men is merely volatilized, in the state of condensable tar. Little gas, and that of inferior illuminating power, is then produced. Why does coke burn without smoke? Because it is the distilled coal remaining in the retorts after the above process, and is consequently freed from all gases and vapours. Dr. Arnott observes, that "a pound of coke produces nearly as much heat as a pound of coal; but we must remember that a pound of coal gives only three-quarters of a pound of coke, although the latter is more bulky than the former.” Why are the gaseous products passed through quicklime and water? Because the sulphuretted hydrogen, and carbonic oxide and acid, may thus be absorbed; while the carburetted hydrogen gases are transmitted sufficiently pure for use into gasometers, whence the pipes issue for the supply of streets, houses, &c. Why is a gasometer so called? Because it enables the manufacturers of gas to mete, or measure, with accuracy, the quantity of gas expended, in proportion to the number of jets or burners made use of. The essential conditions of any apparatus for this purpose, are, that the pressure on the gas, while passing through the measurer, shall at all times be uniform: and that it shall register truly when that pressure is very small, and when the current of gas is very feeble. The gas is conveyed or laid on to the premises of the consumers, by pipes called mains, which, in London, in the year 1824, extended 900 miles. Other methods, have, however, been adopted for its conveyance; and, in 1827, there was at Manchester an itinerant gasometer, capable of holding more than 1000 cubic feet of gas; this being mounted upon wheels, and filled with gas from the gasometer at the works, was transported about the streets of Manchester, and delivered into the gas-holders of the Company's customers. Why is it important that the holes in the gas-burner be not too large ? Because, if this point be not attended to, the gas will be incompletely burnt. Increased length of flame makes imperfect combustion, and diminished intensity of light. Mr. Accum gives the following interesting statement of gas-burners. "An argand burner, which measures in the upper rim half an inch in diameter between the holes from which the gas issues, when furnished with five apertures, 1-25th part of an inch in diameter, consumes two cubic feet of gas in an hour, when the gas flame is 1 inch high. The illuminating power of this burner is equal to three tallow candles, eight in the pound. An argand burner, three-fourths of an inch in diameter, as above, and perforated with holes 1-30th of an inch in diameter (probably fifteen in number) consumes three cubic feet of gas in an hour, when the flame is 24 inches high; giving the light of four candles, eight to the pound. And an argand burner, seven-eighths of an inch diameter, as above, perforated with eighteen holes, 1-32nd of an inch diameter, consumes, when the flame is three inches high, four cubic feet of gas per hour, producing the light of six tallow candles, eight to the pound. The height oft he glass chimney should never be less than five inches. Why is cannel coal best adapted for distillation ? Because it contains most bitumen, and least sulphur. A pound of good cannel coal, properly treated in a small apparatus, will yield five cubic feet of gas; equivalent in illuminating power to a mould candle, six in the pound. On a great scale, however, 3 cubic feet of good gas are all that should be expected from one pound of coal. A gas jet, which consumes half a cubic foot per hour, affords a steady light equal to that of the above candle. Why does carburetted hydrogen give out, during its combustion, much more light than the subcarburetted? Because of the larger quantity of carbon disengaged by the former; but if the mixture with oxygen be in such proportions as at once to burn the whole of the charcoal in its gaseous combinations, without previous deposition, the light becomes blue, and is greatly reduced in intensity. Why is the flame of a candle of various colours? Because of the different stages of combustion in it. Thus, at the bottom part, where the inflammable gases are given off in the smallest quantity, and where they are most intimately mixed with the air, the combustion is at once complete, and the light is blue and faint; the centre part, where the particles of charcoal, owing to a less admixture of oxygen, are thrown off in a solid state, and become incandescent before they are finally burnt, is white and highly brilliant; and the upper, where the charcoal is in still greater quantity, and much of it finally escapes combustion, is red and dull, as is seen when a candle requires snuffing. Dr. Ure, a few years since, made a set of experiments on the relative intensities of light, and duration of different candles, the result of which is contained in the following table : Why do those flames, whose products are only gaseous matter, give very little light? Because the quantity of light which flame emits is dependent upon the incandescence of minute particles of solid matter, which are thrown off during combus tion. The light of a stream of ignited hydrogen is scarcely visible in the day-light; but if a small coil of platinum wire be suspended in it, or some solid body, in very fine powder, such as the oxide of zinc, be projected through it, it becomes very luminous. OIL GAS. Why is oil gas cheaper than coal gas s? Because purified coal gas seldom contains more than 40 per cent. in volume of olefiant gas, while oil gas generally affords about 75 per cent.: hence its superiority for burning, and the relatively small quantity consumed. Thus oil, by being allowed to trickle into a red-hot retort, half filled with coke or pieces of brick, to increase the heated surface, is decomposed, and yields a large quantity of gas, which is much richer in carburetted hydrogen than coal gas, and therefore much better fitted for the purposes of illumination. It contains no mixture of sulphuretted hydrogen, and requires no other purification than passing through a refrigerator; and as less of it is required for any given quantity of light, the atmosphere of a room is less heated and contaminated by its combustion. It is, however, considerably more expensive than the gas from coal; although the first outlay of capital for a manufactory upon a large scale is less, on account of the smaller size of the necessary pipes and apparatus. The commonest whale oil, or even pilchard-dregs, quite unfit for burning in the usual way, afford abundance of excellent gas. A gallon of whale oil affords about 90 cubical feet of gas, of an average specific gravity of 0.900; and an argand burner, equal to seven candles, consumes a cubical foot and a half per hour. Its economy may be judged from the following table : Mr. Brande adds, that a pint of the best sperm oil, weighing about 13 ounces, burns, in a well trimmed argand, about ten hours. And by a series of experiments, conducted with every requisite caution, he found, that to produce the light of ten wax candles for one hour, there were required 2600 cubical inches of pure carburetted hydrogen, or olefiant gas. 4875 13120. gas. ..oil Why is oil used by the Portable Gas Company? Because they are enabled to compress the gaseous matter obtained from oil to about one-thirtieth of its volume, or into a certain new liquid compound, colourless or opalescent, yellow by transmitted, green by reflected light; and combustible, burning with a dense flame. Hence its portability. When the bottle containing it is opened, evaporation takes place from the surface of the liquid; but this vapour soon ceases, and the remainder is comparatively fixed. Why is gas from wood but ill adapted for illumination ? Because it is so deficient in the compounds of carbon and hydrogen. In manufactories, however, of charcoal in iron retorts, for the making of gunpowder, the gas which is given off is led by a pipe under the cylinders, and is economically employed in maintaining their heat. ROSIN GAS. Why is rosin gas even more advantageous than oil gas? Because rosin is of lower price, and less liable to fluctuations of value, than oil: indeed, the cost of the gas is stated at one-fourth that of oil; and the illuminating power of rosin gas, when compared with that from coal, is as two and a half to one, while it is of greater purity than that from coal or oil. For the origin of this improvement we are indebted to Mr. J. F. Daniell, the distinguished meteorologist: his mode of treating the rosin is, to dissolve by gentle |