Coal Products. The readiness shown by the elements of coal to enter into new combinations where it is exposed to an increase of temperature, and the great variety of the combinations obtained under different degrees of heat, or by the admission or exclusion of air, indicate the close relation of coal to the elements of the vegetable kingdom. It consists of carbon, hydrogen, oxygen, and nitrogen, which make up the great bulk of vegetable matters, and these show the same disposition as in the plants themselves to separate from existing combinations and enter into new. The number of the new products thus formed is almost unlimited. They differ from one another, and from the original substance from which they are generated, as do those obtained in the processes of vegetable fermentation. When heat is applied without access of air, the vapor of water set free acts upon the existing combinations of the elements. These are broken up, and hydrogen and oxygen are evolved under the most favorable circumstances, in their nascent state, to form new compounds with the carbon present, the characters of which vary greatly with the temperature. The process is called dry distillation.
By keeping the retorts in which it is conducted at a cherry-red heat, the gases used for illumination are most copiously evolved, the tar itself being decomposed and converted into gaseous matters. (See Gas.) But if the object is to obtain the coal oils, paraf-fine, benzole, and other hydrocarbons of this nature, care is taken that the retorts are heated very gradually, and do not acquire more than a low red heat. The tarry matters thus escape decomposition, and by repeated distillations afford crude naphtha and its secondary products. The foregoing table represents in the clearest manner the great variety of substances besides coke which are obtained by means of this process, and their immediate sources. - Coal tar was for a long time a troublesome product of the gas works, no useful application of it to any great extent being known. It was employed as a covering to protect iron work exposed to the weather; and the pitch obtained by distilling it was found when mixed with earthy matters to be a good substitute for the natural product asphaltum, used for artificial pavement, water-tight covering for roofs, etc. Finally the tar came to be an object of purchase by tar distillers, who learned to extract from it the crude naphtha and also the light oily fluids.
The pitch, too, by repeated distillations was made to yield more oily matters, which are useful for lubricating machinery and other purposes. The crude naphtha is now purified by mixing it with 1/10 its bulk of concentrated sulphuric acid, adding when cold 5 per cent, of peroxide of manganese and distilling off the upper portion. A rectified naphtha is thus obtained, which readily dissolves caoutchouc, and mixed with wood naphtha produces a powerful solvent of various resinous substances, useful in making varnishes. Still further purified, the liquid benzole is obtained, which has been applied to many useful purposes, especially that of an illuminating agent. The light essential oils, as also the heavier qualities which come over after these, are found to possess antiseptic properties, which render them of value for preserving wood from decay. From the essential oils the tar creosote or carbolic acid is obtained, which possesses extraordinary antiseptic properties, and is used in the preparation of a valuable dyestuff called carbazotic acid. The heavy oil yields a substance called aniline, which gives with bleaching powder and other agents a magnificent blue color, and is employed in dyeing.
Naphthaline also, which is a solid white substance obtained in large quantities in the distillation of the tar, yields two coloring matters, one called naphthalic acid, and the other chloronaph-thalic acid; the latter of which is nearly identical with the coloring principle of madder, and gives with alkalies a beautiful red color. Instead of naphthaline, by conducting the distillation at a lower temperature, may be obtained the waxy substance called parafline, which is now used for the manufacture of candles and the parafline oils. The most important of these products will be found more particularly noticed under their separate heads, and the general subject will receive further attention in treating of gas light. - By oxidizing aniline with bichromate of potash a bronze-colored substance is produced, dissolving in alcohol with a beautiful purple color. In concentrated sulphuric acid its solution is green. On adding water and precipitating with an alcoholic solution of potash, the coloring matter is precipitated unchanged.
It is of intense hue, and considered as good if not better than archil; it is very stable, not being decomposed at a temperature of 482° F. One pound of the solid substance will dye 200 lbs. of cotton a moderately dark lilac, the color standing well the action of light and heat, acids and alkalies. The distillation of coal for obtaining parafline and the oil accompanying has been conducted in the following manner: The retorts used are like those employed in making gas. A worm passes from them through a refrigerator kept at a temperature of about 55° F. The oil condenses in the worm, and is collected in a receiver. It deposits some parafline when cooled to a low degree. Some illuminating gas is generated in the process and escapes. Coke also remains in the retort, as in the gas-making process. The oil is purified by heating a cistern of it to about 150° F. Water and insoluble impurities subside on standing, and the oil may be drawn oft". It is redistilled to dryness, and a carbonaceous residuum is left in the iron still. From the cold condenser it is run into leaden vessels, and 1/10 its bulk of oil of vitriol is added and the mixture is well stirred for an hour. In 12 hours the sulphuric acid has settled, together with the impurities it has taken up.
The oil is then drawn off into an iron vessel, and 4 gallons of a solution of caustic soda, of sp. gr. 1.3, are added to every 100 gallons of oil. This is well stirred for an hour, to take up all the remaining acid, and it is then left for 6 or 8 hours for the soda and impurities to subside. The oil is again drawn off and distilled. Parafline oil thus obtained contains a more volatile oil, that may be mostly separated from it. Half its bulk of water is added to it, and the mixture is distilled as before, the boiling being continued for 12 hours by renewing the loss in the still with more water. The steam carries the more volatile fluid over with it. They condense in the worm, and separate by standing in the receivers. This fluid is suitable for burning in lamps and for other purposes. The oil left in the still is to be drawn away from the water left with it, purified by distilling from 1/50 its bulk of sulphuric acid, and then from chalk added as the caustic soda was used. The oil is kept for a week in a warm place, and being then drawn off from the sediment is fit for lubricating or illuminating purposes.
Cooled to 30° or 40° F., the parafline crystallizes, and may be collected by pressing out the oil through cloths. - An improvement made upon this process consists in introducing highly heated steam into the retorts with the bituminous matters. It rapidly unites with and carries off the volatile matters arising from the coal, checking their conversion into gas, and greatly increasing the amount of oily or condensable product. The condenser is kept at a temperature of about 55° F. The products obtained are next distilled, and very hot steam is introduced again, if much paraffine rather than oil is desired. At different stages of the process different products are obtained, which are separately collected. These are, first a thin, impure eupione oil, to the extent of about one eighth of the fluid; then a thicker and heavier oil, containing paraffine, amounting to two fifths or one half of the fluid; and lastly, paraffine mixed with heavy oil. The crude eupione oil is purified by adding 5 to 10 per cent, of sulphuric acid, diluted with an equal bulk of water, and half as much by weight of bichromate of potash as of the acid. Heat is then applied, and the mixture is well stirred while heating. When it has reached the temperature of 212° F. it is allowed to cool and settle.
The eupione, being drawn off, is next treated with a warm solution of caustic soda, and left to settle. It is at last taken off from the heavier fluid and distilled. The heavier oil is treated very much in the same way, the black oxide of manganese instead of the potash salt being sometimes used with the sulphuric acid. The first comings over in the distillation are added to the eupione oil; but the greater part is the so-called "lubricating oil," the most important product of the process. The last portions are thick like butter, and yield mostly paraffine when treated with that already obtained with the heavy oil. This, after being allowed to crystallize in a cool place, is put in a bag for the oil to drain away. It is then pressed, melted, and when cold pressed again, the oil being added to that already obtained. It is melted again, and at the temperature of about 400° F. from 5 to 10 per cent, its weight of strong sulphuric acid is stirred in. On boiling, the remaining oil is completely charred, and on cooling settles as a black powder. Another boiling after separating this powder completes the purifying process, though the paraffine is now after several new methods bleached to a beautiful degree of whiteness.
Its properties will be described in the article Paraffine. - Coal oils have been manufactured at several localities in the United States. Important works at Cloverport, in Breckenridge co., Ky., on the Ohio river, were destroyed by fire in 1858. They produced large quantities of an oil of excellent quality, which was on trial with a view to its being introduced into our lighthouses; but all the coal oil distilleries have been closed by the discovery and wonderful production of petroleum, which amounted to 539,472 barrels in the month of June, 1872, from the Pennsylvania oil regions alone. Not only the cannel coal and other fat coals produce these oils, but the bituminous shales, until of late years regarded as worthless, have been applied at Dartmoor, in the west of England, at Autun, France, and at Buhl in Prussia, to the same purpose.
TABLE REPRESENTING TILE PRODUCTS DERIVED FROM THE VOLATILE MATTERS OBTAINED IN THE
DISTILLATION OF COAL.
Liquids condensed and. collected in tar -cistern.
Coal tar gives, on redistillation with -water or steam,
Distilled tar; which affords, on further -distillation,
Pitch; distilled in ovens, affords
Dead, or pitch oil, consisting of
Naphthaline, paranaphthaline, and oily hydrocarbons boiling at a high temperature, creosote, aniline, leucoline. paraffine.
Crude coal tar naphtha, which consists of
Acids - Eosolic, carbolic, brunolic, creosote. Basis of the pyrole, picoline, aniline, leucoline, methylamine, ethylamine, and other series. Neutral: Alliole, benzole, toluole, cumole, cymole, and other carbohydrogens; naphthaline, hydrate of phenyle (Laurent).
Ammoniacal liquor, containing
Gases and vapors separated in lime purifier:
Gases and vapors.
Gases and vapors separated sometimes by additional chem-ical agents:
Gases and vapors conducted to gas-holder:
Vapors of hydrocarbons.
Light carburetted hydrogen,
Very small quantities -
Vapor of bisulphuret of carbon,