Coal tar

“ While the electrician is pushing forward with rapid strides, the chemist is also moving onwards, and every year witnesses the discovery of new tar products, or the utilization of constituents which were formerly of little or no value. Thus if the cost of generating and distributing electricity is being lowered, on the other hand the value of coal tar is likely to go on advancing, and it would be rash to predict which will come out triumphant in the end. ”

“ The apparatus for the production of carburetted hydrogen from coal tar, is moreover less bulky, less expensive, and less complicated; and it can be managed by fewer workmen. And as the combined result of these several advantages, it is obvious, that by the substitution of coal tar, the new mode of lighting by gas can be pursued on a smaller scale; which it can never be with any profit, where coal itself is immediately employed for the production of the gas. ”

“ An improved process has been introduced by Martin and Grafton for the preparation of lamp-black from coal-tar, which affords a very good product. The coal-tar is first stirred up energetically with lime-water in any convenient vessel, after which the mixture is allowed to stand until the coal-tar has subsided to the bottom, when the lime-water is drawn off. The tar is then well washed by decantation with hot water, and rectified in the ordinary naphtha still. Afterwards it is run into a long iron cylinder, which is placed over a furnace, and supplied with numerous large burners. ”

“ The foundation of the coal-tar [Pg 47] industry was laid in this country—the country where coal was first distilled on a large scale for the production of gas, and where the first of the coal-tar colouring-matters was sent forth into commerce. We are at the present time the largest tar producers in Europe; it has been stated that we produce more than double the whole quantity of tar made in the gas-using countries of Europe ”

“ A consideration of these titles alone shows how vital the coal tar industry is. The coal tar as it comes to us as a by-product is distilled, giving off at different temperatures a series of compounds called crudes. ”

“ Coal gas, as it leaves the retort, has many impurities. It is accompanied with about 3 its weight of coal tar, 1/2 its weight of H2O vapor, 1/50 NH3, 1/20 CO2, 1/20 to 1/50 H2S, 1/300 to 1/600 S in other forms. The tar is mostly taken out at the hydraulic main, which also withdraws some H2O with other impurities in solution. The condensers remove the rest of the tar, and the H2O, except what is necessary to saturate the gas. At the main, the condensers, and the washers, NH3 is abstracted, CO2 and H2S are much reduced, and the other S compounds are diminished. ”

“ At one time regarded by gas engineers as unfortunately necessary nuisances in the manufacture of gas, they have both become so valuable on account of materials which can be obtained from them, that they enable gas itself to be sold now at less than half its original price. The waste of former generations is being utilised in this, and an instance is recorded in which tar, which was known to have been lying useless at the bottom of a canal for years, has been purchased by a gas engineer for distilling purposes. It has been estimated that about 590,000 tons of coal-tar are distilled annually. ”

“ New processes were invented by which valuable gas and coal tar are taken out of bituminous coal, leaving, as a residue, coke that is equal in quality to that made from the Connellsville coal. Fortunes have been made out of the separation of the elements of the once despised soft coal. For the coke and each of its by-products, coal tar and coal gas, are commercial necessities of life. [Pg 173]
The impurities absorbed by the melting iron ore include carbon, phosphorus, and silicon. Carbon is the chief cause of the brittleness of cast iron. ”

“ PART XVI. Other products obtainable from Coal, namely:—Coal Tar—Pitch—Coal Oil—Ammoniacal Liquor, and conversion of the latter into Carbonate, and Muriate of Ammonia. Coal Tar. The coal tar is so called from its resembling common tar in its appearance, and most of its qualities.
This substance is deposited in the purification of the coal gas, in a separate vessel destined to receive it. See fig. ”

“ This process has been adversely criticized by very competent gas-makers, and no great success can be expected in this line.
Coal-tar is very much employed for painting wood, iron, brickwork, or stone, as a preventive against the influence of weather or the far more potent action of corrosive chemicals. This, of course, can be done only where appearance is no object, for instance in chemical works, where all kinds of erections and apparatus are protected by this cheap kind of paint. ”

“ This peculiarity of the solid, resinous constituents of the coal tar, to be by the operation of the atmospheric oxygen altered into such products that are readily soluble in water, makes the tar very unsuitable as a saturative substance for a roofing paper. ”

“ The various proprietary coatings are mainly coal tar pitches, or mixtures of coal tar pitch and asphalt. A coal tar pitch is a distillate of coal tar from which the naphtha has been removed and to which about one per cent of heavy linseed oil has been added. ”

“ The total number of coal-tar products runs into the thousands, and is constantly being increased by fresh discoveries.
In Germany, just before the war, the industries engaged in making these products (no longer by-products, but far more important than coke and gas) were capitalized at $750,000,000. One firm made no less than 1,800 coal-tar dyes, besides 120 pharmaceutical and photographic preparations. ”

“ Ten per cent of the coal should be cannel; naphtha is, however, often employed to subserve the same purpose, one ton of ordinary bituminous coal requiring four gallons of oil.
In Boston, 7,000,000 cubic feet of gas have been burned in one day, consuming 500 tons of coal; the average is not more than half that quantity. Of the other products, coke is employed for heating purposes, gas carbon is used to some extent in electrical work, and coal-tar is the source of very many artificial products that were formerly only of natural origin. ”

“ Aside from its use as fuel, upon which civilization is dependent, coal is a source of an endless variety of valuable products. It is the source of our illuminating gas, and ammonia is one of the products of the gas manufacture. From the coal also comes coal tar, the material from which such a long series of valuable materials, as aniline colours, carbolic acid, etc, is derived. The list of products which we owe to coal is very long, and the value of this material is hardly to be overrated. In the preparation of these ingredients from coal bacteria do not play any part. ”

“ It may be generally said that for the purpose of tar-distillers the tar is all the more valuable the less other materials than real coal have been used by the gas-maker. All these materials—bog-head shale, bituminous lignite and so forth—by destructive distillation yield more or less paraffinoid oils, which render the purification of the benzols very difficult and sometimes nearly impossible for the purposes of the manufacturer of coal-tar colours.
Neither too high nor too low a temperature should have been observed in gas-making in order to obtain a good quality of tar. ”

“ If the coal tar is wanted to be converted into pitch, without obtaining the oil which it is capable of furnishing, the evaporation of it may be performed in a common boiler; but as it is extremely liable to boil over, the greatest precaution is necessary in conducting the evaporation. A spout or rim is added to the common boiler into which the tar spreads itself as it rises, and by this means becomes cooled, and the boiling over is checked. ”

“ Coal-tar, a waste product of gas-works, can be applied with an ordinary painter's brush, and may be used cold, except in very cold weather, when it should be slightly warmed before application. Coal-tar has remarkable preservative properties, and may be used with equal advantage on living and dead wood. A single application, without penetrating deeper than ordinary paint, forms an impervious coating to the wood-cells, which would, without such covering, under external influences, soon become channels of decay. ”

“ If we have more coke than we ourselves need it is sold for fuel. The coal-tar goes for roofing and making sidewalks, or sometimes (though you wouldn’t think it possible, as you look at the sticky, bad-smelling, black stuff) in the manufacture of the most lovely dyes, like that which colored Miss Kitty’s pink ribbon. The ammonia is used for medicine and all sorts of scientific preparations, in bleaching cloth, and in the printing of calicoes and cambrics.”
“When the materials of the coal are separated as I told you in the retorts, most of the tar remains behind, and is drawn off ”

“ The coal we employed was what is known as Stravenhouse small coal, which costs 5s. per ton delivered. The experiment in each case lasted 48 hours. The tar employed was what is known as boiled tar; the naphtha having been previously removed, but the pitch oil left in the tar. The value of this tar in Dundee is about 4s. per ton. The following are the figures:
And this at the longest day, when we are using a mere fraction of steam, as compared with our winter requirements, and consequently the profit is proportionally less than it will be when we are in full work. ”

“ The Young Chemists' Club still continues to be a success. At a recent meeting, Professor S—— was present, and gave us a very instructive lecture upon the products of coal-tar, of which I give a brief abstract to the readers of Our Post-office Box: The most wonderful product, from the manufacture of coal-gas is coal-tar—a most unpromising-looking substance, but containing much of interest and value. By distilling coal-tar we get many more new products. ”

“ Of the by-products of gas-making, ammoniacal liquor was, until recently, the only commercial source of ammonia. Coal-tar, formerly thrown away as worthless, is today the source of innumerable substances of immense value to science and the industries. ”

“ 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. ”

“ C6H5OH, besides another interesting oxygenized substance, cumarone C8H6O. The phenols, especially the carbolic acid, are among the more valuable constituents of coal-tar. Numerous sulphur compounds also occur in coal-tar, some of which impart to it their peculiar nauseous smell, but they are of no technical importance or value.
Still more numerous are the nitrogenated compounds contained in coal-tar. Most of these are of a basic character, and belong to the pyridine and the quinoline series. ”

“ Electric power generation consumes the greater part of the annual coal production in Illinois. Coal is also used for home and commercial heating, for production of coke, and for manufacturing various chemical compounds from coal tar. Products derived from coal tar include drugs and medicines, plastics, synthetic fibres, perfumes, flavorings, dyes, synthetic rubbers, explosives, specialized oils, solvents, wood preservatives, tarlike paving and roofing materials, and some gas. ”

“ If bituminous coal, it contains also a certain amount of hydrogen, which in combination with carbon enables it to yield gas and coal tar, and which causes it to burn with flame. If, again, we examine some of the more imperfect and more recent coals, the brown coals, so called, we shall find that in composition and texture they are intermediate between coal proper and hardened or compressed peat. ”

“ Thus, the whole art of tar-making is no other, than a kind of rude distillation per descensum, and might therefore be as well done in furnaces of large capacity, were it worth the expence. When the tar is now all melted out, and run, they stop up all the vents very close; and afterwards find the knots made into excellent charcoal, preferr’d by the smiths before any other whatsoever, which is made of wood; and nothing so apt to burn out when their blast ceaseth; neither do they sparkle in the fire, as many other sorts of coal do ”

“ The removal of the tar and ash from a gas is called SCRUBBING, and is performed by a device much resembling a filter. Anthracite coal and coke are low in volatiles or hydrocarbons, and therefore do not cause trouble with tar deposits. ”

“ It is a long distance from any tar distiller's works capable of dealing with the large quantity of tar we have for sale during the winter. A large portion of the value of our tar must, therefore, go to the railway company, to cover the cost of transit between the two points, and so the tar distiller can allow us but a small figure for it at the starting point. Then again, Dundee being far distant from the coal fields, the coal is exceptionally high in price. I quite believe that in many of the west country towns the coal for which we are paying 5s. per ton could be had for 3s. ”

“ The final solution of the question of enrichment of gas by hydrocarbons derived from tar may be arrived at by a process which prevents the formation of part of the tar during the carbonization of the coal, or by the process devised by C.B. Tully and now in use at Truro, in which tar is injected into the incandescent fuel in a water-gas generator and enriches the water gas with methane and other hydrocarbons, the resulting pitch and carbon being filtered off by the column of coke through which the gas passes. ”