains west of Denver, in Colorado, is a vertical bed of hard and brittle asphalt, not unlike Grahamite, while Albertite is found in small quantities in Lorain County, Ohio, and Casey County, Kentucky.
Bitumen is likewise found in Cuba, and is brought into commerce under the name of chapopote, or Mexican asphalt.
In Europe asphalt occurs chiefly in limestone, which forms, when crushed and packed, an excellent pavement. The principal points at which it is found are the following: Val de Travers, in the Swiss Canton of Neufchâtel, fourteen miles from Neufchâtel, and sixteen or seventeen miles by rail from the French borders; Seyssel, on the Rhône, in the French department of the Ain, about thirty-three miles from Geneva; Lobsann, a small town in northern Alsace; Vorwohle, in Braunschweig; and Limmer, near the city of Hanover. The Italian province of Caserta, in the neighborhood of Naples, supplies Rome with an asphalt much used for terraces and flat roofs.
The quantity of bitumen in these limestones and the manner of its dissemination are quite varied, but it is generally found that the softer limestones contain more bitumen than those which are harder. The average amount is about ten per cent, but it sometimes reaches twenty or thirty per cent, and occasionally there are cavities in the rock which are filled with bitumen. At other times the quantity sinks to five per cent, or less, while nodules of limestone entirely free from it are also found. The value of the rock depends on the percentage of bitumen, and on other circumstances. If the stone is to be used for making mastic, the higher the percentage the more valuable it is; but, if used directly for paving, a uniform distribution, not exceeding eight or ten per cent, is desirable.
Asphalt-stone, to which Malo limits the name of asphaltum, varies in color from gray to brownish-black, according to the richness in bitumen; that of medium quality closely resembles chocolate in color. That which is poor in bitumen is hard, and rings like ordinary limestone; but the fatter rock, when struck with a hammer, gives forth a dull thud, like a block of wet plaster, and takes an impression from the blow. If it contains more than ten per cent, it crumbles in the hand, and can be cut with a knife, like chocolate. Good stone, with about ten per cent of bitumen, has a specific gravity of 2·1. Some asphalt-stone is of a spongy, hygroscopic nature, and consequently lighter.
One peculiarity of the natural rock-asphalt is that, when heated over a fire, it breaks up into a brown powder, and then, at a higher temperature, all the bitumen is expelled, leaving a pure white powder. An unsuccessful attempt was made in the Paris Conservatoire des Arts et Métiers to imitate this asphalt-stone by forcing thick, pasty bitumen into pure limestone by great pressure. When, however, the lime-stone was boiled for a long time in a liquid mass of asphalt, it became so completely saturated with it that the innermost fractures resembled the natural asphalt-stone; but it differed from the latter in. this most important property, that it did not crumble to a powder when heated. On the contrary, the absorbed bitumen was expelled by heat, leaving a hard limestone, instead of a calcareous powder. From this it seems probable that the particles of the natural asphalt stone are simply cemented together by the bitumen, and both must have been deposited at the same time.
In most mines the strata dip slightly toward the horizon. They vary greatly in thickness; sometimes there is only one stratum, at others there are several superimposed on each other or separated by strata of harder limestone or shale. At Val de Travers the strata that are worked are from two to six metres thick, and rest on hard, non-bituminous limestone.
In some places it is mined in open trenches, in others by means of shafts and subterranean tunnels. At Val de Travers, Seyssel, and Lobsann, the latter alone are employed. The rock is blasted out with powder, which works better in soft rock than dynamite. The holes are bored with an ordinary hand-auger. At Limmer, owing to the water in the mines, it is necessary to use dynamite.
The percentage of bitumen in the different varieties of asphalt stone is as follows: That from Limmer, 14·3; Val de Travers, 10·15; Lobsann, 12·32; Ragusa, 8·92; Seyssel, 8·15; Vorwohle, 8·50. It is estimated by extracting it from the finely pulverized mineral with carbon disulphide, benzene, or other solvent, and weighing the residue after the solvent has evaporated. The quality of the bitumen is determined by heating it to 430° or 440° Fahr.; the less it loses by evaporation the better its quality. The powdered mineral from which the bitumen has been extracted should be white and soft. If it has a gray color, and feels harsh or sticky, it is of poor quality. Too much dependence can not be placed on chemical analyses, for much depends on the physical properties as well.
The larger portion of the asphalt-stone used in Europe comes from Val de Travers, which produces about 25,000 tons a year; Limmer is not much inferior in its yield, which amounts to about 21,500 tons; Seyssel furnishes 13,000 tons, and Lobsann about 9,000 tons. That which is mined at Limmer and Vorwohle, being very rich, is only used for making mastic.
The first operation to which the asphalt-stone is subjected, when it reaches the factory, is pulverization. For this purpose several different machines are in use, the ordinary stone-breaker being unsuited to the purpose. Four or five of these are figured in Professor Dietrich's new work on "Asphalt Streets," to which we are indebted for many of the facts in this article.
The powder thus obtained may be employed directly for the pressed asphalt pavements, or converted into "mastic" by mixing it with one tenth to one seventh its weight of purified bitumen from Trinidad and cooking five or six hours. It is then poured into cast iron molds without bottoms, which are placed on the sanded floor of the shop. These blocks of mastic are fifteen inches in diameter and four inches thick, weighing fifty or sixty pounds each. Those made at Val de Travers are hexagonal in form, bearing a trade-mark of a cross and t; those from Seyssel and Lobsann circular; the others oblong, with rounded corners.
The Val de TraVers mastic and asphalt rock are imported by the Neufchatel Asphalt Company (54 Astor House, New York); the Seyssel mastic by the New York Mastic Works (35 Broadway); the Limmer and Vorwohle rock asphalt by C. Wichtendahl (111 Broadway, room 97). In regard to their uses in this city we shall speak more fully in another place.
Trinidad asphalt is imported and refined by the Warren Chemical and Manufacturing Company (45 John Street). This substance, as it occurs in nature, is very impure; about one third of the mass consists of water, another third is made up of clay and sand, so that only one third is actually bitumen. It is melted in large kettles and heated for twelve hours to expel the water, the earthy constituents settling to the bottom. This partially purified asphalt, which still contains about twenty per cent of impurities, is poured through a sieve into barrels, where it solidifies. It now forms a brittle mass, which sells for twenty-five dollars per ton. It is too hard for mixing with the pulverized asphalt-rock, or for street pavements. At Val de Travers and Seyssel the residues from the distillation of bituminous shale, known as "shalegrease," are used to soften it, while in other places similar residues of paraffine manufacture or petroleum refining are added to the natural bitumen to form what is known as "prepared bitumen," or mineral tar. In this country the so-called "still-bottoms" from petroleum-stills are used in the proportion of fifteen parts of the latter to eighty-five of the natural asphalt; the portions may be varied to suit the climate and other conditions.
Asphalt pavements may be divided into three classes. The first, which is commonly known as mastic (asphalte coulé), is best adapted to sidewalks, court-yards, and other places where there is but little heavy traffic. It is prepared by melting the blocks of mastic, already described, in caldrons, adding a small quantity of prepared bitumen, and afterward stirring in thirty or forty per cent of clear grit. When thoroughly mixed it is carried to the spot in pails, and spread with a wooden float by a skilled workman on his knees. It is then rubbed until perfectly smooth, and fine sand strewed over it. Examples of this pavement can be seen in Union Square, Tompkins Square, and several other places in New York city.
Compressed asphalt is better adapted to heavy traffic, as in street pavements, and is much employed in Paris. The powdered rock is used without any addition. It is applied hot, on a prepared bed of concrete, four to seven inches thick, and compressed, with heated rammers and a heated roller, to the thickness of one and a half or two inches. The smooth surface is given by a. heated smoothing-iron. One block of compressed Val de Travers asphalt, two inches thick, laid on a Portland cement concrete foundation seven inches thick, may be seen on Fifth Avenue, between Twenty-sixth and Twenty-seventh Streets.
The third form of pavement, which seems to be one of the best for roadways, is the "Trinidad." It is made of prepared bitumen, i. e., Trinidad asphalt and still-bottoms, mixed with about twice its weight of calcareous marl or powdered limestone. None of the imported asphalt mastics or rock are used in this pavement.
Various imitations of both asphalt and mastic have been palmed off on the public, or substituted by dishonest contractors, some of whom will keep a few blocks of real mastic of a well-known brand lying about, as if they were to be used, while inferior materials are thrown into the caldrons. Some imitations are but little inferior to the genuine, while others are nearly worthless, and have done much to bring asphalt into disrepute. Among the latter are those made in whole or in part of the pitch left in the distillation of coal-tar. Although useful for a great variety of purposes, it will not answer for asphalt pavements. It is usually possible to distinguish good bitumen by its smell when warmed. When heated with excess of concentrated or fuming sulphuric acid for twenty-four hours, and then diluted and filtered, the pure natural bitumen yields a nearly colorless solution, but if pitch is present the solution will be dark-brown or black. Another distinction between real bitumen and coal-tar is found in the solubility of the latter in alcohol, the former being nearly insoluble. If a grain of material that has been heated to 200° C. is pulverized and mixed with 5 c. c. of strong alcohol, the latter will acquire a yellow color and bluish-green fluorescence if there is more than two per cent of pitch present.
There are several uses to which asphalt may be applied, the most important being the one already so often referred to, namely, as paving material. In Paris about thirty-three miles of street are covered with asphalt pavement, more than three fourths of it being the so-called "compressed asphalt," while the remainder is made of cast or mastic asphalt. The use of asphalt pavements for roadways began in Paris in 1854, since which time their use has been steadily increasing until the present time. In London there are about nine miles of asphalted streets. Asphalt pavements have but recently begun to find favor in Berlin, and at the close of 1881 there were only six miles of street paved with it. Of asphalt sidewalks, etc., Paris has three million square metres, equivalent to four hundred miles of walks, seventeen feet wide. New York city can boast of only a few small and isolated strips of asphaltic street pavement, her past experience with the "poultice pavement" having induced the authorities to prohibit the laying of similar pavements. In front of the Brevoort House, and the Hotel Brunswick, samples of compressed pavement may be seen, while the American mastic, or Trinidad, has recently been laid in Fifteenth Street, between Fifth and Sixth Avenues. In Washington, D. C, more than forty miles of the last-named pavement have been put down, and it is said to be doing good service. There are a large number of the mastic sidewalk and court-yard pavements in this city, some of which have already been referred to.
The advantages claimed for asphalt pavements are cleanliness, noiselessness, and durability, while the wear and tear of horses and wagons is less, and they are the pleasantest of all pavements to ride on. On the other hand, they are often slippery, and horses are liable to fall on them, while they are more difficult to repair when broken in digging for water and other pipes, although it is said that water-pipes are less liable to freeze under asphalt than under other pavements.
Asphalt does not emit sparks when struck with steel, and therefore is useful for the flooring of powder-magazines, and of casemates in fortifications.
As damp-proof coating for vaults and cellar-walls it is invaluable, for, not only does it shut out damp from below, but prevents unhealthy exhalations of the soil from entering the dwelling.
Asphalt has been used as flooring in stables, although there has been some complaint that it is cut by the stamping of the animals. It would seem to be an excellent material for the purpose, as it is unacted upon by urine, and, being without cracks, prevents the liquids from passing through and saturating the earth beneath. It is in use in the stables of the American Horse Exchange, Fifty-sixth Street and Broadway.
Asphalt floors have found more extensive use in breweries and sugar-refineries, for which they seem perfectly adapted. It is frequently applied to cellar-bottoms in city houses, some careful citizens having covered their cement floors with asphalt mastic.
A method of laying floors is much used in France, for barracks and hospitals, which would probably answer for many other purposes. Pieces of oak, usually two and a half to four inches broad, twelve to thirty inches long, and one inch thick, are pressed down into a layer of hot asphalt, not quite half an inch thick, in herring-bone pattern. The edges of the blocks are planed down, beveling toward the bottom, thus insuring adhesion to the asphalt, and the smallest possible joints.
A coarse sort of canvas saturated with bitumen is used to prevent dampness from rising through capillary attraction and penetrating the walls of buildings, especially light-houses and marine structures. It is made in strips twelve, sixteen, twenty, or twenty-four inches wide, to correspond with walls made of three, four, five, or six courses of brick. Its superiority to ordinary bitumen depends on the fact that it will not crack, like the latter, from unequal settling of the walls. Damp resisting solutions are also sold for coating damp walls.
Asphalt mastic is much superior to tar for roofing purposes, owing to its fire-proof qualities, and its use for this purpose is rapidly increasing. At the present writing it is being applied to the Welles Building, at the lower end of Broadway. It is said that, when a building covered with such a roof burns, the falling roof acts like a blanket in smothering and extinguishing the flames.
Asphalt possesses another valuable property, that of absorbing vibrations, and is hence useful for foundations of machinery running at high speeds. A block of bituminous concrete weighing forty-five tons formed the foundation of the Carr's disintegrator which made fourteen hundred revolutions per minute at the Paris Exhibition. It would seem to be especially adapted to serve as foundations for the high-speed steam-engines used for generating electricity.
Asphalt forms an excellent insulator for electricity, but, as other and cheaper materials may be employed, its use will not be so extensive in this field.
The origin of asphalts is unknown, but several theories have been advanced in regard to it. Professor J. S. Newberry believes that they are the more or less perfectly solidified residual products of the spontaneous evaporation of petroleum. If we accept this theory (and many do not), we are but one step nearer a solution of the problem, for the origin of petroleum itself is still unknown. Some think that the bitumen was formed first, and the limestone deposited in it; others, that the liquid bitumen was forced into the pores of limestone already in existence; while a third hypothesis assumes that they were formed simultaneously, the bitumen from the organic matter, and the lime from the shells of some ancient mollusks. The last-named theory seems to have some support in the abundance of fossil ammonites met with in the mines at Limmer; the experimental attempts to impregnate the rock artificially, as above described, render the second hypothesis improbable, although its occurrence on the Dead Sea and in Trinidad is in its favor. No explosive gases are met with in the mines of Val de Travers, Seyssel, and Lobsann, so that open lights are used; but at Pechelbronn, a few miles from Lobsann, several explosions have occurred. Although these were attributed to marsh-gas, they were more probably due to the vapors of the lighter constituents of petroleum, with which the bituminous sands of that locality seem to be saturated.
There are several circumstances which indicate that bitumen and asphalt are more nearly related to petroleum than to coal-tar, and that, whether asphalt was made from petroleum or not, they have a similar or common origin. Nor is it an unfortunate circumstance that coal-tar can not be used as a substitute for bitumen, since the former contains many constituents that are more valuable for other purposes, while Trinidad offers an inexhaustible supply of the latter.