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 candle 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, but the spirit still ascending blew up the bladder. 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 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 twenty-four 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 Watts' 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. Philips 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, with many adjacent buildings, were illuminated with coal gas to the exclusion of lamps, candles, and other sources of artificial light. Nearly a thousand 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, 201. and the interest of capital sunk, with due allowance for accidents and repairs, 5501. From the joint amount of these items, must be deducted the value of seventy tons of coke, at 1s. 4d. per cwt. amounting to 931. which reduces the total annual expense to 6021.; 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 favour with the work people; and it being free from the inconvenience 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 favourable. He said, it gave no disagreeable smell; and when questioned as to the purity and goodness 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 entertained 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.

To prove that gas is economically applicable upon a small as well as a large scale, reference might be made to Mr. Cook's statement in the Phil. Mag. Dec. 1808, which, with some other amusing particulars, is noticed in the Edinburgh Review, vol. XIII. page 477.

I have thought it right to state these particulars concerning the earliest trials of gas lights: and now, without adducing further evidence from those remote sources, shall proceed to information gained at the establishments lately instituted in the metropolis; and to that afforded by my own experiments. The apparatus required for gas illumination, consists of retorts for the distillation of the coal, of condensers for the reception of the tar and ammoniacal liquor, of purifiers containing cream of lime, through which the gas passes, and is freed from carbonic acid and sulphuretted hydrogen; of gasometers or reservoirs with their main conduit pipes, and of the burners with their tubes and stop-cocks. Of the construction and expense of the whole of this apparatus, a tolerably correct estimate may be formed by consulting Mr. Accum's "Practical Treatise on Gas Light."

We are indebted to Dr. Henry, of Manchester, for some valuable researches, concerning the composition of the aeriform products of several varieties of coal. (Phil. Trans. 1808.) He has pointed out the various composition of the gas at different periods of the distillation, and has shewn 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 has lately 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, we find that 4 lib. 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

The carbonic acid and sulphuretted hydrogen are separated by the lime in the purifiers.

The same quantity of coal introduced into the cold retort and gradually heated, afforded only twenty-two cubic feet of gas, consisting of

5 Olefiant gas

70 Carburetted hydrogen

18 Carbonate oxide and hydrogen

6 Carbonic acid

1 Sulphuretted hydrogen

100

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 illumination 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 improvement 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 of a chaldron of the best Newcastle coals is 31. The value of the products of its distillation is as follows:

20,000 cubic feet of gas, at 15s. per 1,000 cub. feet, 15

0 0

1.17 17 9

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 five and twenty chaldrons submitted to distillation, and the expense incurred by wear and tear, with the wages of the labourers, 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. 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 Cannell 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