Popular Science Monthly/Volume 58/January 1901/Asphaltum for a Modern Street
|ASPHALTUM FOR A MODERN STREET.|
ASPHALTUM is the solid form of bitumen, as it occurs in nature. It has been known to man from prehistoric times. The word is said to be derived from ὰ privative, and σφάλλο 'I cause to slip.' It, therefore, signifies a substance that prevents one from slipping, and was applied to the solid forms of bitumen that soften in the sun. This substance was not rare in so-called Bible lands, embracing the Valley of the Euphrates, the table lands of Mesopotamia and the Valley of the Jordan. It was of frequent occurrence along the shores of the Dead Sea, and was gathered and sold in the caravan trade that passed through the land of Moab and Petrea into Egypt, where it was used in the preparation of mummies.
During the Middle Ages, asphaltum appears to have found but few uses, and is seldom mentioned. The words asphaltum, petroleum and naphtha appear to have been used with different meanings, and also interchangeably or synonymously; yet the words were generally used to signify a thing that was located and defined by further description, so that the bitumen of the Dead Sea was recognized as asphaltum or solid bitumen.
Within the present century, however, both words and definitions have been more exact. As other and slightly differing material was obtained that in some respects resembled coal, it was claimed that some of the deposits of bitumen were beds of coal, and this claim led, about 1850, to important litigation, in which, as experts, scientific men gave very conflicting testimony, one party claiming that the material of certain deposits was asphaltum, and the other that it was coal. It was finally decided that the material—the albertite of New Brunswick—was not coal, and, therefore, did not belong to the Crown. At about this time a deposit occurring in West Virginia, since known as Grahamite, which, in appearance, is much more like splint coal than albertite, attracted attention. There were veins of material in Cuba that were also included in the argument, Coal vs. Asphalt.
The late Dr. T. Sterry Hunt, as long ago as 1863, separated asphaltuni from pyrobituminous minerals, or minerals that on being heated to destructive distillation yield products that resemble bitumens. These pyrobituminous coals, schists and shales are nearly as insoluble in the solvents of bitumen, viz., ethyl ether, chloroform, benzole, etc., as they are in distilled water; hence, Dr. Hunt made the action of these solvents the test of the two classes of substances. All true bitumens are miscible with or almost wholly soluble in chloroform, a test that clearly separates them from pyrobituminous minerals. So-called 'asphaltic coals' are not coals at all, but are geologically old asphaltums.
Besides the asphaltums, almost wholly soluble in chloroform, there are a large number of minerals that consist only in part of true bitumens. These are found as beds of sedimentary or crystalline rock, often of immense extent and thickness, impregnated with bitumens of varyi inconsistency and quality, sometimes very soft and seldom quite solid after being separated from the rock. In some instances the bitumen appears to be convertible into asphaltum, and in others not. The French writers have called these rocks 'asphalte,' but, unfortunately, they have also called asphaltum by the same name, as if the things w r ere identical and the words synonymous. Among English writers no uniform custom prevails, but German authors use generally the French word, at the same time calling asphaltum 'Erdpech' or 'Glanzpech.' I think it would promote clearness of expression if this word 'asphalte' were uniformly introduced into all modern languages to designate those bituminous rocks, with the qualifying words, siliceous, calcareous or argillaceous, added as required.
The so-called Trinidad pitch, as it is found in and around the lake, on the island of Trinidad, is a mixture of bitumen, water, mineral and vegetable matter, the whole inflated with gas. When removed from the deposit, most of the water dries out, the gas escapes, the mass changes in color from brown to blue-black, becoming brittle, and at the same time more or less sticky as it loses water. At a rough estimate, about 25 per cent, of the natural cheese-pitch is bitumen.
Various theories have been formulated by scientific men to' account for the origin of asphaltum and other forms of bitumen. By some it is thought that complex chemical changes take place between water. •carbonate of lime and iron, and other elements that are supposed to exist in the free state or in combination with carbon as carbides, at great depths from the surface. When they have been formed they are supposed to rise towards the surface with steam and water. This is called the 'chemical' theory. Others think that organic animal and vegetable matter that has been buried in strata near the surface of the earth has been converted by a process of partial decay into bitumen. This is called the 'indigenous' theory. Others think that the natural heat of the crust of the earth generated by pressure and, perhaps, other causes, has distilled bitumens from pyrobituminous minerals, and, in some instances, from coal, and they have penetrated the surrounding and overlying porous formations, often filling crevices and forming veins, when the pressure becomes sufficient to rupture the overlying formations. I am inclined to think this latter theory, of 'distillation,' will best account for all the varying conditions under which the various forms of bitumen occur.
Bitumens occur in all periods of the geological history of the earth's crust, but are mainly confined to the formations anterior to the coal period and to the later formations of the tertiary. While asphaltum is found in some of the oldest formations, the greater number of the deposits of solid bitumen and bituminous rocks occur in the more recent formations.
In order to show graphically the relations of the pyrobituminous minerals to the various forms of bitumen, I have arranged the following table, which represents the development of our present knowledge of these substances from the time when M. Leon Malo first published a similar table about forty years ago:
While it might be interesting to describe in detail all the minerals mentioned in this table, we are at present concerned with only two, viz., asphaltums and asphaltes. Again, while it might be interesting to describe asphaltums and asphaltes from all the many localities in which they occur, we are at present concerned only with those in use in street paving, and particularly those in use in the United States.
It is said that the idea of constructing a roadway of asphalte was first suggested by the observation that lumps of asphalte that have dropped from carts upon a road, when trodden by animals and rolled beneath wheels, became compacted into a homogeneous and resisting surface. These observations were made in eastern France, in the valley of the Rhone, where very extensive deposits occur, extending into Switzerland. They were first brought into notice, about 1721, by Eirnis
d'Erynys, a Greek physician, who published a pamphlet in which were described deposits of sand and limestone saturated with bitumen that he had discovered some years previously in the Val de Travers, Canton of Neufchâtel, Switzerland. He described also a bituminous distillate which he used in the treatment of disease. He compared the deposits to similar beds in the valley of Siddim, near Babylon. They were forgotten for nearly a century and then re-discovered.
By whom this material was first used in road building is unknown. Early in 1850, M. de Coulaine published a paper in the ’Annales des Ponts et Chausses’ in which he discussed the use of bitumen in road building as if it was an established industry. He states, without giving any date, that the first attempt to construct a street of bitumen in Paris was made upon the Place Louis XV., opposite the Church of Saint Koch. This pavement was formed of fragments of quartz and of mastic of coal-tar, upon a bed of sandstone, the joints of which were filled with the mastic. These coal-tar streets, even with a concrete base, were not satisfactory, thus early establishing the undesirable qualities of coal tar preparations in the construction of streets.
He states his preference for the asphaltes found at Seyssel, Val de Travers and Lobsan, which are composed principally of carbonate of lime and bitumen or sandstone and bitumen. As found in nature, these asphaltes consist either of chalk, sandstone or coarser gravel which have been filled to saturation with bitumen, which when extracted or separated from the mineral constituents of the rocks, is semi-fluid, resembling mineral tar. The deposits occur in beds between more dense and barren rock, and are mined out by running galleries and tunnels
into the hills that border the valleys, in a manner similar to the mining of coal in some sections of country.
Other deposits of similar material occur at Ragussa, in Sicily, and at Limmer, in Hanover. The Seyssel and Neufchâtel rocks are generally preferred for streets, as they contain more lime and less sand, and are also freer from sulphur compounds.
On the North American continent there are deposits of vast extent both of asphaltum and asphaltes. Generally speaking, asphaltum is not used in street construction; the deposits being either too pure, and hence too valuable for such uses, or, on the other hand, so impure as to be purified only at too great cost. As the asphalte is used in enormous quantities, freight becomes a very important consideration in the selection of the material used in any given locality. This item of cost has given the deposit on the island of Trinidad very great importance as a source of supply for all the Atlantic Coast cities and even those as far west as Denver, while the Pacific Coast cities have been supplied from deposits in California, which to some extent have competed with Trinidad pitch, not only in the Mississippi Valley, but even in New York and other Eastern cities.
The deposits in Trinidad are comprised in the so-called lake and extensive masses outside of it that have either overflowed from the lake or have been derived from independent sources. In the aggregate the extent of the deposits can only be estimated, as their boundaries cannot be determined with any approach to accuracy. They amount, without any doubt, to several millions of tons.
While I have classed the Trinidad pitch with the asphaltes, it is really a unique substance. I have elsewhere called it 'Parianite,' from
the beautiful bay of Paria, near the coast of which the deposit occurs. The lake is a lake only in name; the deposit, without doubt, filling the crater of an old mud volcano. As described for more than a century preceding 1890, it exhibited an expanse of about one hundred and fourteen acres, with a nearly circular outline, in which irregular areas of pitch are separated by smaller areas of water. Around the borders of the lake, vegetation, commencing at some distance from the edge, is rooted in the pitch itself, and, increasing in vigor as the border is approached, becomes upon the land a tropical jungle of canna and palms, perhaps thirty feet in height. In the center is a circle of islands that float on the pitch. The irregular water areas are many feet in depth, with nearly perpendicular sides, containing very transparent water that apparently has its source in subterranean springs. The areas of pitch arc of considerable extent, highest in the middle, but still nearly level and gently sloping on all sides to the precipitous edges of the water areas. These areas are being continually elevated in the center by rising gas, which, forcing up the center in huge bubbles, cause a continual ebullition of the plastic mass and a gradual transference of the material from the center towards the circumference, so that trunks and branches of trees submerged in the pitch come to the surface, rise, and after assuming a perpendicular position, are in time again submerged to an unknown depth. From the escaping gas the whole central portion of the lake is maintained in a constant motion that prevents vegetation
from taking root, and leaves the surface of the areas of pitch bare and of a blue-black color.
When the pitch is dug, a negro will drive a long, slender pick to the eye at a single blow, and, by using the handle as a lever, will break out a flake of pitch larger than he can lift. From less than an inch below the surface the pitch is of a brown color, saturated with water and filled with bubbles of gas. A broken mass will soon dry on the surface and melt, forming a pellicle that will enclose the wet mass for years and prevent the escape of the water. In this wet and porous condition it is called 'cheese pitch.' It is not sticky at all, as the water can be squeezed from it in the hand, as if it were a sponge.
Formerly the large lumps of this cheese pitch, as it was broken out, were transported to the beach in carts, but about 1893-4 a wharf was constructed on the Bay of Paria, near the lake, and a trolley line and tramway, leading from the wharf up to and out upon the lake in a loop, by which the pitch since then has been transported direct from the surface of the lake to the vessel being loaded. Formerly the pitch was carried from the beach to ships lying in the bay in lighters, the shipping entailing a great deal of labor from repeated handling. Since the tramway was installed, the pitch is dug along the line of the tramway and thrown into iron buckets, resting on trucks that are propelled along the tramway by an endless cable. Great difficulty was encountered when the tramway was laid to prevent its sinking in the pitch, which, while hard enough on the surface to bear up a loaded team, will slowly engulf any
article of even moderate weight. This trouble was overcome by laying the tramway on a bed of the leaves of the Moriche palm, some of which are twenty-five feet in length. When the car-buckets are loaded they are run to the power-house in groups of three or four, where, after being weighed, they are transferred by an ingenious device from the trucks to a trolley that runs on an endless rope from the lake to the wharf, where the contents of the buckets are dumped into the hold of the ship-like coal. The plant will handle 500 tons a day in the manner described.
Immense quantities of the pitch lie outside the lake, and the pitch from these deposits, wherever worked, is still shipped by means of lighters. The surface of the lake is 148 feet above the sea-level, and the pitch has flowed down to the sea from the lake in an immense stream that resembles a black glacier. Excavations made in this mass soon fill up again and all traces of them are in time obliterated, and buildings, the foundations of which are placed in or upon the pitch, are soon thrown out of perpendicular, from the unstable condition of the pitch, which appears to be moving or flowing towards the sea under a great pressure. These phenomena present the unique spectacle of a mass so solid as to be walked or driven over, and at the same time so plastic as to be in a state of unstable equilibrium, with constant ebullition from escape of gas and also in constant motion towards the sea.
Before the pitch is put to any use it is refined. In the operations attending its shipment and subsequent removal from the hold of the
ship, it has been very much broken up, and much of the gas has escaped with some of the water. In this condition it is put into enormous kettles, which are heated from above downward, and very slowly, until the contents of thirty tons or more are melted. The heat necessary to melt the pitch expels the water, the fragments of wood and other light impurities rise to the surface, and the heavy mineral matter, in large part, sinks to the bottom. The clean pitch between them is drawn off into barrels.
A more primitive method of refining the pitch is used at the island, where the pitch is boiled in old sugar kettles and skimmed, when the 'dean pitch is ladled into barrels and enters commerce as 'épurée.'
In the neighborhood of Trinidad, on the mainland of Venezuela, is another so-called Bermudez lake. It is found in a low savannah, extending between a range of mountains and the shore o tone of the estuaries that enter the northern part of the delta of the Orinoco from the Bay of Paria. The lake has an irregularly shaped surface, about one mile and a half by one mile in dimensions, giving an area of something less than 1,000 acres. This area is covered with rank grass and shrubs, from one to eight feet in height, with groves of large Moriche palms. There is no extended surface of clean pitch as at Trinidad; but instead, at certain points, soft pitch wells up as if from subterranean springs. As the general surface of the deposit is not more than two feet above the surrounding swamp, in the rainy season it is flooded, and at other times so low that any excavation will immediately fill with water.
Instead of being more than a hundred feet in depth as at Trinidad, this deposit is a shallow exudation from numerous springs, over a wide surface, from a mere coating to from seven to nine feet in depth, the average being perhaps four feet. The largest of the areas covered with soft pitch is not more than seven acres in extent. The soft material has become hardened in the sun at the edges, but at the center is too soft to walk upon, in this respect resembling many of the deposits of less extent in California. This pitch is also too soft to hold permanently the escaping gas, as at Trinidad, but when covered with water it ri>es in mushroom-like forms.
Some of these areas have been burned over, producing from the combustion of the vegetation and of the asphaltum itself an intense heat that has converted the bitumen into coke and glance pitch. When this crust of hardened material is removed, beneath it is found asphaltum that may be used for paving.
Under the classification that I have adopted, the bitumen of the Bermudez deposit is nearly pure asphaltum, which has been formed by. the heat of the sun and by fire, from an exudation of maltha, or mineral tar, over a wide expanse, beneath the coke and other products of combustion, while here and there are masses of glance pitch, which are the result of less violent action of heat.
Many of the West India islands, from Trinidad around to Cuba, contain deposits of asphaltum. The most noted among them are the Mumjack of Barbadoes and the asphaltum veins of Cuba. These, however, have not entered commerce, with the exception, perhaps, of the very pure asphaltum found in Cardenas harbor, which is obtained in limited quantities and is used in varnish-making. None of these are used in paving.
In Mexico there are very extensive deposits of asphaltum of great purity, but up to the present time they have not entered commerce.
In Texas, and extending into the Indian Territory, there axe large deposits of both siliceous and calcareous asphaltes. In Uralde county, Texas, near Cline, to the west of San Antonio, on the Southern Pacific Railroad, are very extensive deposits of coquina or shell limestone, filled with bitumen. As found, the material is very tough and difficult to break. When the bitumen is dissolved out with chloroform, there remains a mass of small shells, very light and porous, but with sufficient stability to form a rock. The shells contain from nine to thirteen per cent, of bitumen. While a large sum has been expended on a plant for extracting this bitumen, the enterprise has never proved a pecuniary success. In northern Texas, near the Red River, are extensive deposits of bituminous sand, which has been used locally for sidewalks with success. Across the Red River, near the Arbuckle Mountains, in the Chickasaw Nation, beds of bituminous sand occur of great extent. They extend across the country in anticlinal folds for miles in length. The material is not stone, as the sand falls into a powder as soon as the
bitumen is removed from it. When the material is broken into small pieces and placed in boiling water, the bitumen rises to the surface nearly free from sand, while the bulk of the sand sinks through the water clean. The bitumen thus obtained is of very superior quality for any purpose. Still farther north and east, near the town of Dougherty, several deposits occur. One is a mass of great extent of fragments of chert and limestone cemented together with bitumen. A mastic has been made by grinding this material. Another mass consists of a magnesian chalk, of carboniferous age, saturated with bitumen. Another is a mass of large shells filled with more than twenty per cent, of bitumen. Other deposits of loose sand occur in beds, saturated with ten per cent, of bitumen. These materials have been used separately and ground together for paving mixtures for street surfaces.
In Utah, upon the Uintah Indian reservation, are found veins of asphaltum of remarkable purity, to which the name 'Gilsonite' has been given. It has been found very useful for insulation and a great variety of purposes, but has only been used in combination with softer material for paving.
Among the coast ranges of California there are deposits of asphaltum and siliceous asphalte of vast extent. At Santa Cruz, to the east and west of Santa Barbara, near the coast near San Buena Ventura and Los Angeles, on the Ojai ranch, and at Asphalto, in Kern County, the principal ones are found. Those of commercial value are at the works of the Alcatraz Company, west of Santa Barbara, and near Asphalto. At the works of the Alcatraz Company the bitumen is dissolved in a
solvent and conveyed through pipes some thirty miles to the coast, where the solvent is removed and the bitumen prepared for shipment.
At Asphalto, on the north side of the Coast range, in Kern County, the asphaltum occurs nearly pure in veins of great extent that have been mined to a depth of more than three hundred feet. From these statements it will be seen that the deposits of asphaltum and asphalte in the United States are of vast extent and variety.
While the bitumen in these different deposits in different parts of the world bears a generic relation, there are specific differences between the different varieties that render some of them more desirable for certain purposes than the others. The purest asphaltums are brilliant black, brittle solids that consist of compounds of carbon and hydrogen with small proportions of oxygen, sulphur and nitrogen. The latter of these constituents are not always present and vary widely in amount when present, so that, from a chemical standpoint, the different asphaltums and the bitumens of the different asphaltes are very unlike substances. In the practical uses to which these substances are applied, the selection for any given purpose does not appear to depend upon difference of composition. The purest varieties are used for making fine varnishes and lacquers. Others are used for coarser varnishes that are baked on to iron and other surfaces. Others are applied, softened with solvents that evaporate. These substances find wide uses for insulating purposes, alone and in mixture with other materials.
The widest use to which they are applied is in street-paving surfaces, for which purpose vast quantities are used every year. It has been
found in practice that good streets and poor streets have been made from nearly all the different varieties of asphaltums and asphaltes that can be obtained in such quantity and at such a price as to render their use possible. The different results obtained appear to be due to causes external to the asphaltum or asphalte employed, such as the kind and quality of the materials with which they are mixed and the method, or lack of method, by which they are mixed. These conclusions appear to be warranted by a large number of experiments extending over many years, some of which have been very expensive for the municipalities making them.