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ing a due supply of air, within and without, nerating gas on a large scale. Fig. 1, plate I. burns very beautifully when a proper glass is Gas Ligut, exhibits a longitudinal section, and placed over the burner. These burners, when fig. 1. shows the front elevation of the oven, very carefully regulated, consume about three built about ten feet above the ground, upon cubical feet of gas per hour, and give light equal piers or arches, which saves brick-work, and to that of six wax candles; but it is requisite, on allows a stage or platform to be erected in front account of carelessness and inismanagement, to of the fire places of the ovens. Between the allow four cubical feet to each burner per hour. back part of the ovens and the wall of the buildThe bat's wing hurner should not consume more ing in which they are erected is left an empty than three cubic feet


space of a few inches to prevent the beat of the Besides the different varieties of coal, some of oven being communicated to the wall. which, as has been hinted, are much preferable The whole interior of the oven, as well as the In others, and coal tar, a useful gas may be horizontal flue which passes underneath the procured from a variety of other substances; and crown of it, near the upper tier of retorts, is lined in the laboratory of the Royal Institution, the with fire-bricks. The uppermost part or crown retort is often fed with waste paper, saw-dust, of the arch is constructed of large fire-bricks, of pieces of wood, &c., and the gas is consumed for such a shape as will allow to flatten the upper a variety of purposes where oil was formerly part of the arch as much as possible, in order to employed.

contract the space between the two upper retorts The following are the results of some experi- and the crown of the arch of the oven. ments upon these subjects, compared with the R, R, fig. 2 and 3, are cylindrical retorts, produce from coal.

placed horizontally in the oven, the lower series 1. The retort was charged with four pounds of are either supported by a large fire-brick, placed coal. The quantity of gas amounted, after hav- edgeways underneath the retort, or by means of ug passed the purifiers, to twenty cubic feet. a stout wrought iron pillar, as shown in the deThe coke remaining in the retort weighed sign. The two upper retorts are supported by 2 lb. 8.7 ozs.

wrought iron straps, T, T, T. The straps pass The heating power of the gas flame was com- through the brick-work of the upper part of the pared with that of a wax candle, by ascertaining oven, as shown in the designs, and they are sethe time required by each to raise two ounces of cured with screws and nuts to an iron bearing water, in a thin copper vessel, from 55° to 212°. bar, the extremities of which are supported by The flames were made as similar in dimensions the outer walls of the oven. Each retort is furas possible, and so placed that their joints just nished at the extremity opposite to the mouthtoriched the bottom of the vessel. The heating piece with a short projecting piece or tail let power of the candle being assumed as = 1, that into the brick-work of the oven. of the coal gas flame was = 1.5.

M, fig. 4, shows the mouth-piece of the retort 2. Four pounds of the dried wood of the com- with its cross bar and hand screw; and fig. 5 mon willow yielded sixteen cubical feet of gas, shows the mouth-piece drawn to a larger scale. and fourteen ounces of charcoal remained in the E is the band-screw, with its cross or bearing retort. The gas burned with a very pale blue bar D, which passes through the projecting arms flame, and was unfit for the purpose of illumi- C, C. The lid of the mouth-piece has a conical nation, and contained no olefiant gas.

edge, so that it fits close when put into its place 3. Four pounds of the wood of the mountain by means of the hand-screw E. ash afforded fifteen cubical feet and a half of F, fig. 6, is the fire-place, with the ash-pit E of gas, and thirteen ounces and a half of charcoal. the oven. The door of the ash-pit is provided The fame was very pale and blue.

with three slits covered within by a register slide, 4. Four pounds of white' birch wood gave to regulate the admission of air as occasion may fourteen cubical feet of gas, and twelve ounces require. The fire passes freely and uniformly of charcoal. The fame similar to 2 and 3. round all the retorts, and the whole cavity of the

5. Four pounds of hazel wood yielded thir- oven acquires an equable temperature, which it teen cubical feet and a half of gas, and twelve retains, if the workman takes care to admit as ounces and a half of charcoal. Its heating power little air as possible through the register door of was = 1-2. It burned with a better flame than the ash-pit

, when the upper part of the arch, or 2, 3, and 4, but the intensity was not sufficient crown of the oven has acquired a bright cherry for any useful purpose of illumination.

red heat. The liquid substances, namely the tar 6. Four pounds of writing paper gave eigh- and ammoniacal Auid, collect in the hydraulic, teen cubical feet of gas, and the remaining char- main H, which is furnished with a perpendicucoal, which beautifully retained the form and lar diaphragm or partition plate to cause a certexture of the paper, weighed eleven ounces and tain quantity of the liquid deposited in it to aca half. The heating power of the gas was = 1.6. cumulate to a certain height, and thus to seal the It burned with a fame nearly approaching in perpendicular pipe P. The liquid cannot filow illuminating power to that of coal gas.

out of the horizontal pipe H, till it rises to the These experiments, along with others which level of the diaphragm. it is thought unnecessary to notice, prove that K, fig. 7, is the discharging pipe, connected the gas from woods is not fit for the purposes of with the upper part of the horizontal main H: illumination, although, as evolved during the it serves to convey away the gaseous and liquid production of charcoal, it may conveniently be products from the hydraulic main H. By means consumed in the laboratory as a source of heat. of this pipe the tar and ammoniacal fluids are We may now describe the retort oven for ge- coveyed into any convenient reservoir, called

the tar cistern, which is perfectly air-tight, and stated the quantity from Newcastle coal to be the from this vessel the liquid may be drawn off by same, four feet and a half per pound. Mr. Dewy, means of a pipe or stop-cock. The extremity in a paper in the Annals of Philosophy, asserts, of the pipe which communicates with the liquid that at Liverpool, Mr. King considers it good is bent downwards, so that no air can enter the economy to procure 7000 feet from a ton of vessel.

Wigan Orral coal, making it only 700 feet from It is essential that the condensation of the 2 cwt., a very little more than three feet per vaporous fluids should be fully completed before pound. He has stated also, that, at Glasgow, they reach the tar vessel. To effect this, there is i200 feet are procured from cwt. of cannelusually allowed a considerable distance to inter- coal, which is considerably above that mentioned vene between the discharging pipe, K, and the by Mr. Neilson. From these various statements, reservoir destined to receive the condensable the general conclusion has been drawn, that 2 products; or the pipe is made to pass through cwt. of good coal ought to yield about 1000 feet a vessel containing water, called the condenser, of gas. which acts in a similar manner as the refrigeratory With respect to the quantity to be obtained of a common still. It is obvious that it is imma- from oil, this must, of course, also depend on the terial how the condensation of the

vaporous fluid nature of the oil, and the manner of decomposing is effected; it is essential, however, that the con- it. Mr. Ricardo mentions, that, from repeated trials densation should be complete before the liquid in various oil-gas establishments, it has been tar and ammoniacal fluid reach the reservoir ascertained that one gallon produces 100 cubic feet. destined to receive these products. The gaseous From the experiments of Mr. Brande, and Mr. fluid, which accompanies the condensable pro- Faraday, it appears that the same quantity affords ducts, is then made to pass into the lime ma- from 100 to 1io feet. In some instances it has chine, in order to be deprived, by means of been known to amount to about 120; but in these quicklime and water, of the portion of sul- cases, it was not good, the additional quantity phureted hydrogen and carbonic acid gas which having been derived from substances put into the was combined with the gas. And, when this retort. At Leith, a gallon of whale oil affords has been accomplished, the purified gas is con- from ninety-eight to 108 cubic feet; and the same veyed into the gas-holder, where it is stored up quantity of palm-oil, from ninety-seven to 114. for use.

In some establishments, the hydraulic It may be considered a fair estimate to obtain main is furnished with two discharging pipes; 100 feet from each gallon, presuming, of course, the one carries away the condensable fluid, into that the oil is decomposed under the most favorwhich the perpendicular pipes, P, fig. 8, dip, able circumstances, so as to get a gas possessing whilst the other serves to convey away the gaseous the greatest illuminating power; for on this every fluids to a condenser, in order to deposit the thing depends. From experiments performed on vaporous portion of condensable liquid it may a small scale, and from trials made at Leith, Dr. contain, and from thence the gas passes into the Fyfe found that if the oil be allowed to flow into purifying apparatus, or lime machine. X, fig. 9, a retort brought just to a red heat, there is comis a small screw plug, which, when opened, re- paratively little gas, but a great deal of volatile stores the equilibrium of the air within and oil. When the retort is brought to an intense without the retort previous to the lid being taken heat, lamp-black is formed in considerable quanoff, to prevent the loud report which otherwise tity; so that, in both of these ways, there is a happens when the lid or cover of the retort is great loss. When the retort is at a full red heat, suddenly removed. To avoid these explosive the oil seems to undergo decomposition most reports, which had become a nuisance to the easily, and to give off the largest proportion neighbourhood of gas works, the practice of of good gas. gradually withdrawing the lid of the retort, and, In conducting the decomposition of coal, the at the same time, presenting a lighted torch, has evolution of the gas is far from being, with regard been adopted at some works, which fully reme- to quantity, uniform, during different periods of dies the evil.

the distillatory process. The formation of the The quantity of gas to be obtained from coal gas is more rapid in the beginning of the process, varies according to the coal employed and the man- and gradually slackens as the operation proceeds. ner in which it is treated : the quality also depends The gas also differs in its chemical constitution, on the mode of applying the heat. Taking it at different periods of the process; although, in for granted that the most advantageous method the case of large supplies, this difference is of of decomposing it is followed, the quantity from little consequence after the gas is purified in the the different kinds of coal varies. In stating the usual manner. The former consideration, howproportions, therefore, we can come only at an ever, has given rise to various modes of operating, average conclusion.

of which it will be proper to take some notice. Mr. Peckston, in his work on Coal-gas, states, It must be obvious that, in proportion as the that a chaldron of Newcastle Wall's End coal will mass of coal in the retort becomes carbonised or yield 10,000 feet, supposing it decomposed under converted into coke, the exterior surface becomes the most advantageous circumstances; 2 cwt. a gradually increasing obstacle to the action of will, therefore, yield about 750 feet. At Edin- the heat upon the interior or central part of the burgh, 2 cwt. of Parrot-coal yield, on an average, coal remaining to be decomposed. The heat 860 feet of gas. According to Mr. Neilson, required on that account must be more intense, engineer, Glasgow, 2 cwt. of Lesmahago coal will and kept up to purpose ; and the extrication of produce 1008 cubic feet of gas, allowing four and gas becomes slower and slower, as the open a half each pound. Mr. Russell, of London, has ration proceeds. The loss occasioned by this

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rapid diminution of the means employed, is operation, for the evolution of 115 cubic feet of serious in every point of view, in regard both gas, is required in the eighth hour for the proto the quantity of fuel used and time wasted, but duction of no more than forty-two cubic feet, being it is unavoidable in the operation of decomposing a decrease in effect of nearly two-thirds. coal in masses or layers from five to ten inches When larger retorts are employed for decomin thickness, and must be a great drawback on posing coal, in masses from five to ten inches in the value of the gas-light discovery. The loss of thickness, the loss of heat is in a much greater fuel, it is obvious, must be just in proportion to ratio. the quantity of carbonised matter, or coke, which In the hope of remedying, in some measure, is kept hot to no purpose, awaiting the decom- the evils thus distinctly ascertained to arise from position of that portion of coal which it is the very the undue thickness of the masses of coal submeans of protecting from becoming undecom- jected to the distillatory process, there have not posed.

been wanting manufacturers who have had reA striking exemplification of this statement course to experiments on a large scale, to ascerwill be seen in the following table, exhibiting tain with certainty whether they might not be the result of the progressive produce of coal gas, gainers by suffering the distillatory process, when obtainable, in a given time, by means of cylin- the retorts are charged with two bushels of coal, drical and parallelopiped retorts.

to proceed only for the space of six hours, instead Experiment with one Cylindrical Retort, con

of eight. But the result of these experiments taining two bushels of coal.

has shown satisfactorily, that it is more profitable Hours of the distil.

Quantity of gas

to keep up the distillatory process for a period of latory process.

eight hours, with the retorts fully charged, than

produced. First hour

115 cubic feet.

to abridge the operation by terminating it at the

end of six hours. Others, again, have imagined, Second hour

81 Third hour

that it would be more economical to decompose

78 Fourth hour


a less quantity of coal at once, or to decrease the Fifth hour

thickness of the stratum of coal in the cylindrical

66 Sixth hour


or in any of the before-named retorts; but then, Seventh hour


again, serious difficulties occur in the practice. Eighth hour


The more frequent charging of the retorts and

luting on the covers, which such a mode of 555

operating requires, occasions a prodigious waste The quantity of gas is at the rate of 10,000 cubic of fuel, time, and labor. A greater number of feet to the chaldron (27 cwt.) of coal.

retorts, and more workmen, must likewise be

employed, in order to produce the requisite Experiment with eighteen Cylindrical Retorts, quantity of gas daily, which the manufacturer containing one chaldron of coal.

is called upon to supply; more space of ground Hours of the distil

Quantity of gas is required, and more dead capital must be sunk latory process.

produced. in the establishment. The more frequent and First hour

2000 cubic feet. sudden alterations of temperature which the Second hour


retorts necessarily suffer, by the more frequent Third hour


introduction of cold coal, renders them extremely Fourth hour


liable to become injured ; and it is almost imFifth hour


possible to maintain a number of retorts, thus Sixth hour


worked, at a uniform temperature. Seventh hour


One of the best purposes to which the tar proEighth hour.


duced in the distillation of coal can be applied,

is to the production of gas, which yields in the 9985

proportion of about eighteen cubic feet from each This experiment was made with retorts set on pound, and of an excellent quality for illumithe flue plan.

nation. The following is an account of Mr. The coal employed was (Bewick and Craister's Clegg's apparatus for its decomposition, and Wall's End) Newcastle coal.

which appears to answer better than any yet Experiment with thirty-six Parallelopipedal devised :Retorts, each containing two bushels of coal. A, plate I., fig. 10, is a tar cistern. B, a cock Hours of the disti).

Quantity of gas

by which it is drawn off. As a sufficiently small latory process.

produced. stream of tar is apt to stop, by its stiffness, a First hour.

4.058 larger quantity than is wanted is allowed to run Second hour

3:028 into E, upon the edge of the dividing plate C, Third hour

2.871 adjusted by the screw D: the excess rups off by Fourth hour

2.526 a waste pipe into any proper vessel, while a due Fifth hour

2:380 portion trickles through E into F, and runs Sixth hour

1.971 down G, G, into H, where, when the tar has Seventh hour

1.754 reached the level I, it is conducted into the retort Eighth hour

1.450 K, L, M, the return of gas being prevented by

the immersion of the end of the tube G, G, into

20.038 the tar in the vessel H. The retort, resembling The same heat, as we have seen from the first a bent pipe or syphon, is so inserted in a proper lable, which is necessary during the hour of Aue, that the ends K, M, provided with lids or


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