PARAFFIN. In the course of his classical investiga-tion on the tar produced in the dry distillation of wood, Reichenbach in 1830 discovered in it, amongst many other things, a colourless wax-like solid which he called paraffin (parum affinis) because he found it to be endowed with an extraordinary indifference towards all reagents. A few years later he isolated from the same material a liquid oil chemically similar to paraffin, to which he gave the name of eupion (evirCwv, very fat). For many years both these bodies were known only as chemical curiosities, and even scientific men looked upon them as things entirely mi generis; this was natural enough as far as paraffin is concerned, but it is rather singular that it took so long before it was realized that eupion or something very much like it forms the body of PETROLEUM (q.v.), which had been known, since the time of Herodotus at least, to well up abundantly from the bowels of the earth in certain places. Though extensively known, it was used only as an external medicinal agent, until the late Mr James Young conceived the idea of industrially working a com-paratively scanty oil-spring in Derbyshire, and subse-quently found that an oil similar to petroleum is obtained by the dry distillation of cannel coal and similar materials at low temperatures. This discovery developed into a grand industry, which may be said to have led to the utilization of those immense natural stores of petroleum in America. Scientific chemists naturally directed their attention to the products of these new industries, and it was soon ascertained that solid paraffin and eupion, as well as natural and artificial petroleum, are substantially more or less impure mixtures of saturated hydrocarbons; and so it comes that, on the proposal of H. Watts, the word paraffin in scientific chemistry has been adopted as a generic term for this class of compounds of carbon and hydrogen.
When the electric light is generated within an atmo-sphere of hydrogen, then, at the immense temperature of the electric arc, part of the carbon of the charcoal terminals unites with the hydrogen into acetylene gas, C2H2. Apart from this isolated fact, which was discovered by Berthelot in 1862, it might be said that the two elements are not capable of uniting directly, although an innumerable variety of hydrocarbons exist in nature, and can be pro-duced artificially from organic substances. Individual hydrocarbons may differ very .much in their properties. At ordinary temperature and pressure a few are gases; the majority present themselves as liquids ; not a few are solids. But the solids are fusible; and all liquid or liquefied hydrocarbons, at a high enough temperature, volatilize, as a rule without decomposition. To the latter circumstance to a great extent we owe our precise know-ledge of their chemical constitution.
In all the numerous series of hydrocarbons the percentages of carbon vary from 75 (in marsh gas) to 94'7 (in chrysene). Within this narrow range of some 20 per cent, several dozens of elementary compositions have to be accommodated; and many of these, to be represented in formula1, C^Hj with an adequate degree of precision, require formulae in which the coefficients x and y are so large that, by means of integers less than these, any fancy composition (within our limits) may be expressed with a degree of exactitude which is quite on a par with the analyses. But these hydrocarbons, in general, can be volatilized into gases, and in regard to these Avogadro's law tells us that quantities proportional to the mole-cular weights (i.e., the weights represented by the true chemical formula;) occupy the same volume. Hence, to find the true value, M = CJ;HJ, of the formula as a whole, we need only determine the vapour density, and from it calculate the weight of the respective hydrocarbon which, as a gas at f and P millimetres pressure, occupies the same volume as, for instance, H20 parts of steam. This is M. The elementary analysis enables us to calculate the weight x x C of carbon contained in M parts, and the analysis must be very poor to leave us ill doubt as to whether it is for instance 6x12 parts of carbon or 7x12 parts that we have to deal with. The reader will now understand how it has been possible to ascer-tain the elementary composition of all pure hydrocarbons with a degree of precision which goes beyond that of the analysis, and to prove what analysis could never have done by itself, namely, that there are numerous groups of hydrocarbons which have absolutely identical elementary compositions,—cases of isomerism, as they are called. We speak of isomerism in the narrower sense " when the atomic formulae are identical (there are, for instance, two hydrides of butyl, C4H]0), while we speak of " polymeric " bodies when the several formulae are integer multiples of the same primi-tive group {e.g., ethylene, 2xCH2, and butylene, 4 x CH2, are polymers to one another).
The following table gives an idea of the several classes of hydro-carbons which for us come more particularly into consideration.
== TABLE ==
The first column, under "«," gives the number of carbon atoms per molecule in the compounds whose formula; stand in that hori-zontal line,—these latter being arranged in a descending series according to the number of hydrogen atoms united with n atoms of carbon. Instead of pointing out those regularities, in regard to the atomic proportions in which carbon and hydrogen can unite into compounds, which the table illustrates so forcibly, let us rather state that the "benzols," in opposition to all that stands to their left in the table, are things of their own kind. In them six atoms of the carbon are most firmly united (into a " ring, "as » certain theory says), and the rest are, so to say, hooked on to the ring in a less intimate fashion. Thus benzol is (C6)H6; each one of the six H's being tied to one of the six C's ; toluol is (C6H6)—CH3; it is a benzol from which one of the six hydrogen atoms has been removed, and in which the gap left has been filled by a " methyl," CH3 :—
C6H6 + CH4 = H2 + (C6H5)-(CH3). Benzol. Marsh gas.
But similarly two dehydrogenated benzols, C6H6, can unite into one double ring of diphenyl: 2C?H6 - 2H = (C6H5)(C6H5); and two benzol rings may unite more firmly in such a manner that two carbon atoms of the one ring do service for the two rings, and a double ring is formed firmly united by these two common carbons, the four hydrogens of the original two benzols being away. This gives naphthalene :—
CBH6 + C6H0-2C-4H-C10H8.
Benzol. Naphthalene.
In a similar manner throe benzols may unite into one anth-racene :—
C6H6 + C6H6 + C6H6 - 4C-8H — C]4Hi0.
Benzol. i Anthracene.
Generally speaking, a hydrocarbon is the more volatile the less the number of carbon atoms and the greater the number of hydrogen atoms in the molecule. Thus, in the series of "paraffins," CH4 (marsh gas) and C2H6 (ethane) are gases, C3H8 (propane) and C4H10 (butane) are very volatile liquids, and C6H12, &c, are liquids,—with higher and higher boiling points as we ascend the series. From a certain value of n upwards we find ourselves amongst the paraffins proper, which are solids, more or less easily fusible, but not, in general, volatile without decomposition. Benzol, C6H6, and its neighbouring homologues are volatile liquids. Naphthalene and anthracene are crystalline solids, fusible at 79°'2 and 180° C, and boiling at 217° and above 300° C. respectively without decomposition.
All hydrocarbons agree in this, that they are practically insoluble in water, but more or less readily soluble (in general) in alcohol and in ether. They are all combustible ; the more readily volatile ones are inflammable. Any complete combustion, of course, leads to the formation of only carbonic acid and water, with evolution of a large amount of heat; but the mechanism of the process is more or less complex. Naphthalene and anthracene remain un-decomposed at a red heat; only at the very high tempera-ture of their flames, and by the co-operation of the oxygen of the air, they are decomposed with large elimination of charcoal; a similar, though less, stability is exhibited by the benzols. The paraffins, on the other hand, are relatively unstable. Marsh gas, it is true, stands a red heat ; but, to pass to the other end of the series, the paraffins proper, and also the higher liquid paraffins to some extent, even when being distilled, and especially when distilled " under pressure," i.e., at higher temperatures than their natural boiling points, break up into defines and lower paraffins (Thorpe and John Young). Similar changes take place when the vapours of paraffins are passed through red-hot tubes; only the products formed then suffer deeper-going decomposition with formation of hydrogen, marsh-gas, acetylene, ethylene, and charcoal, and, last not least, benzols and naphthalene. To this latter fact the paraffins owe their pre-eminent fitness as illuminating agents.
When organoid minerals, such as cannel coal, shale, &c, are subjected to dry distillation, all the several classes of hydrocarbons are in general produced at the same time; but, from what we have said it will be understood that, even with the same material, the quantitative composition of the complex vapour which comes out of the retort depends on the way in which the distillation is being conducted. If we operate at the lowest practicable temperature, comparatively little gas is produced, and in the condensible part of the vapour the paraffins pre-dominate largely; at a bright red heat, such as is used in making coal gas, and especially if the vapours have to pass along red-hot surfaces before they get into the condenser pipes, more gas is produced, and the place of the liquid paraffins is taken by benzols. These latter, however, are always accompanied by naphthalene, often also by anthra-cene, and invariably by certain ternary benzol-derivatives, namely, by "phenols," feebly acid bodies containing hydroxyl groups, OH's, where the corresponding hydro-carbon bore plain hydrogens (ordinary phenol, C6H6(01I), derived from benzol, C6H6H, is a representative example), and, secondly, basic compounds of carbon, hydrogen, and nitrogen. Of the latter aniline and picoline— both C6H7N, but widely different in their properties —may be quoted as examples. The gas produced in this case through the presence in it of the vapour of higher hydrides, but especially of acetylene, C2H2, and benzol is highly luminous. Supposing now, as a third instance, the distillation to be conducted at a white heat, and so that the primary vapour has to wind its way through a spiral pipe kept at a bright red heat, the pro-portion of gas increases largely, and there is an increased yield of retort charcoal; but the liquid hydrocarbons of all classes almost vanish; the gas consists mainly of hydrogen, marsh gas, carbonic oxide, and carbonic acid, and gives little light when kindled.
The aim of the paraffin oil manufacturer is to produce the best possible approximation to a mixture of paraffins, wherefore he conducts his distillation at the lowest work-ing temperature. Of course his paraffin mixture contains more or less of the other classes of bodies referred to, whose removal, however, offers no great difficulty. In the laboratory we should commence by shaking the crude oil with caustic alkali ley, which withdraws the phenols and other acid bodies, as part of a lower layer, the upper being purified oil. By shaking the latter with dilute sulphuric acid the bases are removed as a solution of their sulphates, and a still purer oil results. Application of con-centrated sulphuric acid to the latter removes part at least of the benzols and defines as sulpho-acids, and also of the phenols and all the bases, should the two preceding operations have been omitted. But the most thorough mode of getting quit of the benzols and their derivatives is —after having exhausted the milder agents—to shake the oil with first aqueous and then stronger and stronger nitric acid, which reagent converts the benzol-bodies into nitro-products, soluble in the acid, or removable, after separation of the acid layer, by aqueous alkali. By all these tortures the paraffins—being what the name implies—are not much affected, so that what ultimately survives all belongs to their family. The separation of the individual paraffins from one another is a very difficult problem which has not yet found a satisfactory solution. What we know of in-dividual paraffins is derived chiefly from the investigation of decompositions of pure chemical substances leading to the formation of that one paraffin principally if not solely. To split up a mixture of paraffins approximately the only known method is fractional distillation (see DISTILLATION, vol. vii. p. 260), preferably by means of an apparatus so constructed that the vapour, before reaching the con-denser, ascends through an intermediate inverted con-denser or still-head, and there suffers partial condensation at some suitable temperature (enforced in the most perfect form of the apparatus by an oil-bath surrounding the still-head). In this latter case, singularly—not as a matter of course by any means—what goes over boils very nearly at the temperature of the still-head. This particular form of the method therefore lends itself chiefly for the final purification of an unitary substance of known boiling point already purified by preceding distillations. With mixtures of unknown composition the process is very tedious, and may assume something like this form.
We distil the substance (slowly and with ample chance of partial condensation) and collect as separate fractions what came over at, for instance, 100° to 105°, 105° to 110°, 110° to 115°, &c, as I, II., III., IV., &c. Each of these when redistilled yields I. and II. and III. and IV., <fec, which parts are poured into the respective receptacles, and on this principle we continue working. If the sub-stance happens to be of comparatively simple composition, it usually turns out, after a while, that (say) the two fractions II. and VI. increase while the rest get less and less; and by working on we may be able to isolate two bodies of the constant boiling points and t6 respectively, with formation of " tails" of other boiling points. Unfortunately, even a constant boiling point is no proof of chemical purity; and, if a constant-boiling substance is a mixture, only chemical methods can help us out of the difficulty.
The following table (extracted from Roscoe and Schorlemmer's Handbook of Chemistry, German edition) gives the names, specific gravities, and boiling points of the more important paraffins. The first column, " n," gives the number of carbon-atoms in the molecule, and consequently the molecular weight M and the vapour density S. In the case of "pentan," for instance, we have n=5; hence M = C5H12 = 72; and, as H2 = 2, the gas-density, referred to hydrogen = S = 36, while, as air is 14'45 times as heavy as hydrogen, for the gas-density referred to air the value
Sp. Gr. of Liq. at t° C.
iM-f-14-45 = 36-=-14'45 = 2-491.
Fahr.
atmospheres' atmospheres
Boiling Point in Degrees.
Liquid at —11° C. and 180
pressure (Cailletet). Liquid at H-4° C. under 46
(Cailletet).
-13° to— 22° —25°to—30°
+34° +1°
+1° -17°
99° to 102° +37° to 39°
86° 30°
49° 9°-S
156° 69°
144° 62°
140° 60°
136° 58°
109° to 118° 43° to 48°
209° 98°-4
195° 90°-3
205° 96°
187° to 189° 86° to 87°
258° 125°-5
227° 108--5
221° to 223° 105° to 106°
Cent.
-Methan or marsh gas..
0-600
(?)
0-6263 0-6385
(?) 0-663 0-701
(?) 0-6769
(!) 0-7005 0-6969 0-689 0-7111 0-7188 0-7111
(?) 0-7279 0-7247
(?) 0-7394
(?) 0-7413
(?)
•Ethan or dimethyl
'Propan.
•Butan, normal
Isobutan or trimethylmethan, a gas
Pentan, normal
*Isopentan
Tetramethylmethan
_Hexan, normal
Tsohexan
Methyl-diethylmcthan
Tetramethylethan
Trhnethylethyimethan
*Heptan, normal
Isuhcptan
Triethylmethan
Diethyl-dimethylmethan
*Oetan, normal
Te'.ramethyl-butan
13
0°
147° to 148° 132° 130° 166° to 168° about 160° 160°
Not yet isolated. 202°
297° to 298'
270°
266° 331° to 334
320°
320°
396°
Hexmcthylethan, fuses at 96" )
to 97° /
13°-« "o
*Nonan, normal
Tetramethyl-pentan
Pontamethyl-butan
"Dekan [normal ?]
Dimethyl-heptylmethan
Tetramethyl-hexan or " diamyl "..
Hendekan
Dodekan, normal
1
_ Not isolated yet.
Hekdeka-dekan, normal, fuses at
+21° C
Probably all the paraffins enumerated in the table are present in paraffin oil and in petroleum; those marked * have been actually found in the one or the other. The solid paraffins are not known as unitary chemical substances ; no chemist as yet has succeeded in splitting up solid paraffin into its proximate components. The manufacturer, in regard to the liquid paraffins even, does not trouble him-self with the isolation of chemical species; he contents himself with splitting up his oil into fractions correspond-ing to certain ranges of boiling point, and consequently adapted to certain practical applications. But even the boiling point is not much heeded industrially; the several kinds of oil are defined by their specific gravity at 60° F., which, as experience shows,' increases as the boiling point rises. But it is as well here to point out that the same (initial) boiling point even, and in a much higher degree the same specific gravity, may be exhibited by oils of widely different proximate composition. Hence a relatively (and in a sense sufficiently) high specific gravity is no guarantee against dangerous inflammability; the degree of inflammability in an oil must be—and in practice always is being—determined by direct experiment. For this purpose it is not sufficient to heat a sample oil in an open vessel gradually to higher and higher temperatures, and to note the temperature at which the atmosphere over the oil proves inflammable when a lighted taper is brought in contact with it. By this method (which formerly was the universally recognized test) the most varying results may be obtained with the same oil. Far more trustworthy is the close test first proposed by Keates about 1870, the principle of which is to heat the oil within a close vessel which is opened only from time to time to apply a light to its atmosphere. For the execution of this test many varieties of apparatus have been proposed. That adopted by Abel, and now (1884) legally recognized in Great Britain, is made of sheet copper, the exact thickness of which is prescribed for every part. The oil is placed in a close cup, suspended in an air-bath, which latter is heated by immersion in a warm-water bath, provided with an air-jacket. The top of the oil cup is pierced with three circular orifices, one in the centre for trying the best flame, and two smaller lateral holes for admitting air at the close of each trial. The holes are covered by a slide so contrived that when the central hole has become almost uncovered the lateral ones are also open. The slide carries a small colza-oil lamp suspended on trunnions, having a flame of a prescribed size. A pendulum two feet in length vibrates in front of the observer, who, in testing, withdraws the slide slowly during three vibrations, tilts the lamp to bring its flame in contact with the atmosphere of the vessel, and quickly shuts the slide during the fourth vibration. To execute a test the oil at about 60° F. is placed in the cup, which is immersed in the water-bath having water of 130° F. A thermometer plunged into the oil and another in the water-bath indicate their temperatures. When the oil has approached its presumable flashing point, trials are made at each rise of 1° F. in the temperature of the oil. The lowest temperature at which the atmosphere of the cup inflames is the flashing jioint of the oil tested. The legal minimum flashing point of burning oil by the close test is 75° F., corresponding to about 100°F. by the obsolete open test.
The variety of mixed paraffins which the oil-distiller produces may be arranged under the following heads :— (1) oils too volatile to be available for domestic illumina-tion, serving chiefly as solvents; (2) burning oils, as required for house lamps; (3) oils of very high boiling point, available, and used chiefly, for lubricating purposes ; (4) solid paraffin.
The products of the second class have long come to practically supersede the colza oil which used to be the illuminating oil par excellence. Over it they offer the advantages of greater cheapness and of giving, weight for weight, more light. But their drawbacks are that, how-ever carefully refined they may be, they have, when allowed to leak out, or in lamps of inferior construction, a somewhat disagreeable pungent odour, and that there is always a lurking danger in the possible presence of highly volatile inflammable hydrocarbons. Colza oil will never burn without a wick; paraffin oil or petroleum may do so.
Products of the second and third classes, separately or combinedly, are of course available as fuels proper, i.e., for the production of heat. At the time when mineral oil was first produced in great quantity in America, the advantages it would offer as a fuel for marine boilers especially were very emphatically insisted on. Of course mineral oil can be more economically stored than coal, and its combustion-heat is susceptible of more exhaustive utilization. The latter fact forms the raison d'etre of those beautiful petroleum kitchen-stoves and culinary lamps which are very much used on the Continent where gas is not at hand. But to talk of mineral oil as a cheap fuel for wholesale heating is nonsense. H. St Claire Deville, about 1870, made an extensive investigation on the calorific value of American petroleum which, as we know, is pretty much the same thing as paraffin oil. He used a large apparatus, enabling him to burn several hundred litres of oil in one experiment; in fact he realized more fully than other experimenters had ever done the conditions prevailing in the working of steam-boilers; the only difference was that he took care to collect all the heat produced in a large mass of water of known weight, and measured the heat by the increase of temperature produced in this heat receptacle. He found that even heavy Virginia lubricating oil gave not more than 10,180 units of heat (Centigrade) per unit-weight of fuel burned. But, on the other hand, in direct experiments made by Scheurer-Kestner, a coal containing 88 "4 per cent, of carbon, 4'4 of hydrogen, and 7'2 per cent, of oxygen, nitrogen, and ash gave 9628 units of heat, while another coal of the same elementary composition gave 9117 units. Gas retort coke (though a far closer approximation to pure carbon) yields only 8050 units. Supposing coal yielded just that in opposition to the 10,000 units from petroleum, it is clear that the latter must not cost more than 1 "25 times as much as coal weight for weight, or else it is the more expensive fuel. Take one ton of coal at 10s.; eight-tenths of a ton of petroleum is its calorific equivalent; but this weight of the oil (taking the specific gravity at 0"8) measures 224 gallons. Hence petroleum, to be as cheap as coal, must not cost more than about a halfpenny a gallon. Cheap as mineral oil is nowadays, it has not yet come down to this level.
To pass to the lubricating oil (third class), it, like the burning oil, competes with the fats and fatty oils which until lately were exclusively employed. In opposition to these it offers other and very substantial advantages besides its lower price. Good mineral lubricating oil may have such very high flashing point that it may be positively less inflammable than fatty oils or tallow; and, as a lubricant for high-pressure steam cylinders, it offers the great advantage that it is not, like fatty oils, decomposed by hot steam into glycerin and fatty acids, which latter cannot but attack the metal of the machinery to some extent. A still more important feature in mineral lubricating oil is that, even when diffused throughout a mass of cotton (or other textile) waste, it shows no tendency towards spon-taneous combustion. In exhaustive experiments by Galletly and by Coleman, it was found that mineral lubricating oils diffused through textile waste do not take fire at temperatures at which even colza oil ignites, and also that fatty lubricants to which from 20 to 50 per cent, of mineral oil was added were thereby prevented from igniting.
Solid paraffin, industrially and commercially, is a sub-stitute for the more expensive stearin as a material for candles. To this latter it is more than equivalent in light-giving power; but it offers the drawback of greater soft-ness and lower fusing point. In practice paraffin is always alloyed with stearin to produce candles possessing the necessary degree of hardness and stability of form.
The Paraffin Oil Industry of Scotland.
In December 1847 Lyon Playfair drew the attention of the late Mr James Young, F. R. S., a Glasgow chemist, to a spring or exuda-tion of petroleum at Alfreton in Derbyshire, and induced him to lease the spring, with the view of turning the material to commercial advantage. In 1848 Mr Young commenced the purification and preparation from this petroleum of two varieties of oil—one, thick, for lubricating, the other, thin and limpid, for burning in lamps. It was found that this crude petroleum contained paraffin in notable proportion; but the solid paraffin was not separated for trade purposes, and that body continued still a simple chemical curiosity. Within two years the quantity of petroleum yielded by the spring began to decrease, and in the beginning of 1851 it was practically exhausted, and the business there ceased. Meantime it had occurred to Mr Young that the petroleum he was working might have been produced by the action of heat on the underlying coal; and, under the impression that it might be possible by artificial means to pro-duce a similar substance, he began an extensive series of experiments on the destructive distillation of coal. As the result of a long-continued investigation in this direction, with many varieties of coal, Mr Young in October 1850 secured a patent for the manufacture of paraffin and paraffin oil from bituminous coal, which patent became the basis of the new industry. "The coals," the patentee says, " which I deem to be best fitted for the purpose are such as are usually called parrot coal, cannel coal, and gas coal, and which are much used in the manufacture of gas for the purpose of illumination." Early in 1850 Mr Young's attention wras called to the Boghead mineral, which he found to be of all the substances experimented upon the most promising for his purpose. That circumstance determined Mr Young and his original partners to set up their works at Bathgate in the region of the Boghead mineral, where con-sequently, in 1850, the necessary buildings and plant were erected, and manufacturing operations were begun in 1851. In 1853 a law-suit of great importance, which turned on the scientific question " What is coal ?" took place between the proprietor of a portion of the Boghead mineral and his mineral tenant, who was entitled to work coal only. The proprietor averred that the mineral in question was not coal; but, after a great amount of scientific evidence on both sides had been heard, the decision was that the substance came, so far as regarded the purposes of the lease, within the definition of coal. Had the issue of the case been in favour of the proprietor of the mineral, Mr Young's patent would have been practically valueless, for he claimed only the distillation of bituminous coal. The dis-tillation of mineral schists or shale at a low red heat had, moreover, been previously patented by Du Buisson; and the only raw materials which have been used to any extent in the Scottish industry are the Boghead mineral and subsequently bituminous shale.
The essential feature of Young's invention was the distillation of bituminous substances at the lowest temperature at which they could be volatilized to a practically sufficient extent. In practice it was found that a temperature of 800° F. is the point about which the best results are obtained.
The material exclusively distilled in the early years of the industry in Scotland was the Boghead cannel or Torbanehill mineral. The supply of this mineral was limited, and, as its value for gas-making as well as for oil-distilling was very great, it rapidly advanced in price from 13s. 6d. per ton, at which it was contracted for when the Bathgate works began operations, till it rose to 90s. per ton before its final disappearance from the market about 1866. As early as 1859 the bituminous shales which are found in the Scottish Carboniferous formation began to attract attention as a possible source of raw material for the industry, and in that year a seam was experimentally opened up at Broxburn, Linlithgowshire. In 1861 a shale oil work was established at Gavieside, West Calder, and by the period of the expiry of Young's patent in 1864 several works distilling shale were in operation. But, while from the Bog-head mineral from 120 to 130 gallons of crude oil were obtainable for every ton distilled, the ordinary bituminous shales yield at most only 35 gallons per ton ; and even with the improved methods of working in use at the present day the average yield of crude oil from shales is not more than 32 gallons per ton.
The bituminous shales of Scotland are found in a wide belt of the Carboniferous formation, extending from Ayrshire in a north-easterly direction to the Fife coast. In Ayr and Renfrew they are found to some extent in the true Coal-measures; but, generally, and especially in the east, they are obtained in the Lower Carboniferous series. These oil shales consist of fissile argillaceous bands, highly impreg-nated with bituminous matter. As a rule the shale of the west country yields a high percentage of crude oil, but the Linlithgow, Midlothian, and Fife shales produce oils comparatively rich in lubricating oil and solid paraffin, the most valuable product of the industry. The ordinary Broxburn shale contains 17 per cent, of bituminous volatile matter, and leaves 76 per cent, of spent shale (char) on distillation. In contj.ast with this is the composition of the Boghead mineral, which contained not less than 65 per cent, of volatile bituminous matter and only 22 per cent, of ash.
In the early years of the industry at Bathgate, the two classes of oil—heavy (lubricant) and light (illuminating)—were the products to which attention was principally directed. Paraffin was separated from the heavy oils ; but the demand for it was at first small, and many difficulties had to be overcome before candles consisting principally of that body could be favourably brought into the market. With the increased knowledge, improved methods, and eager competition of the present day, the range of products has largely extended, and almost everything obtainable from the shale, except the incombustible ash, is turned to profitable account. The commercial products embrace sulphate of ammonia, illuminating and heating gas, gasoline and naphtha, highly volatile oils, several grades of burning oil and of lubricating oil, heavy green oil used for making oil gas, and solid paraffin. The sequence of manufacturing operations has not changed in any essential particular since first established by Young; but at every stage and in all the appliances numerous and important modifications have been, and continue to be, actively introduced, all tending to greater economy of work, increase of production, and improvement of the quality and variety of commercial products.
Manufacturing Operations.
The manufacture divides itself into two distinct sections :—(1) the crude works, dealing with the preparation and distillation of the shale and with the production of crude oil and the collateral products — illuminating gas, gasoline, and ammonia ; and (2) the refinery, in which the crude oil is purified and separated or split up into the considerable range of commercial products obtainable from it. The following table shows the stages through which the various pro-ducts are derived from shale:—
Illuminating gas, partly burned and > ) A 1 Gasoline
partly condensed to form gasoline. ) f
' A. Naphtha f A 2. Solvent naphtha.
f B 1. Naphtha ) A3. Burning naphtha.
A 4. Burning oil.
Crude oil.
( Once-run oil. \ Coke.
_ B. Burning portion.
B 2. Burning fraction.
[ Burning oil of various densities.
) Intermediate oil with soft) 1. Intermediate oil.
( scale. ) 2. Soft scale.
Ammoniacal liquor.
"With sulphuric acid =Sulphate of ammonia.
scale. (C 2. Hard scale.
)
~ Paraffin of high melting point.
I B 3. Heavy oil with soft \ 1. Lubricating oils, various
scale. f densities.
C. Heavy oil with hard ( C J' Seavy oil with soft [ 2" Soft scale'
Grade, Works.—Bituminous shale as brought from the pits is passed through powerful toothed cylinder machinery, reducing it to fragments not larger than a man's fist. In this state it is conveyed in hutches to the retorts, in which it undergoes destruc-tive distillation—the distinctive operation under Mr Young's patent. The retorts used have undergone many and important modifications. Originally, as was natural, horizontal retorts arranged in benches, in all respects like gas retorts, were employed, but these in the Scottish trade very quickly gave way to the verti-cal retort. The form of vertical retort originally in general use consisted of a cast-iron cylinder, circular or oval in cross section, 8 or 10 feet in height and about 2 feet in diameter, or equivalent thereto. It tapered at the top, where it was provided with a hopper for charging the material to be distilled and a valve for closing the retort mouth. The bottom end dipped into a trough of water, forming an efficient lute, and effectually preventing the escape downwards of any of the gaseous products of distillation. These retorts were arranged in linear benches of six, three on each side of a furnace fed with coal, the heat from which passed to each side into the chamber or oven in which the retort stood. The distilled vapours passed away by a pipe at the upper end of the retort, their emission being aided by a jet of superheated steam injected at the bottom. The distillation in these retorts was continuous, a portion of spent shale being withdrawn through the water in the trough every hour or thereby, and a corresponding amount of fresh shale being added by the hopper.
As competition with American petroleum increased, the efforts of manufacturers were directed to cheapening the distilling process, by utilizing the spent shale from the retorts in its hot condition as fuel for distilling the succeeding charge. The difficulties in the way of accomplishing this were very great, chiefly on account of the large proportion of ash in the coked residue, amounting to from So to 90 per cent, of the whole. To use spent shale so poor in carbon it was essential that it should be dropped into the fur-nace direct from the retort without exposure to the air, and this was first successfully accomplished by the improved retorts and furnace patented by Mr Norman M. Henderson in 1873. According to the Henderson system, which has been adopted in the more important Scottish oil works—a series of four vertical retorts are arranged in quadrangular order over a common fire-chamber or furnace ; the bottom ends of the retorts are provided with doors capable of being closed gas-tight; and immediately below each door there is a valve which, in one position, and while the charge is being distilled, entirely cuts off the retort bottom from the furnace or fire-chamber, leaving the retort bottom exposed to the external air, but when the retort charge has been exhausted of oil, and is about to be passed into the furnace as fuel, the valve can be turned over outwards, in which position it forms an inclined shoot contiguous to the bottom of the retort and the fire-chamber. The door-closing at the bottom of the retort having been first withdrawn, and the valve drawn back, the contents of the retort pass freely into the furnace, where their combustion is at first assisted by a jet of the incondensible inflammable gas given off by the retorts themselves.
Each Henderson retort can contain about 18 cwt. of shale. The four retorts forming a set are being cleared in rotation at intervals of five hours, so that each charge suffers distillation for twenty hours. The temperature is kept at about 800° F., this giving the best results. The vapour produced in the retort is led off by a pipe issuing from near the bottom, and, in order to avoid unnecessarily prolonged sojourn of the vapour in the hot vessel, a jet of superheated steam is constantly made to stream in above and guide the vapour downwards. The vapour, which amounts to about 3000 cubic feet per ton of shale distilled, is passed through a system of condensing pipes, communicating below through a pro-perly divided horizontal chest, like that used in gas works for the condensation of the tar. From the last compartment of the con-denser the still uncondensed gas is drawn away by a fan or other "exhaust" through a set of "scrubbers." In the first of these the gas is washed with water and thus stripped of what it still contains of ammonia ; in the succeeding ones it is washed with heavy oil, which withdraws a considerable portion of the vapours of the more highly volatile hydrocarbons which are diffused throughout it. From this heavy-oil solution the absorbed hydrocarbons are extracted by distillation as "naphtha." The gas, after having thus been freed from its more readily condensible parts, is either led away into gas-holders to be utilized as illuminating gas or used directly as a fuel (see above). The product which collects in the condenser chests consists of crude oil (about one-fourth of it) and a weak aqueous solution of ammonia and volatile ammonia salts, containing from 2 to 5 per cent, of real ammonia, NH3, which, however, in all cases represents only a small percentage of the potential ammonia which was contained in the original shale in the form of nitrogenous carbon compounds. In the golden days of paraffin oil making this ammonia liquor was simply allowed to go to waste ; but wdien the American petroleum began to depress the prices of the oils the manufacturer saw the propriety of working up the liquors for sulphate of ammonia by the same methods as are employed in connexion with the coal-gas industiy (see NITROGEN, vol. xvii. p. 519). And as, during the last decade or two, the demand for ammonia has been steadily increasing, the ammonia in the shale industry by and by rose from the rank of a minor collateral to that of one of the principal products, and a number of attempts have been made to recover that part of the nitrogen which, in the ordinary process, is lost as a com-ponent of the coke. Dr H. Grouven proved (1875-77) that all nitrogenous organic or organoid matter when exposed to a current of steam at about 1000° C. burns into carbon oxides, hydrogen, and ammonia, the last-named including all the nitrogen. Messrs G. T. Beilby and William Young have worked out and patented a process for discounting this fact in the shale industry for a more exhaustive extraction of the ammonia. In one of the later forms of the process the shale is being distilled in retorts standing over a fire-brick chamber surrounded by flues and kept at a far higher tem-perature than the retorts themselves. The coke from the retorts is discharged straight into this chamber, and therein exposed to a mixed current of steam and air, which burns away the carbonaceous part into carbonic acid, carbonic oxide, hydrogen, and ammonia. The large mass of hot gas thus produced passes next through the retorts above to aid in the distillation, and conjointly with the retort vapour is subjected to systematic successive condensation. The incondensible gas which is ultimately obtained includes all that the gas from the ordinary process contains, and also a large pro-portion of hydrogen and carbonic oxide from the hot-chamber process. It serves as a fuel for heating the chamber and the retorts ; but, as it does not furnish quite enough of heat for all this, a combined retort and gas-producer is built into the bench with the shale retorts. This supplementary apparatus is charged with coal, which, in it, is first distilled, then converted partially into gas by steam and at last completely by a regulated cur-rent of air. The gas from the first and second stages is scrubbed to strip it of its ammonia and tar, and then, conjointly with the gas from the third, used as a fuel for the retorts. In this way the advantages of gas-firing are secured at little expense, as the condensed products are nearly equivalent in money value to the coal consumed. In the Young-Beilby process, which is extensively used in Scottish works, the yield of ammonia is on the average double, and in special cases five times, that obtained in the ordin-ary process of distillation.
The Working of the Oil.—The composition of the crude oil is very variable (see above). It generally forms a very dark green, almost black, liquid, somewhat tarry in appearance, and endowed with a highly unpleasant empyreumatic odour. The specific gravity ranges from 0 '862 to 0 '895. Each ton of shale distilled yields on an average 30 gallons of crude oil (about 260 lb), 700 lb of coke, gas, and loss, and 1270 lb of cinders. The crude oil on refining yields 38 to 44 per cent, of oils available as " spirit" or for burning, 15 to 20 per cent, of lubricating oil, and 9 to 12 per cent, of solid paraffin.
Refinery.—The first operation in oil refining consists in submit-ting the crude oil to distillation in large pot-shaped stills capable of holding 1200 or 1400 gallons. The distillation is continued till only a pure vesicular coke remains in the still, and the vapours (condensed by the ordinary worm-pipe arrangement) constitute "once-run oil," which from its bright green colour is also known as green oil. The once-run oil is the material from which, by a repeated series of washings with sulphuric acid and caustic soda and fractional distillations, the graduated series of purified pro-ducts is finally obtained.
Washing.—Once-run oil contains a series of basic and acid com-ponents. To separate these the oil is first repeatedly treated with sulphuric acid of different degrees of strength, which is thoroughly intermixed and brought in contact with the oil by mechanical means in an agitating tank or washer. The acid first used is a weak tarry acid which has been already used in a subsequent stage of the manufacture. This produces a copious tarry deposit, which is removed ; the process is repeated with a similar result ; and there-after the oil is further treated with two successive washings of strong vitriol. After settling and removal of the precipitated tars, a similar series of washings with caustic soda solutions of increasing strength, and corresponding precipitation and removal of tars which combine with the alkali, are carried out. During both the acid and the soda treatments the oil is maintained at a tempera-ture of about 100° F. by the circulation of steam through the tanks in coiled pipes. The sulphuric acid tars are to some extent used as fuel in the fractionating stills.
Fractional Distillation. —The purified once-run oil is a very mixed substance, giving off vapours within a wide range of temperatures, which condense into products of varied specific gravity. By the series of fractional distillations to which it is submitted a series of products are ultimately obtained comparatively homogeneous in constitution, which distil within relatively narrow limits of tem-perature. The ordinary method of fractionating once-run oil consists in running it into large cylindrical boiler stills heated by furnaces in which the acid tar already spoken of is consumed. The stills have led into them steam-pipes, through which steam is injected into the oil in process of distillation as required. When the heat is first raised, superheated steam is injected to aid in carry-ing off the lighter vapours, wdiich are condensed as naphtha or "spirit." As the distillation proceeds, and the gravity of the con-densed product increases, it is run into separate receivers, and thus a series of fractionated intermediate products is produced, the first portion up to 0750 specific gravity being naphtha, while from 6'750 to 0'850 is the burning oil portion, and the subsequent portion separated is heavy oil containing paraffin. The portion remaining in the still is removed to the residue stills, in which it is distilled till the still contains only coke. The oil driven off from the residue stills is called "heavy oil and paraffin," and passes to the paraffin house for treatment there.
Improved Fractionating Stills. —Many attempts have been made to adapt the fractionating still to a system of continuous working by keeping the contents at a constant level as the distillation pro-ceeds. For a long period continuous distillation was only imper-fectly applicable, and yielded unsatisfactory results. The lighter fractions aloue were driven off, and as the distillation progressed the density of the contents of the still gradually increased, making the difference between the oil added to the still and that within it increasingly great. In the end the contents of the still had to be removed and completely distilled as one charge in a separate still. In 1883 Mr Norman M. Henderson, the patentee of the Henderson retort, patented a continuous process of distillation which com-pletely obviates all difficulties, and largely reduces the time, labour, and cost of fractionation as compared with the ordinary intermittent method. According to Henderson's system, purified once-run oil is fractionated continuously in a connected series of three cylindrical stills. Each still is fitted with inlet and outlet pipes, the mouths of which opening upwards are placed at opposite extremities of the still. The outlet pipe of No. 1 passes as inlet into No. 2, and similarly outlet of No. 2 is connected as inlet with No. 3, while the outlet of No. 3 passes into one or more common residue stills. The inlet or feed pipe of No. 1 traverses the long horizontal con-densing pipes of the whole three, and thus the once-run oil, while absorbing heat before entering No. 1 still, also aids the condensation of the vapours. In working there is a constant feeding of heated once-run oil into No. 1 still, a like steady flow from No. 1 to No. 2, from No. 2 to No. 3, and from No. 3 to a residue still. The oil of course increases in density as it passes onwards ; but the specific gravity in each still is practically constant, and, as the heat applied is increased in proportion to the gravity, the oil vaporized in each separate still is of uniform quality and specific gravity. In No. 3 still, where, in consequence of the high gravity and temperature, there is a tendency to deposit carbonaceous matter, circulating plates or dishes hinged to each side of the still, and concentric with the bottom shell, are placed. The circulation of the oil from the bottom up the sides in the space between the shell and the circulating plates is directed and assisted by jets of steam from a pipe laid along the bottom of the still. In this way the oil is kept in steady circulation up the sides and down the centre, and any deposit of coke which may take place forms on the inner surface of the circu-lating plates, from which there is provision for its easy removal when required.
The manufacturer has now his material split up into three pro-ducts—naphtha, burning oil, and heavy oil with paraffin. By renewed treatments with acid and alkali and fractional distilla-tions, these products are further purified and differentiated. We cannot go into technical details, and in regard to the principles upon wdiich the processes are founded reference may be made to what has been said above in connexion with corresponding laboratory methods. As a final result the following products (or a similar series of other products) are produced and sent out into the market:—
1. Gasoline : a mixture of paraffins, so volatile that a current of air by being passed through it at ordinary temperatures is converted into combustible (non-explosive) gas.
2. Naphtha : a mixture of hydrocarbons which in volatility and otherwise are equivalent to the crude benzol of tile coal-gas industry.
3. Burning oil: a mixture of oils sufficiently volatile and light to be suitable for combustion in domestic lamps with wicks, and yet practically free of dangerously volatile inflammable components.
4. Heavy oil, corresponding to a range of very high boiling points; too heavy or viscid to be raised by the wick of a lamp, but well adapted for lubricating purposes. This part contains the solid paraffin Which the manufacturer takes care to extract as completely as possible before the oil is sold as "lubricating oil." The several kinds of crude paraffin extracted are classed as "hard scale" or "soft scale," according to their fusing points and consequent degrees of hard-ness at ordinary temperatures.
Separation of Hard Scale.—The heavy oil forming the last of the three portions into which once-run oil is fractionated, at ordi-nary atmospheric temperatures, becomes thick and pasty by the abundant formation of crystals of solid paraffin. This mixture of oil and paraffin is separated by draining through canvas bags, or, as is now the almost universal practice, by passing the magma into a filter press. This apparatus contains a series of thirty or forty perforated plates about 2 feet square, the faces of which are covered with filtering canvas. They are screwed up together in an oblong horizontal frame, so that a space or chamber about an inch wide is left between each pair of plates. Into these chambers the pasty mixture is forced under high pressure, the material pass-ing into and filling each chamber through an orifice in the centre of the plates till the whole of the chambers are filled. The pressure being kept up, the fluid oil exudes through the canvas and perforations in the plates, leaving solid paraffin, wdiich continues to accumulate till the chambers are filled with it in a comparatively dry condition. The soft cake from the filter press is further squeezed in canvas in an hydraulic press giving off more fluid oil, and the cake from this pressure consists of commercial hard scale or crude paraffin.
Soft Scale.—The heavy oils separated in the second and third fractionation of burning oils, and the oil from which the above hard scale is separated, hold dissolved in them paraffin of low melting point, which can only be crystallized out by bringing the oil to a very low temperature. For this purpose the oils are reduced to from 18° to 20° F. by artificial refrigeration. The method now employed consists in sufficiently cooling a continuous current of brine or of chloride of calcium solution by passing it through an ether refrigerating machine. This cold current of brine circulates through the interior of a large cylinder or drum, which revolves slowly, dipping into a trough containing the oil to be cooled. The cold surface of the drum in contact with the oil takes on a deposit of solid paraffin crystallized out of the mixture. It is removed by scrapers and made to fall into a separate receptacle, whence it goes to the filter press and the hydraulic press in the same way as the hard scale.
Lubricating Oil.—The oil from which hard and soft paraffin are separated as above stated exhibits a blue fluorescence, and is hence called blue oil. It receives an acid and soda series of washings, after which it is submitted to fractionation. The first portion given off, up to about 0'850 specific gravity, is transferred to the burning-oil series, with which it is mixed for further treatment. The remainder is received as various grades of lubricating oil, with specific gravity ranging from 0'860 to 0'890. These heavy oils are again refrigerated, yielding a further crop of soft scale, after which they get a final acid and alkali treatment, and are finished for use by having steam blown through them for a prolonged period, the effect of wdiich is to reduce greatly their objectionable smell. Finally they are kept in warm settling tanks at a temperature of not less than 90° F. for eight or ten days, when they are ready for the market.
Occasion has already been taken to name the advantages which this kind of mineral oil offers as a lubricating agent. Let us now add that it cannot quite take the place of fatty lubricants, lack-ing the degree and kind of viscosity which fits these for certain purposes. A mixture of fatty and mineral oil in proper proportions is often found to work better than either component would by itself. As mineral oil is far cheaper than all the fatty oils, it is largely used as adulterant of these. Sftch adulteration can often be detected without the aid of chemical tests ; all heavy mineral oils exhibit a characteristically strong blue fluorescence, which becomes rather more prominent by the presence of fatty oil. Manufacturers, however, have learned to remove the fluorescence by the addition of certain chemical substances, and large quanti-ties of such "bloom!ess" oil are being sold and used as colza or other fatty oil.
Paraffin Refining.—The crude paraffin which remains to be dealt with consists of soft scale, melting point between 90° and 105° F., and hard scale melting between 115° and 120° F. The greater part of the soft scale is disposed of in the crude state for impreg-nating match splints in lucifer-match making. The remainder, hard and soft, is purified by an acid and soda treatment, and decolorized by repeated washings with solvent naphtha. To this end the scale is melted, mixed with 25 per cent, of naphtha, cooled down, aud thus caused to crystallize, and subjected to hydraulic pressure. The solvent naphtha is thus squeezed out, and this series of operations is repeated two or three times. Each of the mother-liquors produced is utilized as a purifying agent for the paraffin of a^preceding stage of purity, so that it at last arrives at and serves for the original crude scale.
In its progress through these washings the naphtha takes up much heavy oil and solid paraffin, which are extracted by systematic fractionation and crystallization. The paraffin, after its last squeez-ing, is a dull chalky-looking white mass strongly impregnated with naphtha, to' drive off which it is melted and has a current of steam blown through it, till no trace of naphtha odour comes away with the steam. The ultimate decolorization is effected by mixing the heated paraffin with animal charcoal, allowing the charcoal to settle, and drawing off'the paraffin through filters. The molten paraffin flows into oblong tins which mould it into the beautiful translucent blocks used for candle making and the several other purposes to which paraffin is applied.
The soda-tar obtained in the various processes is to some extent collected and treated for the recovery of a soda sufficiently pure to be used in the first stages of purification of the crude oil. It is also employed to neutralize the acid tar, after which both are distilled, yielding as a bye-product an oil known as "green oil," largely used for the manufacture of oil-gas under Pintsch's patent.
Commerce.—The development of the paraffin industry under Young's patents, and the rapid increase of demand for the products, led directly to the rise of the great petroleum industry in America. The United States acting commissioner of patents, Mr John L. Hayes, in reporting on Mv Young's claim for an extension of his patent rights, states that " the manufactures of coal oil in this country had their origin in Mr Young's discovery. The use of petroleum followed so directly and obviously from the use of coal oils that it can hardly be denied that the one originated from the other." The petroleum industry once started, however, grew with so startling rapidity, and attained such gigantic proportions, that it threatened the entire extinction of the parent manufacture. In the early days of the trade a considerable development of manufacturing activity took jdace in "Wales, where an inferior kind of cannel coal was distilled ; and at many localities in Germany brown coal and sometimes peat were utilized as the raw materials of a considerable industry. The pressure of the competition with American oil was felt severely by all, and it was only with much difficulty that the great Scottish companies succeeded in holding their own, and in carrying on a constantly extending production. The Welsh industry was practically extinguished, and the production in Germany, not-withstanding the imposition of high protective duties, was greatly circumscribed. The chief seats of the manufacture in Germany are now in Saxony, near Weissenfels, where a peculiar variety of lignite called " pyropissite " forms the raw material for distillation.
In the Scottish industry there was in the middle of 1884 about £2,000,000 of capital invested, the working capacity of works in operation being equal to the distillation of 4170 tons of shale a day, while plant is being provided to increase that capacity to 5920 tons. The following table represents the present output of a year of 312 working days.
Actual. In View. Total.
Crude oil produced, gallons.. „ Burning oil and spirit, in
Lubricating oil, tons (of about Sulphate of ammonia, tons... ,, 4,170 1,301,040 39,031,200
400,070
24,490 15,334 10,454 1,750 546,000 16,380,000
167,895
10,277 6,435 4,388 5,920 1,847,040 55,411,200
567,965
34,767 21,769 14,842
(W. D.—J. PA.)