GAS. Goth. and Swed. gasa, to ferment, a term first commonly used by Van Helmont for fluids of an aeriform character.

GAS. The various gaseous bodies have been enumerated, and their properties explained, in that department of chemistry, to which they peculiarly belong; and we now propose to direct the attention of our readers to one of the most important practical applications of gaseous chemistry, in the illumination of buildings, and even large cities, by carbureted hydrogen gas.

The producing from coal an aeriform fluid, which could be distributed at pleasure in every direction, for the purpose of economical illumination, has justly been ranked amongst the greatest benefits which the science and enterprise of this country have conferred on mankind.

That coal evolves a permanently elastic and inflammable aëriform fluid, seems first to have been experimentally ascertained by the Rev. Dr. Clayton, and a brief account of his discovery is published in the Philosophical Transactions for the year 1739. The following is an extract from his paper: I got some coal, and distilled it in a retort in an open fire. At first there came over only phlegm, afterwards a black oil, and then likewise a spirit arose, which I could no ways condense; but it forced my lute or broke my glasses. Once when it had forced my lute, coming close thereto, in order to try to repair it, I observed that the spirit which issued from it caught fire at the flame of the candle, and continued burning with violence, as it issued out in a stream, which I blew out and lighted again alternately for several times. I then had a mind to try if I could save any of this spirit, in order to which, I took a turbinated receiver, and putting a candie to the pipe of the receiver, whilst the spirit arose, I observed that it catched flame, and continued burning at the end of the pipe, though you could not discern what fed the flame. I then blew it out, and lighted it again several times; after which I fixed a bladder, squeezed and void of air, to the pipe of the receiver. The oil and phlegm descended into the receiver, hut the spirit, still ascending, blew up the bladJer. I then filled a good many bladders therewith, and might have filled an inconceivable number more, for the spirit continued to rise for several hours, and filled the bladders almost as fast as a man could have blown them with his mouth; and yet the quantity of coals distilled was inconsiderable.

I kept this spirit in the bladders a considerable time, and endeavoured several ways to condense it, but in vain. And when I had a mind to divert strangers or friends, I have frequently taken one of these bladders, and pricking a hole therein with a pin, and compressing

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gently the bladder near the flame of a candle till it once took fire, it would then continue flaming till all the spirit was compressed out of the bladder, which was the more surprising, because no one could discern any difference in the appearance between these bladders, and those which are filled with common air.

But then I found that this spirit must be kept in good thick bladders, as in those of an ox, or the like; for if I filled calves' bladders therewith, it would lose its inflammability in twentyfour hours, though the bladders became not relaxed at all.'

But the application of the gas thus generated to the purposes of economical illumination is of much more recent date, and the merit of introducing it is principally due to Mr. Murdoch, whose observations upon the subject are published in the Philosophical Transactions for 1808. He first tried it in Cornwall, in the year 1792; and afterwards, in 1798, established an apparatus upon a more extended scale at Boulton and Watt's foundry at Birmingham; and it was there that the first public display of gas lights was made in 1802, upon the occasion of the rejoicings for peace. These, however, were but imperfect trials, when compared with that made in 1805 at Messrs. Phillips and Lee's cotton mills at Manchester; and upon the results of which, all subsequent procedures, with regard to gas lighting, may be said to be founded. The whole cotton mill, and many adjacent buildings, were illuminated with coal gas, to the exclusion of lamps, candles, and other sources of artificial light. Nearly 1000 burners of different forms were employed; and the light produced was estimated equal to that of 2500 well managed candles of six to the pound.

The most important and curious part of Mr. Murdoch's statement relates to the cost of the two modes of lighting (namely, by gas and candles) per annum. The cost of the coal, used to furnish the gas, amounting annually to 110 tons, was £125. Forty tons of coals to heat the retort £20, and the interest of capital sunk, with due allowance for accidents and repairs, £550. From the joint amount of these items must be deducted the value of seventy tons of coke, at 1s. 4d. per cwt., amounting to £93, which reduces the total annual expense to £602; while that of candles to give the same light would amount to £2000.

Such was the flattering result of the first trial of gas illumination upon a tolerably extensive scale. In regard to its efficacy, we are informed by Mr. Murdoch, that the peculiar softness and clearness of the light, with its almost unvarying intensity, brought it into great favor with the work people; and its being free from the incon

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venience of sparks, and the frequent necessity of snuffing, are circumstances of material importance, as tending to diminish the hazard from fire, to which cotton mills are so much exposed. When Mr. Lee was examined by Mr. Brougham, in 1809, before a committee of the house of commons, against the Gas-light and Coke Company's bill, his evidence was then equally favorable. He said, it gave no disagree able smell; and when questioned as to the goodness and purity of the light, I burn it,' said he, every night in my own house, instead of thirty pairs of candles.' He further added, that he found it perfectly wholesome, and that it was never complained of either in his own dwelling-house, or in the mill.

The president and council of the Royal Society proved the high opinion which they enter tained of the value and importance of Mr. Murdoch's communication, on the employment of the gas from coal for the purpose of illumination, by adjudging to him count Rumford's gold and silver medals.

We are indebted to Dr. Henry, of Manchester, for some valuable researches concerning the composition of the aëriform products of several varieties of coal. He has pointed out the various composition of the gas at different periods of the distillation, and has shown the important influence of the circumstances under which the coal is distilled, upon the proportion of gas yielded, and its fitness for the purposes of illumination. This fact attracted the notice of Mr. Clegg, the engineer of the Gas-light Company, who has founded upon it several ingenious improvements in the construction of the retorts employed at the Westminster gas works. Coal in large heaps, and gradually heated, affords less gas, and more water and tar, than when it is extended over a considerable surface, and suddenly brought to a red heat. It is also very advantageous to dry the coal before its introduction into the retort.

In a small gas apparatus, erected in the laboratory of the Royal Institution, it was found that 4 lbs. of good Newcastle coal, introduced into the retort previously heated red in a shallow iron pan, may be made to afford a produce of from twenty to twenty-six cubic feet of gas, consisting of

8 Olefiant gas.

72 Carbureted hydrogen.

13 Carbonic oxide and hydrogen. 4 Carbonic acid.

3 Sulphureted hydrogen.

The specific gravity of the former gas, that of air being 1000, was 560, and of the latter 555: the fitness of gases for the purposes of illuminating is, generally speaking, directly as their specific gravity.

These experiments lead to the conclusion, that a chaldron of good Wallsend Newcastle coals would afford from 17,000 to 20,000 cubical feet of gas, but the process of distillation, as now carried on in the large establishments for lighting the metropolis, seldom affords a larger average produce than 12,000 cubical feet. There can, however, be little doubt that, by improvements in the construction and management of the retorts, the highest of the above averages might be procured; and calculating upon this produce of gas, and upon the other substances yielded by the operation, we obtain a curious and striking result.

The average value in London of a chaldron of the best Newcastle coals is £3. The value of the products of its distillation is as follows:

From the value of products must, of course, be deducted, the value of the common coal employed in the furnaces for heating the retorts, amounting to about five chaldrons for every fiveand-twenty chaldrons submitted to distillation, and the expense incurred by wear and tear, with the wages of the laborers, and lastly, the interest upon capital. Mr. Murdoch's estimate, already quoted, will be found pretty accurate upon these heads.

The tar is frequently employed for the production of gas, either by mixing it with small coal in the retorts, or by passing it through a red hot tube. Every pound yields between seventeen and eighteen cubic feet, containing from fifteen to twenty per cent. of olefiant gas. When, therefore, it has been cleansed by lime, it burns with a very brilliant flame, and is a most improving addition to the common gas. Wigan and Cannel coal yield the best and largest proportion of gas for the purposes of illumination, but it is seldom it can be employed on account of its high price.

The burners, or tubes whence the gas issues for combustion, may be infinitely and tastefully varied. The varieties commonly employed are the bat's-wing burner, and the Argand burner. The former consists of a brass tube having a slit at its extremity about a quarter of an inch long and one-fortieth of an inch wide. The latter is composed of two concentric brass tubes, about two inches long, closed at bottom by a ring of brass, and at the top by one of steel, perforated with sixteen or eighteen holes, of one-thirtieth of an inch in diameter. The gas enters the cavity between the tubes, and issues from the circular row of apertures, where it is inflamed, and hav

ing a due supply of air, within and without, burns very beautifully when a proper glass is placed over the burner. These burners, when very carefully regulated, consume about three cubical feet of gas per hour, and give light equal to that of six wax candles; but it is requisite, on account of carelessness and mismanagement, to allow four cubical feet to each burner per hour, The bat's wing burner should not consume more than three cubic feet per hour.

Besides the different varieties of coal, some of which, as has been hinted, are much preferable to others, and coal tar, a useful gas may be procured from a variety of other substances; and in the laboratory of the Royal Institution, the retort is often fed with waste paper, saw-dust, pieces of wood, &c., and the gas is consumed for a variety of purposes where oil was formerly employed.

The following are the results of some experiments upon these subjects, compared with the produce from coal.

1. The retort was charged with four pounds of coal. The quantity of gas amounted, after havng passed the purifiers, to twenty cubic feet. The coke remaining in the retort weighed 2 lb. 8-7 ozs.

The heating power of the gas flame was compared with that of a wax candle, by ascertaining the time required by each to raise two ounces of water, in a thin copper vessel, from 55° to 212°. The flames were made as similar in dimensions as possible, and so placed that their joints just touched the bottom of the vessel. The heating power of the candle being assumed as 1, that of the coal gas flame was = 1.5.

2. Four pounds of the dried wood of the common willow yielded sixteen cubical feet of gas, and fourteen ounces of charcoal remained in the retort. The gas burned with a very pale blue flame, and was unfit for the purpose of illumination, and contained no olefiant gas.

3. Four pounds of the wood of the mountain ash afforded fifteen cubical feet and a half of gas, and thirteen ounces and a half of charcoal. The flame was very pale and blue.

4. Four pounds of white birch wood gave fourteen cubical feet of gas, and twelve ounces of charcoal. The flame similar to 2 and 3.

5. Four pounds of hazel wood yielded thirteen cubical feet and a half of gas, and twelve ounces and a half of charcoal. Its heating power was 1.2. It burned with a better flame than 2, 3, and 4, but the intensity was not sufficient for any useful purpose of illumination.

6. Four pounds of writing paper gave eighteen cubical feet of gas, and the remaining charcoal, which beautifully retained the form and texture of the paper, weighed eleven ounces and a half. The heating power of the gas was 16. It burned with a flame nearly approaching in illuminating power to that of coal gas.

These experiments, along with others which it is thought unnecessary to notice, prove that the gas from woods is not fit for the purposes of illumination, although, as evolved during the production of charcoal, it may conveniently be consumed in the laboratory as a source of heat.

We may now describe the retort oven for ge

nerating gas on a large scale. Fig. 1, plate I. GAS LIGHT, exhibits a longitudinal section, and fig. 1. shows the front elevation of the oven, built about ten feet above the ground, upon piers or arches, which saves brick-work, and allows a stage or platform to be erected in front of the fire places of the ovens. Between the back part of the ovens and the wall of the building in which they are erected is left an empty space of a few inches to prevent the heat of the oven being communicated to the wall.

The whole interior of the oven, as well as the horizontal flue which passes underneath the crown of it, near the upper tier of retorts, is lined with fire-bricks. The uppermost part or crown of the arch is constructed of large fire-bricks, of such a shape as will allow to flatten the upper part of the arch as much as possible, in order to contract the space between the two upper retorts and the crown of the arch of the oven.

R, R, fig. 2 and 3, are cylindrical retorts, placed horizontally in the oven, the lower series are either supported by a large fire-brick, placed edgeways underneath the retort, or by means of a stout wrought iron pillar, as shown in the design. The two upper retorts are supported by wrought iron straps, T, T, T. The straps pass through the brick-work of the upper part of the oven, as shown in the designs, and they are secured with screws and nuts to an iron bearing bar, the extremities of which are supported by the outer walls of the oven. Each retort is furnished at the extremity opposite to the mouthpiece with a short projecting piece or tail let into the brick-work of the oven.

M, fig. 4, shows the mouth-piece of the retort with its cross bar and hand screw; and fig. 5 shows the mouth-piece drawn to a larger scale. E is the hand-screw, with its cross or bearing bar D, which passes through the projecting arms C, C. The lid of the mouth-piece has a conical edge, so that it fits close when put into its place by means of the hand-screw E.

F, fig. 6, is the fire-place, with the ash-pit E of the oven. The door of the ash-pit is provided with three slits covered within by a register slide, to regulate the admission of air as occasion may require. The fire passes freely and uniformly round all the retorts, and the whole cavity of the oven acquires an equable temperature, which it retains, if the workman takes care to admit as little air as possible through the register door of the ash-pit, when the upper part of the arch, or crown of the oven has acquired a bright cherry red heat. The liquid substances, namely the tar and ammoniacal fluid, collect in the hydraulic main H, which is furnished with a perpendicular diaphragm or partition plate to cause a certain quantity of the liquid deposited in it to accumulate to a certain height, and thus to seal the perpendicular pipe P. The liquid cannot flow out of the horizontal pipe H, till it rises to the level of the diaphragm.

K, fig. 7, is the discharging pipe, connected with the upper part of the horizontal main H: it serves to convey away the gaseous and liquid products from the hydraulic main H. By means of this pipe the tar and ammoniacal fluids are coveyed into any convenient reservoir, called