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simpler, and yet equally effectual, with the best coal-gas apparatus. The retort is a bent cast-iron tube, which is heated red by a small convenient furnace, and into which oil is allowed to drop by a very ingenious apparatus; the oil is immediately volatilised, and the vapor in traversing the tube becomes perfectly decomposed. A mixture of inflammable gases, which contains a great portion of olefiant gas, passes off; it is washed by being passed through a vessel of water (which dissolves a little sebacic acid, and which seldom requires changing), and is then conducted into the gasometer.

The facility and cleanliness with which gas is prepared from oil, in the above manner, may be conceived from the description of the process. A small furnace is lighted, and a sufficient quantity of the commonest oil is put into a small iron vessel, a cock is turned, and the gas after passing through water in the washing vessel goes into the gasometer. The operation may be stopped by shutting off the oil, or, to a certain extent, hastened by letting it on more freely; the small quantity of charcoal deposited in the retort is drawn out by a small rake, and the water of the washer is very rarely changed.

The gas prepared from oil is very superior in quality to that from coal; it cannot possibly contain sulphureted hydrogen, or any extraneous substance; it gives a much brighter and denser flame; and it is also more effectual, viz. a smaller quantity will supply the burner with fuel. These peculiarities are occasioned, in the first place, by the absence of sulphur from oil, and then by the gas containing more carbon in solution. As the proportion of light given out by the flame of a gaseous compound of carbon and hydrogen is, in common circumstances, in proportion to the quantity of carbon present, it is evident that the gas which contains a greater proportion of olefiant gas, or supercarbureted hydrogen than coal gas, will yield a better and brighter light on combustion. It is necessary, in consequence of the abundance of charcoal in solution, to supply the gas when burning with plenty of atmospheric air; for as there is more combustible matter in a certain volume of it than in an equal volume of coal gas, it of necessity, must have more oxygen for its consumption. The consequence is, that less gas must be burnt in a flame of equal size, which will still possess superior brilliancy; that less is necessary for the same purpose of illumination; and that less heat will be occasioned. From five and a half to six cubical feet of coal gas are required to supply an Argand burner for an hour; two cubical feet to two and a half of that from oil, are abundantly sufficient for the same purpose. One important advantage gained by the circumstance, that so small a quantity of this gas is necessary for burners, is, that the gasometer required may be small in proportion. The gasometer is the most bulky part of a gas apparatus, and that least capable of concentration; and wherever it is placed, it occupies room to the exclusion of every thing else. Some very ingenious attempts have been made to diminish its size and weight, as in the double gasometer, and others, but without remarkable success. Here, however, where the

room required to contain the gas is directly diminished, the object is so far obtained; and when that takes place to one-half, or even onethird, it is of very great importance. It in a great number of cases brings the size of the apparatus within what can be allowed in private houses; and, in consequence of the rapidity with which the retort can be worked, the gasometer may again be reduced to a still smaller size. Another advantage gained by the small quantity of gas required for a flame is the proportionate diminution of heat arising from the lights. The quantities of heat and light produced by the combustion of inflammable gases are by no means in the same constant relation to each other: one frequently increases, whilst the other diminishes, and this is eminently the case when coal gas and oil gas are burned against each other. The quantity of heat liberated is, speaking generally, as the quantity of gas consumed, and this is greatest with the coal gas; but the quantity of light is nearly as the quantity of carbon that is well burnt in the flame; and this is greatest in the oil gas.

The very compact state in which the apparatus necessary for the decomposition of oil can be placed, the slight degree of attention required, its certainty of action, its cleanliness, and the numerous applications of which it admits, in the use of its furnace for other convenient or economical purposes, render it not only unobjectionable, but useful in manufactories and establishments; and these favorable circumstances are accompanied, not by an inferiority in the flame, or increased expense, but by an improved state of the first, and saving in the latter.

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Messrs. Taylors have shown great ingenuity in the construction of their whole apparatus, but the washer and gasometer deserve particular notice for their remarkable simplicity also. the washer, two planes are fixed in a box or cistern, in a direction not quite horizontal, but inclined a little in opposite directions; the planes are traversed nearly across by slips of wood or metal, fixed in an inclined position on the under surface, and which alternately touch one side of the cistern, leaving the other open and free. These planes being immersed in water, the gas is thrown in under the lowest ridge; and, by its ascending power, is made to traverse backward and forward along the ridges fixed on the planes, until it escapes at the highest part of the uppermost ridge. Thus, with a pressure of five or six inches of water only, it is made to pass through a distance of fourteen or sixteen feet under the surface of the fluid, and become well washed. The smaller gasometers are made of thin plate iron, and, being placed in a frame of light iron work, look more like ornamental stoves than the bulky appendages to gas apparatus, which they supply. The larger ones are made very light, and, when in pieces, very portable, by being constructed of a frame of wood work, in the edges of which are deep narrow grooves; plates of iron fit into these grooves, which, being caulked in and painted over, make a light and tight apparatus. These are easily put together in any place; and may therefore be introduced into a small apartment, or other confined space,

where a gasometer already made up would not

enter.

The general advantages of oil-gas, when contrasted with coal-gas, are as follows:-The material from which it is produced, containing no sulphur, or other matter, by which the gas is contaminated, there are no objections to its use, on account of the suffocating smell, in close rooms. It does no sort of injury to furniture, books, plate, pictures, paint, &c. All the costly and offensive operation of purifying the gas by lime, &c., is totally avoided when it is obtained from oil. Nothing is contained in oil-gas which can possibly injure the metal of which the conveyance pipes are made. The oil-gas, containing no unmixed hydrogen, which occasions the great heat of coal-gas, there is no greater heat in proportion from the flame of oil-gas than from burning oil in lamps, wax-candles, &c.

The apparatus for the production of oil-gas is much less expensive than that necessary to make coal-gas; it occupies much less space; it requires much less labor and skill to manage it; it is not so liable to wear and tear, and not so costly to repair as a coal-gas apparatus; there are no offensive products to remove; and, on its present improved construction, it may be introduced into any dwelling-house without nuisance. The economy of light from oil-gas may be judged of from the following data:-One gallon of common whale-oil will produce about ninety cubic feet of gas, and an Argand burner will require a cubic foot and a half per hour to maintain a perfect light; consequently, a gallon of oil, made into gas, will afford such a light for sixty hours, and the expense, at a moderate price of oil, will be, allowing for coals, labor, &c., not more for one burner than three farthings per hour.

Such a burner will be equal in intensity of light to two Argand oil-lamps, or to ten mould candles. The expense of Argand oil-lamps is usually admitted to be about 1d. per hour each. Supposing ten mould candles to be burning, at four to the lb., will be 24 lbs., costing 2s. 11d., one-tenth part will be consumed in each hour, and the cost of the light is then 34d. per hour. If wax-candles be employed, the expense of a quantity of light equal to a gas-burner, for one hour, by the same mode of reckoning allowing a candle to burn ten hours, and taking the price of wax-candles at 4s. 6d. per lb., will cost about

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gas, which renders so small a volume necessary that one cubic foot of oil-gas will be found to go as far as four of coal-gas. This circumstance is of great importance, as it reduces in the same proportion the size of the gasometers which are necessary to contain it; this is not only a great saving of expense in the construction, but is a material convenience where room is limited. The calculations on the cost of light from oilgas are taken on the usual price of good whaleoil; but, it is to be observed, that cheaper oils will answer the purpose nearly as well, and many of these are often to be procured; and the whole expense may be materially lessened by their use.

In the course of their first experiments, Messrs. John and Philip Taylor were surprised to find that the apparatus they employed gradually lost its power of decomposing oil, and generating gas. On investigation, they discovered that the metallic retorts, which had originally decomposed oil and produced gas in abundance, ceased in a very great degree to possess this power, although no visible change had taken place in them. The most perfect cleaning of the interior of the retort did not restore the effect, and some alteration appears to be produced on the iron by the action of the oil, at a high temperature.

Fortunately the experiments on this subject led to a most favorable result, for it was found that, by introducing fragments of brick into the retort, a great increase of the decomposing power was obtained, and the apparatus has been much improved by a circumstance, which, at one time, appeared to threaten its success. A small portion of the oil introduced into the retort, still passed off undecomposed; and, being changed into a volatile oil, it carried with it a great portion of caloric, which rendered the construction of the apparatus more difficult than was at first anticipated; but, by the present arrangement of its parts, this difficulty is fully provided for, and the volatilised oil is made to return into the oilreceiver, whence it again passes into the retort; so that a total conversion of the whole into gas is accomplished without trouble, or the escape of any unpleasant smell.

The only residuum in the retort is a small quantity of carbon, and the only products besides the gas are a minute quantity of sebacic and acetic acids, and a portion of water, all which are easily separated by passing the gas through a vessel containing water.

The superiority of the light from oil-gas over other artificial lights, is fully shown by its rendering the delicate shades of yellow and green nearly as distinct as when viewed by solar light.

Mr. De Ville of the Strand, who has made many important experiments and observations on gas illumination, with a view of applying it to light-houses, is inclined to estimate the average produce in gas of a gallon of oil, at eighty cubical feet. A single jet burner, giving the light of two candles and a half, consumes half a cubical foot of gas per hour. A double jet consumes three quarters of a foot to give twice the above light, and a treble jet requires one foot. The light of an Argand burner of coal-gas, com

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The holes being of the same dimensions in each lurner.

Various statements have been given of the illuminating power of oil and coal-gas; nor is this to be wondered at, when we considerthat the quality of the gases depends so much on the mode of preparation, and take into account also the defective modes usually adopted for determining the intensity of the light afforded by their combustion. Mr. Ricardo, in his early papers on this subject, has given a very flattering account of oil gas. He states, that an Argand burner, giving a light equal to six candles, six to a pound, consumed one cubic foot per hour; and, as Mr. Accum mentions, that an Argand of coal-gas, giving a light equal to three candles, eight to the pound, consumes two feet in the same time, he has inferred, supposing the candles of the same size, the illuminating power as 4 to 1; but, taking the average of a number of experiments, he has fixed their comparative power of giving light as 34

to 1.

In these trials, however, the gases were not brought into comparison with each other by burning them together, and the data on which he proceeds seem to be very fallacious, as it is not stated whether the candles were of the same kind in both experiments. Messrs. Taylor and Martineau have, however, come to nearly the same conclusion, that the illuminating power is as 31 to 1, a conclusion drawn from the experiments of Mr. Brande and Mr. Faraday. A gentleman connected with the Liverpool Gas Company, in the answers to the queries put to him by the committee of the Dundee Company, replies, that the relative quantity of gas requisite to supply the same light, is as 14 oil-gas to 51 coal-gas, making their power of affording light rather more than 3 to 1. Though the above statements place the illuminating power of oil-gas so high, a very different account is given by others. According to Mr. Neilson, Glasgow, it is not to be rated at above 2, or at all events beyond 24, to the other as 1; and the same conclusion is drawn from a series of experiments made at Bristol, by Messrs. Herapath and Rootsey, on whose results, Mr. Peckstone has remarked, that every reliance may be placed, as they could not be actuated by party-feeling, but solely by a desire to ascertain the truth. These statements, so very discordant, must arise either from the defective mode of ascertaining the intensity of the light, or from the variable quality of the gas, both of which have had their effect.

The mode usually followed for ascertaining the illuminating power, viz. of producing the

same intensity of shadow, and marking the quantity of the gas consumed in a given time is liable to many objections. It is extremely difficult, for instance, to judge with precision of the depth of shadows; besides, unless each gas is burned under circumstances favorable for producing the greatest light, the conclusion with respect to their power of illumination is not correct. Some of the experiments in which the oilgas is stated as 3 to 1, it has beer. said, were conducted by using burners of equal dimensions for both now, it is well known that the former requires a smaller one than the latter, otherwise the intensity of the light is not in proportion to the gas consumed, part of it probably escaping combustion. The remark, with respect to the variable quality of the gas, is also of equal force. In a paper published by Mr. Dewey, in the Annals of Philosophy, some experiments on the illuminating power of the gases are stated, with a view of setting the matter at rest.' This we conceive they have done, as far as can be expected; but we suspect the conclusion to be drawn from them, is very different from that at which Mr. Dewey arrives. The gases were taken from main-pipes running parallel to each other, the coal-gas from the Imperial Gas Works, the other from that at Bow. Being burned so as to afford the same intensity of light, the quantities were found by accurate metres to be (taking the mean of seven trials) as 4850 to 1368, very nearly 3}} to 1. It has been supposed by some, that the specific gravity of coal-gas is a good test of its purity, the lighter it is, the greater being its power of illumination. The experiments of Dr. Henry, and others, however, disprove this; indeed, after the gases are properly purified, the heavier they are, so much the more will be the light afforded by their combustion. The gas used by Mr. Dewey was of specific gravity 406, now this was less than pure carbureted hydrogen, which is 555. In a note to the same paper, the editor remarks, that the results of Mr. Dewey coincide with those obtained by him and Mr. Faraday. The coal-gas they subjected to trial was, in one instance, of specific gravity 429, in another, 406. The oil-gas was ·965 and '939, and their illuminating power to the former was as 3 to 1. As the coal-gas in all of these experiments was of inferior specific gravity to carbureted hydrogen, we may reasonably infer, that they contained a considerable proportion of pure hydrogen, which, it is well known, affords a very feeble light. Dr. Henry has found the gas to vary in specific gravity from 345 to. 650, its illuminating power increasing as it approached the maximum. The specific gravity of the coal-gas of Edinburgh, which is allowed by all to be of very superior quality, has been found to be so high as 680. The oil-gas used by Mr. Dewey was 939. Dr. Henry mentions, that in some of his experiments it was '906. Dr. Fyfe found that from the small apparatus of Mr. Milne (Taylor and Martineau's), to be ·940, and which is generally allowed to be very fine, so that we take it for granted, that that of Mr. Dewey was of good quality. If then, in these trials, a good oil-gas, pitched against a very inferior coal-gas, is only as 3 to 1, the illuminat

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ing power of the former must be much reduced when brought in competition with the latter when of equally good quality; consequently, it must be far short of that stated by Mr. Dewey.

Dr. Henry, in his paper on the nature of the gases produced by the decomposition of coal and oil, proposes to ascertain their illuminating power by finding the quantity of oxygen necesssry for their combustion; for, according to him, the more a gas will consume, the more light it will afford. He has found, that oil and coal gas, produced under different circumstances, take different quantities of oxygen.

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Hyd.

Ox.

Hydrog. Total.

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From the above tables it would, of course, be inferred, that the illuminating power of oil-gas, No. 4, is the greatest; that of coal-gas, No. 1, the least, these being to each other as 260 to 78; that is, as 34 to 1. From this, then, it appears, that the best oil-gas is to the worst coal-gas as 3 to 1; of course a very different conclusion with respect to their illuminating power would be drawn, were we to take an average from the above tables, by which we should diminish the light given out by the former, and increase that from the latter.

The gaseous matter, given off from coal and oil, now known by the name of coal and oil gas, contains nearly the same ingredients, but in different proportions. Dr. Henry has shown, that they are mixtures of hydrogen, carbonic oxide, carbureted hydrogen, and olefiant gas, with occasionally a little nitrogen; and, in addition to these, coal-gas, before it is subjected to the process of purification, always contains ammonia, carbonic acid, and sulphureted hydrogen; but from which it is, or at least ought to be, freed before it is sent into the gas-holder; so that both gases, when exposed for sale, contain the same ingredients, but in different proportions. There is also given off, during the decomposition of coal and oil, an essential oil, which seems to be held in solution, in a state of vapor, in the gas, and,which is the cause of the smell, and, as some suppose, adds to the illuminating power.

Dr. Henry, in his paper in the Annals of Philosophy for September 1821, has given the component parts of different samples of gas. The coal-gas was prepared from Wigan Canal, at the manufactory of Messrs. Phillips and Lee, and collected from an opening in a pipe between the retort and the tar-pit, generally about half an hour after the commencement of the distillation, except in the instance of the gas No. 4, which was taken five hours, and, No. 5, ten hours from that period; the carbonic acid and sulphureted hydrogen being removed by washing it with solution of potassa.

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The gas condensed by chlorine is supposed to be partly olefiant, and partly a volatile oil. That not condensed, the above tables show to vary in its composition. In the best specimen of oil-gas, the carbonic oxide is in larger proportion than in the best kinds of coal-gas; and the carbureted hydrogen is most abundant in the latter. The hydrogen in both appears to increase as the temperature at which they are formed becomes higher, and is always greatest in the last proportions.

It has been proposed in Holland to substitute turf for coal, or oil, as a material from which to obtain a gas for illumination. The experiments that have been made promise much success; and the apparatus required may be of far simpler

construction than those used in the distillation of coal. The products do not require that careful and elaborate process of purification which is necessary for the gas from coal. It is said also that the light is better. The light may be better than that from coal-gas badly made, or carelessly used; but it is not likely that, with equal precautions, the first should surpass, or even equal the latter. With reference to the arrangement of the pipes, by which gas is distributed for the purpose of illuminating cities, it may be proper to state that all gas mains laid in public streets should be placed at least eighteen inches below the surface of the ground, to secure them from being disturbed by carriages, or interfering with the paving of the street; they should be placed perfectly firm, so that they may not easily give way. The course of the pipes should be rectilinear, with a dip of about one inch in every ten feet distance.

In all wide streets, where the number of houses on both sides of the streets, to be supplied with gas, is numerous, it is more economical to employ a separate gas main for each side of the street, than to make use of one larger main for both sides; because smaller mains may then be employed, and the collateral branch pipes leading into the houses are shorter; these circumstances amply compensate for the additional main. All branch pipes proceeding from a main should have a dip of about one inch in ten feet, towards the main from which they proceed, so that any fluid that may happen to collect in these pipes must run into the mains. All small wrought-iron branch pipes proceeding from the mains into the houses, or places to be lighted with gas, should be covered with a thick coat of coal tar, before they are laid down into the ground; this may easily be done by heating the pipe, and laying on the boiled tar with a brush. Every separate length of branch pipe should be tried by condensing the gas in the pipe under water, in order to be certain that it is sound. The junctures of these pipes should be made by dipping the male screw of the pipe into a mixture of white lead and linseed oil, before they are screwed together.

Notwithstanding the usual care which can be taken in proving pipes, before the gas is admitted into them, a slight leakage may be sometimes subsequently detected.

Therefore, before the gas is suffered to enter the mains, they should be again proved, in order to be certain that all the junctures are air-tight. The most convenient manner of proving the mains when laid, is by means of a small portable gas-holder filled with common air, and connected, by means of a small pipe, with the system of the mains, to be tried. This gas-holder should be made to act with a pressure at least four times greater than the pressure which the pipes will have to sustain by the gas they are to convey. If the mains are air-tight, the gas-holder will remain stationary; but, if they are not sound, the gas-holder will descend in proportion to the leak of the mains; the quantity of gas lost may be thus ascertained.

In order to guard against the danger of water entering from the external surface into the pipes,

a reservoir should always be placed at the lowest point, where two or more descending mains meet and form an angle, so as to receive the water that may happen to collect at this angular point, an accumulation of which would cut off the communication between the two pipes: this reservoir is usually called a syphon. It ought to be at least twice the diameter of the bore of the mains, between which it is interposed, and four times that diameter in depth. These reservoirs afford the best indication to show the sound or leaky state of the system of the mains. In all instances, where the pipes are perfectly sound, observation has shown, that half a mile of gas-mains, three inches in the bore, does not deposit more than a quart of water in a year; on the other hand, if the mains are leaky, the water of the reservoir requires to be pumped out, sometimes as frequently as every fortnight; and, during wet weather, much oftener. The loss of gas by such leakage is much greater than is generally imagined. Instances might be mentioned where, in order to keep the common air out of a system of faulty pipes, a constant influx of gas, which a pipe two inches in diameter can supply, has been found necessary and this, of course, is just so much gas lost to the economy of the establishment.

With regard to the diameter of the mains, no general rule can be given. it must vary according to the number of branch-pipes and lamps which the main has to supply within a given distance, the angular direction of the mains,-the pressure of the gas-holder,—and, above all, with the relative altitude of the place where the gas-holder is situated, and the place at which the gas is to be supplied, or where the lamps are placed. Indeed, this is one of the most important considerations with regard to the economical distribution of gas-mains; and, by attending to this circumstance, a prodigious saving may be effected.

In order that the pipes for conveying the gas from the mains, and distributing it through the houses or other buildings to be lighted with gas, may, in the first place, not be unnecessarily large, or too small, the following rule may serve as a guide to workmen :

One gas-lamp, consuming four cubic feet of gas in an hour, if situated twenty feet distance from the main which supplies the gas, requires a tube not less than a quarter of an inch in the bore.

Two lamps, thirty feet distance from the main, require a tube three-eighths of an inch in the bore.

Three lamps, thirty feet distance from the main, require a tube three-eighths of an inch in the bore.

Four lamps, forty feet distance from the main, require a tube half an inch in the bore. Six lamps, fifty feet distance from the main, require a tube five-eighths of an inch in the bore.

Ten lamps, 100 feet distance from the main, require a tube three-quarters of an inch in the

bore.

Fifteen lamps, 130 feet distance from the main, require a tube one inch in the bore.

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