BITU′MEN

[Eng., L.] Syn. Bitume , Fr.; Erdpech , Erdtheer , ., Ger. A term of a very comprehensive character, and, in general, very loosely applied, including a variety of inflammable mineral substances, consisting of varying proportions of hydrocarbons, having a strong smell and differing in consistence, all the varieties being found in the earth, of which asphaltum, naphtha, and petroleum may be mentioned as examples. Asphalt is very extensively di eminated throughout Europe, Asia, and America. Considerable quantities are exported from the West Indian Islands, and from the Dead Sea, in Judæa; hence its commercial name, ‘Jewish bitumen,’ or ‘Jew’s pitch.’ The different kinds vary greatly in quality, according to the amount of earthy matter and other impurities contained in them; they may all, however, be reduced to a state of equal purity by boiling or macerating them in hot water, by which means the earthy and siliceous matters are more or le completely removed. These latter fall to the bottom of the ve el, and the bitumen rises to the surface, or forms clots on the sides of the boiler, when it is skimmed off, and thrown into a large cooler, where more water separates. At the Sey el and Bechelbronn bitumen works the bitumen so obtained is thrown into large cauldrons and boiled for some time, by which means the volatile products and water accompanying it are driven off, and the remaining sand and impurities fall to the bottom of the cauldron, leaving the purified asphalt in the form of a thick fatty pitch, in which state it comes into the market or is applied to various purposes. In the following table we give the composition of a few bitumens: | Carbon, per cent. | Hydrogen, per cent. | Oxygen, per cent. | Nitrogen per cent. | | Viscous bitumen of Bechelbronn | 88·0 | 12·0 | — | — | | Virgin bitumen of Bechelbronn | 88·0 | 11·0 | — | 1·0 | | Liquid bitumen from Hatten, Lower Rhine | 88·0 | 11·6 | — | 0·4 | | Solid bitumen of Coxatambo, near Cuença, in Peru | 88·7 | 9·7 | 1·6 | Annexed is a table of the analysis of several asphalts, centesimally represented :— | Bitumen of Bastennes. | Bitumen of Pont de Chateau, Auvergne. | Bitumen of Abruzzi. | Bitumen of Mon as tier, Haute Loire. | | Crude. | Pure. | Crude. | Pure. | | Oily matters, Bitumen | 20·0 | — | — | — | — | 7·0 | | Carbon, Bitumen | 3·7 | 76·13 | 77·5 | 77·64 | 81·8 | 3·5 | | Hydrogen | — | 9·41 | 9·6 | 7·86 | 8·4 | — | | Nitrogen | — | 12·66 | 12·4 | 1·02 | 1·0 | — | | Oxygen | — | 0·5 | 8·35 | 8·8 | — | | Water | — | — | — | — | — | 4·5 | | Gas and vapour | — | — | — | — | — | 4·0 | | Quartz sand and mica | 76·3 | — | — | — | — | 60·0 | | Clay | — | — | — | — | Ferrug. 21·0 | | Ashes | — | 1·80 | — | 5·13 | — | — | | ——— | ——— | ——— | ——— | ——— | ——— | | 100·0 | 100·0 | 100·0 | 100·0 | 100·0 | 100·0 | The solid bitumens are now extensively employed in the manufacture of bituminous mastic or cement and similar compositions, which are used for the lining of water-cisterns, and for various other hydraulic purposes; as also for roofs, floors, roads, pavements, . For the last purpose the native varieties of ‘asphaltic rock,’ consisting of a mixture of bitumen and calcareous earth, when tempered with a proper quantity of crushed granite, or calcareous sand or gravel, is found to be the most substantial and durable. The plan followed in laying down such pavements in Paris, where they have been the most extensively adopted, is—The ground having been made uniformly smooth, is edged, in the usual manner, with curb-stones rising about 4 inches above its level, and then covered, to the depth of 3 inches, with concrete (made with about 1-6th part of good hydraulic lime), which is well pre ed upon its bed, the surface being subsequently smoothed over with a very thin coating of hydraulic mortar. On this, when perfectly dry, [187] the ‘bituminous mastic,’ rendered semi-fluid by being cautiously heated in a suitable iron cauldron, [188] is evenly spread over so as to form a layer three quarters of an inch, or for le solid work, half an inch thick. Some coarse sand is lastly sifted over and pre ed down on the surface, when the work is complete; and in a few days the pavement becomes sufficiently compact and solid to be thrown open to foot pa engers. [187] On this point depends the succe of the work. Absolute dryne is a sine quâ non in the proce . The mastic must also be laid down in dry weather. If laid in wet, damp, or even foggy weather, it will be liable to separate from its bed, and gradually to break up. This is why so much of the asphalt and bituminous pavement laid down in London has proved a failure. [188] It is here that the mixture of the bitumen (previously crushed sufficiently small to pa through meshes 10 to the inch) is made with the sand or gravel; a small portion of mineral tar or coal-tar (3 to 7 or 8%) being commonly added to promote their fusion and complete union. An important precaution to be observed in making asphalt pavements or roads is to boil the bitumen which is employed thoroughly, so as to expel the water and volatile oils, which if allowed to remain are found to render the mastic more liable to be affected by the extremes of heat and cold, as well as le able to stand the wear and tear of traffic. Claridge’s Proce . This consists in fusing the blocks of mastic in a suitable boiler, similar to that seen in fig. 1, and in adding a quantity of mineral tar, in the proportion of 1 lb. to every cwt. of the mastic. The tar is first fused in the boiler, 56 lbs. of the mastic are then introduced, and the whole repeatedly stirred so as to prevent the formation of a deposit. When the contents of the boiler are melted, the cauldron is covered over for a quarter of an hour, after which the remainder of the mastic is added, and its fusion proceeded with as before, the proce being repeated until the boiler is full, allowing an interval of from ten to fifteen minutes between each operation. When the mastic is sufficiently fluid it will drop freely from the stirrer, and jets of light smoke are observed to i ue from it. If stiff mastic be required, the proportion of tar is le ened, and a quantity of coarse grit or river sand, to the amount of 20 or 30 lbs. to the cwt. , is added. IMG:596405606043057898_i314-1.png: 1. In laying the asphalt the greatest attention and care must be paid to the preparation of a solid and dry foundation. This is usually accomplished by removing or ramming the loose earth, and placing upon the bed a layer of coarse sand mixed with powdered limestone, in the proportion of seven parts of the former to one of the latter, and the whole is pre ed or beaten solid; upon this a second layer of finer materials is laid compacted and levelled; the bed thus prepared is allowed to dry before coating it with mastic. Fig. 2 shows the manner in which ordinary asphalting is laid down. In this figure C is the bed of coarse concrete, B the second and finer layer of the same material, and A the superior layer of asphalt. IMG:596405606043057898_i314-2.png: 2. The base or concrete must be perfectly dry when the mastic is poured on, or the work will be a failure, for the moisture will be converted into steam, which, i uing through the fluid mastic, will cause the formation of holes in the latter or blister it, and ultimately the surface will crack. To counteract in some measure the evil arising from the formation of steam, fine cinder dust is sifted over the bed of concrete previous to the application of the mastic. When asphalting suspension bridges, a sheet of canvas is usually spread over the concrete. In asphalting damp places, such as cellars and foundations, a brick invert is always laid in asphalt beneath the concrete. This is done by placing the bricks in rows, at the proper depth and slope, and pouring a coating of asphalt about a quarter of an inch thick upon them. Before the mastic solidifies, the bricks are separated a little by pa ing a knife between them, thus affording the mastic an opening by which to seal up more thoroughly the connection. The concrete is afterwards laid upon this bed, and the layer of mastic upon this in the usual way. The thickne of the layer of mastic varies according to the attrition to which it is to be subjected; but the usual depth is from a quarter to one and a quarter inch. Artificial Asphalt. This is prepared from coal tar by distilling off the volatile oils which hold the tar in solution, the result being that a kind of fatty pitch is left, which must be boiled until a sample, when cooled, becomes nearly solid. The operation may be accomplished in the open air, but if this means of evaporation be adopted, the proce is attended with a very unpleasant odour, and the volatile oils are di ipated. These volatile oils are used for the preparation of varnish, for lubricating machinery, and for the manufacture of a superior kind of lampblack. They have also been employed to increase the illuminating power of coal-gas, which purpose they accomplish by imparting their vapours to gas pa ed over them when they are placed in shallow ve els. Various forms of patent apparatus have been designed for this purpose. When it is required to collect the oils, the coal tar is placed in a retort made of sheet iron, with a convex bottom, which is placed immediately over a fire. The products of the combustion after striking the bottom of the retort circulate round it, then proceed under a second boiler to heat the tar contained in it, and from which the retort is replenished when nece ary. This ve el, when three quarters full, contains nearly 24 cwts. of tar; it should be perfectly embedded in masonry; the capital itself by which the volatile products escape should be surrounded with materials that are bad conductors of heat, such as ashes. But for this precaution the volatile oils would become condensed, and fall back into the evaporating ve el. The volatile oils are collected by being made to pa through a tube cooled by a current of water, this tube running in a direction the reverse of that pursued by the vapours, and terminating in a closed ve el, which acts as the receptacle for the oils. A tube branching from the boiler conducts the uncondensed products outside the building in which the distillation is conducted. When the tar has been boiled sufficiently long to give it the requisite consistence, it is removed by means of a pipe into a third hemispherical boiler of cast-iron. To prepare the bituminous mastic directly from this fatty pitch, the latter is kept in a state of fusion, and chalk in sufficient quantity is then added. If the chalk be previously heated, ground to a coarse powder, and sifted, the mixture is effected more rapidly and satisfactorily. The asphalt becomes the more solid the greater the proportion of chalk added; on the other hand, it becomes le elastic and more brittle. The asphalt is moulded as follows:—A long table is covered with cast-iron plates, surrounded with a framework, which is subdivided into eight or ten equal compartments by means of rules of about six inches in height, introduced vertically into grooves formed at equal intervals in the long sides of the frame. The eight or ten moulds obtained by this means are coated internally with a paste composed of sixty parts of water and forty of chalk. This compound prevents the mastic adhering to the sides of the mould, and ensures its being easily detached. Two barrels, or 9 cwts. of tar, lose by distillation one fourth of their weight, the lo consisting of 1 cwt. 3 qrs. 15 lbs. of volatile oils, and 1 qr. 13 lbs. of water. Sometimes ground or fine sand enters into the composition of asphalt in proportions equal to the chalk; but in some cases only half as much sand as chalk is used. In the manufacture of asphalt it is very important that the contents of the cauldron should be stirred during fusion, not only to prevent the tar adhering to the bottom, and so getting burnt, but to ensure the ingredients being brought into intimate combination, and a homogeneous and smooth compound being produced. As soon as the whole is thoroughly incorporated, the proper consistence attained, and the vapours of the volatile oils and water come off in very minute quantities, the asphalt is run off into the moulds before described, and when sufficiently set may be removed, and is ready for use. Dr G. H. Smith has patented a proce for making artificial asphalt, waterproof concrete, ., which promises to become of great value in the construction of sea walls, docks, and harbour works, . Dr Smith’s invention consists in filling up the interstices of any porous substance, such as brick, burned or unburned clay, soft stones, plaster of Paris, ., with pitch or tar which has been boiled to such a consistence that the pores or cells of the material used are completely filled with solid matter when cold. Other hydrocarbons, resins, or gums may be used instead of pitch or tar; but it is e ential that the saturating substances, though naturally fluid or semifluid, can be so changed by boiling that they lose their fluidity when cold; or they must be, though hard under all ordinary temperatures of the atmosphere, capable of reduction by heat or otherwise to a fluid condition, so that they will penetrate the porous materials. The asphalto-bitumen mine of the Val de Travers, in the Canton of Neufchâtel, is said to be the richest and most extensive in the world of its particular cla . The calcareous bitumen which it yields contains 20% of nearly pure bitumen, and 80% of carbonate of lime; and it has a sp. gr. (2·115) approaching that of ordinary bricks. The ‘Val de Travers Company,’ and the ‘Bastenne and Gaujac Company,’ are, it is said, those which have hitherto been the most succe ful in laying down asphalto-pavements. See Asphaltum , Petroleum , .