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gas; but this not being the case, it is obvious that the supposition cannot be well founded*.

A ton of Lesmahagow coal, when distilled at the usual temperature, yields about (10,080 cubic feet) one-fifth of its weight of gas, two-fifths of coke, and two-fifths of tar, water, &c.

The gas contains about one-fifth of the carbon in the raw coal, two-elevenths of the hydrogen, and two-ninths of the oxygen; about one-half of the carbon remains in the state of coke, so that about twofifths go to the formation of the naphthalin, naphtha, naphthene, naphthol, &c., which are formed during the distillation.

Nine-elevenths of the hydrogen and seven-ninths of the oxygen go to the formation of water and various other compounds. The ammonia formed amounts to about 1 per cent. of the liquor obtained during the distillation of the coal.

When gas-works were first established the coal was distilled in iron retorts, but it has been found more economical to substitute vessels of stoneware, or rather indeed ovens of fire-brick made air-tight; these I believe are generally superseding the iron retorts.

During the course of last winter I made thirty-five analyses of gas from different gas-works, but most commonly Glasgow gas. The gas which I used was taken from a pipe at some distance from the gasworks, because the gas required to be washed and purified before it was examined. After turning the stop-cock the gas was kindled and allowed to burn for several minutes before I began to collect it. In every case it contained a mixture of common air, which varied in different specimens of gas from 4 per cent. to 28 per cent.; the mean quantity was 12 per cent. The specimen containing 28 per cent. of common air was brought up from Greenock, and though very great care was taken in packing it, it is possible that at least a portion of this air might have made its way into the bottles during the transit. If we omit this specimen, the average quantity of common air in the Greenock gas was 10 per cent.; the average quantity in the Glasgow gas was 12 per cent.

I think it most likely that the common air, which forms a constant ingredient in all gas from gas-works that I have examined, had made its way into the pipes, which it must be very difficult to make air-tight; and when the pressure is removed common air will undoubt

Mr. John Hart, of this city, states that he made an experiment which appears to explain the appearance of the hydrogen towards the end of the process. "Having conceived the idea many years ago of causing gas to take up an additional dose of carbon, by passing it over red-hot charcoal, he procured a 14 inch iron pipe, and having charged it with charcoal, he passed it through the furnace below the gas retort, and joined one end with the pipe from the retort and the other to the pipe leading to the condenser; the fire was then applied and the retort charged as usual. After the gas-holder had risen about a foot, he observed the lead pipe leading to the condenser becoming very hot; it soon after gave way and fell to pieces, and the whole of the gas escaped into the air; but it had no longer the yellow silky appearance of gas issuing from a retort; it had become a white vapor, and had also lost the smell. When the charcoal was examined it was found to be covered over with a fine smooth, shining black coat of carbon, which had been deposited on it." Mr. Hart has concluded from this and other facts, that the gas is decomposed by the red-hot coke, and proposes that the coal should be applied in thin layers to the interior surface of the retorts.

edly enter wherever it can find access. The Greenock gas was collected in an apartment very near the gas-works; the Glasgow gas was collected in my laboratory, which may be about a furlong from the gas-works; now the average quantity in the Greenock gas was 104, and in the Glasgow 12}.

The highest specific gravity of the Glasgow gas was 0.582, and the lowest 0-462; the average was 0.503.

The quantity of olefiant gas in Glasgow gas varied from 11.77 per cent. to 17.83 per cent.; the mean quantity was 13.52 per cent.

I got gas made at Greenock with as much care as possible from each of the three varieties of cannel coal found in the neighborhood of Glasgow, namely, Skaterigg, Lesmahagow and Monkland: the specific gravities of these gases were,

Skaterigg.. 0.497

Lesmahagow 0.560

Monkland. . 0.622

The olefiant gas per cent. contained in each was as follows:

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Mr. Ritchie, the manager of the Greenock gas works, who prepared these gases, told me that he thought rather too much heat had been applied to the Lesmahagow coal, which, in his opinion, would have some what deteriorated the Lesmahagow coal gas.

The mean quantity of carburetted hydrogen gas in the Glasgow coal gas was 60.6 per cent.; the smallest quantity was 47.33, and the largest 79.77; the quantity of this gas in the gases from cannel coal was as follows:

Skaterigg, . 66.49
Lesmahagow, . 59.94
Monkland, . 48.77

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The goodness of these gases is in the order of naming them. would appear from this, that the smaller the proportion of carburetted hydrogen the better is the gas; the reason is that the olefiant gas increases as the carburretted hydrogen diminishes.

The average quantity of carbonic oxide in Glasgow gas was 12 per cent., the smallest quantity was 6.34 per cent., and the greatest quantity 15 per cent.: the quantity of this gas in the three gases from cannel coal was as follows:

Skaterigg, 7.07
Lesmahagow,. 12.00
Monkland, 11.76

The mean quantity of hydrogen gas in Glasgow gas was 12.44 per cent., the greatest quantity was 22.85 per cent., and the smallest quantity 2.21 per cent.: the quantity in the three gases from cannel coal was as follows:

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Lesmahagow, 11.46
Monkland, . 17.32

The common method of determining the light emitted by gas during its combustion, is to set fire to a jet of a given height, and issuing from an orifice of a given diameter, and to compare it with the light given out by a wax candle of six in the pound, usually denominated short sixes; an opake body is placed on a sheet of paper, horizontally between the two flames, and it is so placed that the two shadows formed by it are of equal intensity. The distance between this opake body and the flames is measured, and the light emitted by each is as the square of that distance; thus, if the distance between the gas flame and the opake body be two feet, while its distance from the flame of the candle is only one foot, then the light given out by the gas is four times as great as that of the candle.

The light given by the combustion of a jet of Glasgow gas, issuing from an orifice of 1-30th of an inch in diameter, and four inches in height, was as follows:

1. On the north side of the river=2.68 candles.
2. On the south side of the river=1.77

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This method of measuring the quantity of light appears, at first sight, very simple, but I found on trial that it was attended with so many sources of error, that I was afraid to depend upon it; fortunately there is another method of much easier execution, which I found much more satisfactory.

The quantity of light given out during the combustion of coal gas is very nearly proportional to its specific gravity; the heavier a gas is the slower does it issue from an orifice of a given diameter, when propelled by a given force. I measured the time which a cubic foot of each gas took to issue from an orifice of 1-30th of an inch, when propelled by a force such as to form a jet of flame, when lighted, of four inches in length, and I considered the goodness of the gas as proportional to this time: the result was as follows:

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Certainly, in a commercial point of view, the value of the gas (the price per cubic foot being the same in all,) is exactly proportional to the time that it takes to burn, because the consumption in a given time depends upon that time.

If, therefore, a thousand cubic feet of gas be charged 8s. on both sides of the river, it is clear that the consumers on the south side pay at the rate of 9s. 4d. per cubic foot, because they consume 7000 cubic feet in the same time that those on the north side consume 6000.

If Glasgow gas, Skaterigg gas, and Lesmahagow gas are each charged at 8s. per 1000 cubic feet, the price paid by the consumers

will be

1000 feet of Lesmahagow gas,

S. d.

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Summary of Experiments made with Screw Propeller and Rotary Engines fitted to Mr. Beale's trial boat, the "Pigmy Giant." By E. W. BAKER, late Engineer of the Prince of Wales.

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The "Pigmy Giant" was built of iron by Messrs. Ditchburn and Mare, of Black wall; she is 38 feet long, and of 8 feet 6 inches beam; 4 feet deep; her draught of water at midship 2 feet; midship section immersed 9 square feet; she drops at the stern when going well about 12 inches, and is built to draw one foot more at the stern than at the head. The boat was originally intended for government service, and is built from the lines of a man-of-war's pinnace. The engines and boilers used in the experiments, afterwards detailed, are the same as those described in No. 1056, of this journal. The furnace is urged by a fan. The calculations of the power of the engine contained in the table, a vacuum has been added equal to a column of mercury of 20 inches, and the speed of the vessel through the water is the mean of various experiments. The weight of the valve and lever, together with Salter's spring balance, (which will amply allow for friction and steam cooling in pipes, &c.,) are not taken into account. In the column showing the cubic feet of water pumped into the boiler, the contents of the plunger are taken as being equal to 11.6 cubic inches, and one-third is deducted from the gross amount for leakage, &c.

From the following table it will be perceived that this little vessel requires an extraordinary degree of pressure to acquire any thing like velocity, and although no correct account of her consumption of fuel has been kept, I can state from personal observation, that when exceeding a speed of 94, her consumption of best oven coke is nearly one cwt. per hour.

The propeller with which the experiments were made, was constructed by Mr. Joshua Taylor Beale, in imitation of Blaxland's, and is thus described by him in a paper originally intended for insertion in this journal; "Propeller is composed of four arms, and 4 segments of a screw, forming part of a four-threaded screw; its diameter 2 feet 14 inches, and 4 feet pitch; segments equal half radius surface of each ONE-FIFTH OF THREE QUARTERS of a disk the diameter of the propeller; the arms may be round, or square; the propelling surface two-ninths of midship section of boat; midship section of boat=9 square feet."

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Mr. J. B. Beale has discovered that one-fifth of three quarters, or in other words, three-twentieths, of a disk containing 510.7 square inches, will only contain 288, (this being the number of square inches

in two-ninths of 9 square feet,) instead of 306, the number usually assigned to it by other mathematicians. I must confess I do not understand this; perhaps Mr. Beale will explain.

Experiments with the "Pigmy Giant."

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The table, though not so perfect as could be wished, will enable the reader to form an opinion of this class of rotary engines, as it gives the rotary horse power requisite to propel 9 square feet of surface at a certain velocity. By comparing the results in this table with others obtained by the ordinary reciprocating engine, we shall have data to estimate which class of engine gives out the greatest effect.

It may not be out of place to add, that with a propeller constructed by Mr. Blaxland for trial in this boat, a speed of 10.5 was realized, which was the greatest ever attained by the Pigmy Giant. The same propeller divested of two of its blades, and containing less propelling surface than half of "one-fifth of three-quarters of a disk the diameter of the propeller," attained a speed of upwards of 10 miles per hour. A propeller of the same diameter, and with flat plates, when tried in this vessel, once reached a velocity of 6 miles per hour. Lond. Mechanics' Mag.

VOL. IX, 3RD SERIES-No. 2-FEBRUARY, 1845.

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