# Popular Science Monthly/Volume 27/June 1885/The Fuel of the Future

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* THE FUEL OF THE FUTURE.
By GEORGE WARDMAN.
THE practical application of natural gas, as an article of fuel, to the purpose of manufacturing glass, iron, and steel, promises to work a revolution in the industrial interests of America—promises to work a revolution; for, notwithstanding the fact that, in many of the largest iron, steel, and glass factories in Pittsburg and its vicinity, natural gas has already been substituted for coal, the managers of some such works are shy of the new fuel, mainly for two reasons: 1. They doubt the continuity and regularity of its supply; 2. They do not deem the difference between the price of natural gas and coal sufficient, as yet, to justify the expenditure involved in the furnace changes necessary to the substitution of the one for the other. These two objections will doubtless disappear with additional experience in the production and regulation of the gas-supply, and with enlarged competition among the companies engaging in its transmission from the wells to the works. At present the use of natural gas as a substitute for coal in the manufacture of glass, iron, and steel, is in its infancy.
Natural gas is as ancient as the universe. It was known to man in prehistoric times, we must suppose, for the very earliest historical reference to the Magi of Asia records them as worshiping the eternal fires which then blazed, and still blaze, in fissures of the mountain-heights overlooking the Caspian Sea. Those records appertain to a period at least GOO years before the birth of Christ; but the Magi must have lived and worshiped long anterior to that time.
Zoroaster, reputed founder of the Parsee sect, is placed contemporary with the prophet Daniel, from 2500 to 600 b. c.; and, although Daniel has been doubted, and Zoroaster may never have seen the light, the fissures of the Caucasus have been flaming since the earliest authentic records.
The Parsees (Persians) did not originally worship fire. They believed in two great powers—the Spirit of Light, or Good, and the Spirit of Darkness, or Evil. Subsequent to Zoroaster, when the Persian Empire rose to its greatest power and importance, overspreading the west to the shores of the Caspian and beyond, the tribes of the Caucasus suffered political subjugation; but the creed of the Magi, founded upon the eternal flame-altars of the mountains, proved sufficiently vigorous to transform the Parseeism of the conquerors to the fire-worship of the conquered.
About the beginning of the seventh century of the Christian era, the Grecian Emperor Heraclius overturned the fire-altars of the Magi at Baku, the chief city on the Caspian, but the fire-worshipers were ​not expelled from the Caucasus until the Mohammedans subjugated the Persian Empire, when they were driven into the Rangoon, on the Irrawaddy, in India, one of the most noted petroleum-producing districts of the world.
Petroleum and natural gas are so intimately related that one would hardly dare to say whether the gas proceeds from petroleum or the petroleum is deposited from the gas. It is, however, safe to assume that they are the products of one material, the lighter element separating from the heavier under certain degrees of temperature and pressure. Thus, petroleum may separate from the gas as asphaltum separates from petroleum. But some speculative minds consider natural gas to be a product of anthracite coal. The fact that the great supply-field of natural gas in Western Pennsylvania, New York, West Virginia, and Eastern Ohio, is a bituminous and not an anthracite region, does not, of itself, confute that theory; as the argument for it is, that the gas may be tapped at a remote distance from the source of supply, and, whereas anthracite is not a gas-coal, while bituminous is, we are told to suppose that the gas which once may have been a component part of the anthracite was long ago expelled by Nature, and has since been held in vast reservoirs with slight waste, awaiting the use of man. That is one theory; and upon that supposition it is suggested that anthracite may exist below the bituminous beds of the region lying between the Alleghany Mountains and the Great Lakes. Another theory is, that natural gas is a product of the sea-weed deposited in the Devonian stratum. But, leaving modern theories on the origin of natural gas and petroleum, we may suppose the natural gas jets now burning in the fissures of the Caucasus to have started up in flames about the time when, according to the Old Testament, Noah descended from Mount Ararat, or very soon thereafter. In the language of modern science it would be safe to say that those flames sprang up when the Caucasus range was raised from beneath the surface of the universal sea. The believer in biblical chronology may say that those fires have been burning for four thousand years—the geologist may say for four millions.
We know that Alexander the Great penetrated to the Caspian; and in Plutarch we read: "Hence [Arbela] he marched through the province of Babylon [Media?], which immediately submitted to him, and in Ecbatana [?] was much surprised at the sight of the place where fire issues in a continuous stream, like a spring of water, out of a cleft in the earth, and the stream of naphtha, which not far from this spot flows out so abundantly as to form a large lake. This naphtha, in other respects resembling bitumen, is so subject to take fire that, before it touches the flame, it will kindle at the very light that surrounds it, and often inflame the intermediate air also. The barbarians, to show the power and nature of it, sprinkled the street that led to the king's lodgings with little drops of it, and, when it was ​almost night, stood at the farther end with torches, which being applied to the moistened places, the first taking fire, instantly, as quick as a man could think of it, it caught from one end to another in such manner that the whole street was one continued flame. Among those who used to wait upon the king, and find occasion to amuse him, when he anointed and washed himself, there was one Athenophanus, an Athenian, who desired him to make an experiment of the naphtha upon Stephanus, who stood by in the bathing-place, a youth with a ridiculously ugly face, whose talent was singing well. 'For,' said he, 'if it take hold of him, and is not put out, it must undeniably be allowed to be of the most invincible strength.' The youth, as it happened, readily consented to undergo the trial, and, as soon as he was anointed and rubbed with it, his whole body broke out into such a flame, and was so seized by the fire, that Alexander was in the greatest perplexity and alarm for him, and not without reason; for nothing could have prevented his being consumed by it if, by good chance, there had not been people at hand with a great many vessels of water for the service of the bath, with all which they had much ado to extinguish the fire; and his body was so burned all over that he was not cured of it a good while after. And thus it is not without some plausibility that they endeavor to reconcile the fable to truth, who say this was the drug in the tragedies with which Medea anointed the crown and veils which she gave to Creon's daughter."
An interesting reference to the fire-worshipers of the Caucasus is contained in the "History of Zobeide," a tale of the wonderful Arabian Nights Entertainment. It runs thus:
"I bought a ship at Balsora, and freighted it; my sisters chose to go with me, and we set sail with a fair wind. Some weeks after we cast anchor in a harbor which presented itself, with intent to water the ship. As I was tired with having been so long on board, I landed with the first boat, and walked up into the country. I soon came in sight of a great town. When I arrived there I was much surprised to see vast numbers of people in different postures, but all immovable. The merchants were in their shops, the soldiery on guard; every one seemed engaged in his proper avocation, yet all were become as stone. . . . I heard the voice of a man reading Al Koran. . . . Being curious to know why he was the only living creature in the town, . . . he proceeded to tell me that the city was the metropolis of a kingdom now governed by his father; that the former king and all his subjects were Magi, worshipers of fire and of Nardoun, the ancient king of the giants who rebelled against God. 'Though I was born,' continued he, 'of idolatrous parents, it was my good fortune to have a woman governess who was a strict observer of the Mohammedan religion. She taught me Arabic from Al Koran; by her I was instructed in the true religion, which I would never afterward renounce. About three years ago a thundering voice was heard distinctly throughout the city, ​saying, "Inhabitants, abandon the worship of Nardoun and of fire, and worship the only true God, who showeth mercy!" This voice was heard three years successively, but no one regarded it. At the end of the last year all the inhabitants were in an instant turned to stone. I alone was preserved.'"
In the foregoing tale we doubtless have reference to the destruction of Baku, on the Caspian (though to sail from Balsora to Baku is impossible), and the driving away into India, by the Arabs under Caliph Omar, of all who refused to renounce fire-worship and adopt the creed of the Koran. The turning of the refractory inhabitants into stone is probably the Arabian story-teller's figurative manner of referring to the finding of dead bodies in a mummified condition.
It is known that the Egyptians made use of bitumen, in some form, in the preservation of their dead, a fact with which the Arabians were familiar. As the Magi held the four elements of earth, air, fire, and water to be sacred, they feared to either bury, burn, sink, or expose to air the corrupting bodies of their deceased. Therefore, it was their practice to envelop the corpse in a coating of wax or bitumen, so as to hermetically seal it from immediate contact with either of the four sacred elements. Hence the idea of all the bodies of the Magi left at Baku being turned to stone, while only the true believer in Mohammed remained in the flesh.
Marco Polo, the famous traveler of the thirteenth century, makes reference to the burning jets of the Caucasus, and those fires are known to the Russians as continuing in existence since the army of Peter the Great wrested the regions about the Caspian from the modern Persians. The record of those flaming jets of natural gas is thus brought down in an unbroken chain of evidence from remote antiquity to the present day, and they are still burning.
Numerous Greek and Latin writers testify to the known existence of petroleum about the shores of the Mediterranean two thousand years ago. More modern citations may, however, be read with equal interest. In the "Journal of Sir Philip Skippon's Travels in France," in 1663, we find the following curious entries:
"We stayed in Grenoble till August 1st, and one day rode out, and, after twice fording the river Drac (which makes a great wash) at a league's distance, went over to Pont de Clef, a large arch across that river, where we paid one sol a man; a league further we passed through a large village called Vif, and about a league thence by S. Bathomew, another village, and Chasteau Bernard, where we saw a flame breaking out of the side of a bank, which is vulgarly called La Fountaine qui Brule; it is by a small rivulet, and sometimes breaks out in other places; just before our coming some other strangers had fried eggs here. The soil hereabouts is full of a black stone, like our coal, which, perhaps, is the continual fuel of the fire. . . . Near Peroul, about a league from Montpelier, we saw a boiling fountain (as they ​call it), that is, the water did heave up and bubble as if it boiled. This phenomenon in the water was caused by a vapor ascending out of the earth through the water, as was manifest, for if that one did but dig anywhere near the place, and pour water upon the place new digged, one should observe in it the like bubbling, the vapor arising not only in that place where the fountain was, but all thereabout; the like vapor ascending out of the earth and causing such ebullition in water it passes through hath been observed in Mr. Hawkley's ground, about a mile from the town of Wigan, in Lancashire, which vapor, by the application of a lighted candle, paper, or the like, catches fire and flames vigorously. Whether or not this vapor at Peroul would in like manner catch fire and burn I cannot say, it coming not in our minds to make the experiment. . . . At Gabian, about a day's journey from Montpelier, in the way to Beziers, is a fountain of petroleum. It burns like oil, is of a pungent scent, and a blackish color. It distills out of several places of the rock all the year long, but most in the summer time. They gather it up with ladles and put it in a barrel set on end, which hath a spiggot just at the bottom. When they have put in a good quantity they open the spiggot to let out the water, and when the oil begins to come presently stop it. They pay for the farm of this fountain about fifty crowns per annum. We were told by one Monsieur Beaushoste, a chymist in Montpelier, that petroleum was the very same with oil of jet, and not to be distinguished from it by color, taste, smell, consistency, virtues, or any other accident, as he had by experience found upon the coast of the Mediterranean Sea, in several places, as at Berre, near Martague, in Provence; at Messina, in Sicily, etc."
In Harris's "Voyages," published in 1764, an article on the empire of Persia thus refers to petroleum:
"In several parts of Persia we meet with naphtha, both white and black; it is used in painting and varnish, and sometimes in physic, and there is an oil extracted from it which is applied to several uses, The most famous springs of naphtha are in the neighborhood of Baku, which furnish vast quantities, and there are also upwards of thirty springs about Shamasky, both in the province of Schirwan. The Persians use it as oil for their lamps and in making fireworks, of which they are extremely fond, and in which they are great proficients."
Petroleum has long been known to exist also in the northern part of Italy, the cities of Parma and Genoa having been for many years lighted with it.
In the province of Szechuen, China, natural gas is obtained from beds of rock-salt at a depth of fifteen to sixteen hundred feet. Being brought to the surface, it is conveyed in bamboo tubes and used for lighting as well as for evaporating water in the manufacture of salt. It is asserted that the Chinese used this natural gas for illuminating purposes long before gas-lighting was known to the Europeans. ​Remembering the unprogressive character of Chinese arts and industries there is ground for the belief that they may have been using this natural gas as an illuminant these hundreds of years.
In the United States the existence of petroleum was known to the Pilgrim Fathers, who doubtless obtained their first information of it from the Indians, for whom, in New York and Western Pennsylvania, it was called Seneka-oil. It was otherwise known as "British" oil and oil of naphtha, and was considered "a sovereign remedy for an inward bruise."
The record of natural gas in this country is not so complete as that of petroleum, but we learn that an important gas-spring was known in West Bloomfield, N. Y., seventy years ago. In 1864 a well was sunk to a depth of three hundred feet upon that vein, from which a sufficient supply of gas was obtained to illuminate and heat the city of Rochester (twenty-five miles distant) it was supposed. But the pipes which were laid for that purpose, being of wood, were unfitted to withstand the pressure, in consequence of which the scheme was abandoned; but gas from that well is now in use as an illuminant and as fuel both in the town of West Bloomfield and at Honeoye Falls. The village of Fredonia, N. Y., has been using natural gas in lighting the streets for thirty years or thereabout. On Big Sewickley Creek, in Westmoreland County, Pa., natural gas was used for evaporating water in the manufacture of salt thirty years ago, and gas is still issuing at the same place. Natural gas has been in use in several localities in Eastern Ohio for twenty-five years, and the wells are flowing as vigorously as when first known. It has also been in use in West Virginia for a quarter of a century, as well as in the petroleum region of Western Pennsylvania, where it has long been utilized in generating steam for drilling oil-wells.
In 1826 the "American Journal of Science" contained a letter from Dr. S. P. Hildreth, who, in writing of the products of the Muskingum (Ohio) Valley, said: "They have sunk two wells, which are now more than four hundred feet in depth; one of them affords a very strong and pure salt-water, but not in great quantity; the other discharges such vast quantities of petroleum, or, as it is vulgarly called, 'Seneka-oil,' and besides is so subject to such tremendous explosions of gas, as to force out all the water and afford nothing but gas for several days, that they make little or no salt."
The value of the foregoing references is to be found in the testimony they offer as to the duration of the supply of natural gas. Whether we look to the eternal flaming fissures of the Caucasus, or to New York, Pennsylvania, and Ohio, there is much to encourage the belief that the flow of natural gas may be, like the production of petroleum, increased rather than diminished by the draughts made upon it. Petroleum, instead of diminishing in quantity by the millions of barrels drawn from Western Pennsylvania in the last quarter ​of a century, seems to increase, greater wells being known in 1884 than in any previous year, and prices having fallen from two dollars per bottle for "Seneka-oil" to sixty cents per barrel for the same article under the name of crude petroleum. Hence we may assume that, as new pipe-lines are laid, the supply of natural gas available for use in the great manufacturing district of Pittsburg and vicinity will be increased, and the price of this fuel diminished in a corresponding ratio.
Natural gas is now supplied in Pittsburg at a small discount on the actual cost of coal used last year in the large manufacturing establishments, an additional saving being made in dispensing with firemen and avoidance of hauling ashes from the boiler-room. It is supplied, for domestic purposes, at twenty cents per one thousand cubic feet, which is not cheaper than coal in Pittsburg, but it is a thousand per cent cleaner; and in that respect it promises to prove a great blessing, not only to those who can afford to use it, but to the community at large, in the hope held out that the smoke and soot nuisance may be abated in part, if not wholly subdued, and that gleams of sunshine there may become less phenomenal in the future than they are at the present time. Twenty cents per thousand feet is too high a price to bring gas into general use for domestic purposes in a city where coal is cheap. Ten cents would be too much, and no doubt five cents per thousand would pay a profit. The fact is, the dealers in natural gas appear to be somewhat doubtful of the continuity of supply, and anxious to get back the cost of wells and pipes in one year, which, if successful, would be an enormous return on the investment.
There are objections to the use of natural gas by mill-operators—that it costs too much, and that the continuity of the supply is uncertain; by heads of families, that it is odorless, and, in case of leakage from the pipes, may fill a room and be ready to explode without giv ing the fragrant warning offered by common gas. Both of these objections will probably disappear under the experience that time must furnish. More wells and tributary lines will lessen the cost and tend to regulate the pressure for manufacturers. Cut-offs and escape-pipes outside of the house will reduce the risk of explosions within. The danger in the house may also be lessened by providing healthful ventilation in all apartments wherein gas shall be consumed.
This subject of the ventilation of rooms in which common gas is ordinarily used is beginning to attract attention. It is stated, upon scientific authority, that a jet of common gas, equivalent to twelve sperm-candles, consumes 5·45 cubic feet of oxygen per hour, producing 3·21 feet of carbonic-acid gas, vitiating, according to Dr. Tidy's "Handbook of Chemistry," 348·25 cubic feet of air. In every five cubic feet of pure air in a room there is one cubic foot of oxygen and four of nitrogen. Without oxygen human life, as well as light, would become extinct. It is asserted that one common gas-jet consumes as much oxygen as five persons.
​Carbonic-acid gas is the element which, in deep mines and vaults, causes almost instant insensibility and suffocation to persons subjected to its influences, and instantly extinguishes the flame of any light lowered into it. The normal quantity of this gas contained in the air we breathe is ·04; one per cent of it causes distress in breathing; two per cent is dangerous; four per cent extinguishes life, and four per cent of it is contained in air expelled from the lungs. According to Dr. Tidy's table, each ordinary jet of common gas contributes to the air of a room sixteen by ten feet on the sides and nine feet high, containing 1,440 cubic feet of air, twenty-two per cent of carbonic-acid gas, which, continued for twenty hours without ventilation, would reach the fatal four per cent.
Professor Huxley gives, as a result of chemical analyses, the following table of ratio of carbonic-acid gas in the atmosphere at the points named:
| On the Thames, at London | ·0343 |
| In the streets of London | ·0380 |
| Top of Ben Nevis | ·0327 |
| Dress circle of Haymarket Theatre (11.30 p. m.) | ·0757 |
| Chancery Court (seven feet from the ground) | ·1930 |
| From working mines (average of 339 samples) | ·7852 |
| Largest amount in a Cornish mine | 2·0500 |
In addition to the consumption of oxygen and production of carbonic acid by the use of common gas, the gas itself, owing to defectiveness of the burner, is projected into the air. Now, considering the deleterious nature of all illuminating gases, the reasons for perfect ventilation of rooms in which natural gas is used for heating and culinary purposes are self-evident, not alone as a protection against explosions, but for the health of the occupants of the house, remembering that a larger supply of oxygen is said to be necessary for the perfect combustion of natural than of common gas.
Carbonic oxide, formed by the consumption of carbon, with an insufficient supply of air, is the fatal poison of the charcoal-furnace, not infrequently resorted to, in close rooms, as a means of suicide. The less sufficient the air toward perfect combustion, the smaller the quantity of carbonic acid and the greater the amount of carbonic oxide. That is to say, at the time of ignition the chief product of combustion is carbonic oxide, and, unless sufficient air be added to convert the oxide to carbonic acid, a decidedly dangerous product is given off into the room. Yet, by means of a flue to carry off the poisonous gases from burning jets, the combustion of gas, creating a current, is made an aid to ventilation. Unfortunately, this important fact, if commonly known, is not much heeded by heads of families or builders of houses. But in any large community where gas comes into general use as an article of fuel, this fact will gradually become recognized and respected.
​The property of indicating the presence of very minute quantities of gas in a room is claimed for an instrument recently described by C. von Jahn, in the "Revue Industrielle." This is a porous cup, inverted and closed by a perforated rubber stopper. Through the perforation in the stopper the interior of the cup is connected with a pressure-gauge containing colored water. It is claimed that the diffusion of gas through the earthenware raises the level of the water in the gauge so delicately that the presence of one half of one per cent of gas may be detected by it. Other instruments of a slightly different character are credited by their inventors with most sensitive power of indicating gas-leakages, but their practical efficiency remains to be demonstrated. An automatic cut-off for use outside of houses in which natural gas is consumed has been invented, but this writer knows nothing of either its mode of action or its effectiveness.
The great economic question, however, connected with the use of natural gas is, How will it affect the industrial interests of the country? There are grounds for the belief that a sufficient supply of natural gas may be found in the vicinity of Pittsburg to reduce the cost of fuel to such a degree as to make competition in the manufacture of iron, steel, and glass, in any part of the country where coal must be used, out of the question. Such a condition of affairs would probably result in driving the great manufacturing concerns of the country into the region where natural gas is to be obtained. That may be anywhere from the western slope of the Alleghanies to Lake Erie or to Lake Michigan. And, if the cost of producing iron, steel, and glass can be so cheapened by the new fuel, the tariff question may undergo some important modification in politics. For, if the reduction in the cost of fuel should ever become an offset to the lower rate of wages in Europe, the manufacturers of Pennsylvania, who have long been the chief support of the protective policy of the country, may lose their present interest in that question, and leave the tariff to shift for itself elsewhere. It should be remembered that natural gas is not, as yet, much cheaper than coal in Pittsburg. But it may safely be assumed that it will cheapen, as petroleum has done, by a development of the territory in which it is known to exist in enormous quantities. It is quite possible that, instead of buying gas, many factories will bore for it with success, or remove convenient to its natural sources, so that a gas-well may ultimately become an essential part of the "plant" of a mill or factory. Even now coal can not compete with gas in the manufacture of window-glass, for, the gas being free from sulphur and other impurities contained in coal, produces a superior quality of glass; so that in this branch of industry the question of superiority seems already settled.
Having said thus much of an industry now in its infancy but promising great growth, I submit tables of analyses of common and of the natural or marsh gas, the latter from a paper recently prepared by a
TABLE OF ANALYSIS OF NATURAL GAS—FROM VARIOUS SOURCES.
Petroleum is composed of about 85 per cent of carbon and 15 per cent of nitrogen.
​committee of the Engineers' Society of Western Pennsylvania, and for the use of which I am indebted to that association:
COMMON GAS. :
| Hydrogen | 46·0 |
| Light carbureted hydrogen (marsh-gas) | 39·5 |
| Condensible hydrocarbon | 3·8 |
| Carbonic oxide | 7·5 |
| "acid | 0·6 |
| Aqueous vapor | 2·0 |
| Oxygen | 0·1 |
| Nitrogen | 0·5 |
| | 100·00 |
Natural gas is now conveyed to Pittsburg through four lines of 5$^5$⁄$_8$-inch pipe, and one line of eight-inch pipe. A line of ten-inch pipe is also being laid. The pressure of the gas at the wells is from 150 to 230 pounds to the square inch. As the wells are on one side eighteen and on the other about twenty-five miles distant, and as the consumption is variable, the pressure at the city can not be given. Greater pressure might be obtained at the wells, but this would increase the liability to leakage and bursting of pipes. For the prevention of such casualties safety-valves are provided at the wells, permitting the escape of all superfluous gas. The enormous force of this gas may be appreciated from a comparison of, say, 200 pounds pressure at the wells with a two-ounce pressure of common gas for ordinary lighting. The amount of natural gas now furnished for use in Pittsburg is supposed to be something like 25,000,000 cubic feet per day; the ten-inch pipe now laying is estimated to increase the supply to 40,000,000 feet. The amount of manufactured gas used for lighting the same city probably falls below 3,000,000 feet. About fifty mills and factories of various kinds in Pittsburg now use natural gas. It is used for domestic purposes in two hundred houses. Its superiority over coal in the manufacture of window-glass is unquestioned. That it is not used in all the glass-houses of Pittsburg is due to the fact that its advantages were not fully known when the furnaces were fired last summer, and it costs a large sum to permit the furnaces to cool off after being heated for melting. When the fires cool down, and before they are started up again, the furnaces now using coal will doubtless all be changed so as to admit natural gas. The superiority of French over American glass is said to be due to the fact that the French use wood and the Americans coal in their furnaces, wood being free from sulphur, phosphorus, etc. The substitution of gas for coal, while not increasing the cost, improves the quality of American glass, making it as nearly perfect as possible.
While the gas is not used as yet in any smelting-furnace nor in the Bessemer converters, it is preferred in open-hearth and crucible steel furnaces, and is said to be vastly superior to coal for puddling. ​The charge of a puddling-furnace, consisting of 500 pounds of pig-metal and eighty pounds of "fix," produces with coal-fuel 490 to 500 pounds of iron. With gas for fuel, it is claimed that the same charge will yield 520 to 530 pounds of iron. In an iron-mill of thirty furnaces, running eight heats each for twenty-four hours, this would make a difference in favor of the gas of, say, 8 X 30 X 25 = 6,000 pounds of iron per day. This is an important item of itself, leaving out the cost of firing with coal and hauling ashes.
For generating steam in large establishments, one man will attend a battery of twelve or twenty boilers, using gas as fuel, keep the pressure uniform, and have the fire-room clean as a parlor. For burning brick and earthenware, gas offers the double advantage of freedom from smoke and a uniform heat. The use of gas in public bakeries promises the abolition of the ash-box and its accumulation of miscellaneous filth, which is said to often impregnate the "sponge" with impurities.
In short, the advantages of natural gas as a fuel are so obvious to those who have given it a trial, that the prediction is made that, should the supply fail, many who are now using it will never return to the consumption of crude coal in factories, but, if necessary, convert it or petroleum into gas at their own works.
It seems, indeed, that, until we shall have acquired the wisdom enabling us to conserve and concentrate the heat of the sun, gas must be the fuel of the future.