Chimney (Lat. caminvs, Gr. a furnace), the flue for producing a draught and conveying off the smoke of a fire. Simple as these contrivances are, chimneys do not appear to have been known in ancient times. According to Tomlinson, they were probably in use in England before those of Padua, the earliest record of which carries them back to some period previous to 1368, when Carraro, lord of Padua, introduced them into Rome. But the use of the curfew bell in preceding centuries indicates their absence, when the practice prevailed of thus summoning the people to cover over the fires that burned in pits in the centre of the floor, under an opening in the roof. In Venice they appear to have been common in the 14th century, a number being thrown down, it is recorded, by an earthquake on Jan. 25, 1347. Leland thus speaks of Bolton castle, which he says "was finiched or kynge Richard the 2 dyed:1' "One thynge I muche notyd in the hawle of Bolton, how chimeneys were conveyed by tunnells made on the syds of the walls betwyxt the lights in the hawle, and by this means, and by no covers, is the smoke of the harthe in the hawle wonder strangely conveyed." But for centuries afterward they appear to have been known only as luxuries in the houses of the great; and in the time of Queen Elizabeth visitors were occasionally sent to houses thus provided, that they might have the enjoyment of this convenience.
Beckmann, in his " History of Inventions," has gathered from ancient sources many curious allusions to what in our translations are called chimneys; but these appear after all to have been nothing better than holes in the roof, through which the smoke found its way out, as from the wigwams of the American Indians. Neither Vitruvius nor Julius Pollux, an ancient lexicographer, who gives the names of all parts of a house in Greek, nor Grapaldi, who does the same in Latin, makes mention of chimneys. Among the most ancient ruins no traces of them are found, nor have any been discovered in Herculaneum, though charcoal has been met with in some of the apartments. The mode of warming rooms appears to have been to place upon the floor a portable pan or furnace containing live coals. Hence the propriety of the observation of the poet Sosipater, that one qualification of a perfect cook was the art of determining which way the wind blows; and also of the advice of Vitruvius, that there should be only plain cornices in rooms where there are to be fires and lights, as more elaborate ornaments would soon be filled with soot.
Anacharsis, the Scythian, speaks of the Greeks keeping the smoke without, and bringing only fire into their houses; and Heliogabalus is said by Lampridius to have burned in the stoves spices and costly perfumes instead of wood. The Persians, who still retain some of the most ancient customs, are described by Pietro della Velle as making their fires in a round or square hole in the earth floor of their apartments, in which is an iron vessel containing the fuel. Over it is placed a low table, covered with a thick quilted cloth, reaching to the floor. The heat is described as being exceedingly agreeable, and not causing uneasiness to the head, though no provision is made for conveying away the gaseous products of combustion. A pipe for blowing the fire with the mouth is made to project up from the floor. - To such expedients were the most refined nations of antiquity probably reduced in their ignorance of the simple chimney flue; a fact which would seem quite irreconcilable with the progress they had made in many of the arts dependent more or less upon the use of fires, were it not that these were less essential to them than to the inhabitants of more northern latitudes.
The tendency of heated air to ascend must have been almost as familiar to them as that of water to flow down inclined planes; and to us it would seem to require not much more ingenuity to devise pipes for conveying the former away, than to contrive aqueducts which to this day are regarded as extraordinary works of art. It was the every-day need of supplies of pure water, and not of artificial warmth, which alone made the difference. This tendency of warm air to form ascending currents comes from its greater proportional lightness as it is expanded by heat and made to occupy a greater space. Deep mines in cold countries well exemplify the working of this principle. In the winter season the deep shafts are perfect chimneys of ventilation. The air enters the mines through the lowest openings into them, and mixing with the smoke of the candles and of the gunpowder blasts, acquires from these, and from the warmer underground temperature, a greater heat than that of the air above. Expanding in bulk, it floats upward, establishing an ascending current, which is renewed by succeeding portions of air, and which rapidly sweeps off the gaseous impurities of the mine.
But as the weather becomes warm, and the air within and without attains the same temperature, no such current is formed, and the smoke, settling in a cloud below, slowly finds its way out by those passages through which at other times the fresh air is wont to flow in. Artificial means of ventilation then become necessary. Fires are built in the mine or at the mouth of the shaft, and the foul air is also forced out by blowing machines. The ascensional power of a column of heated air is the difference between its weight and that of an outside column of the same height. It is hence increased by adding to the height of the chimney, as well as by increasing the temperature. But the chimney may be so high, especially when exposed in cold situations, that the heat taken up below may be dispersed before the air reaches the top. In this case increased height adds nothing to the draught, but diminishes it. Short chimneys may be made more effectual by increasing the temperature, and in locomotives this is done by the introduction of a jet of hot steam. Calculations have been made to estimate the ascending force of air in chimneys at any given increase of temperature over the external air; but these are affected by many sources of error, which render the results only approximate.
The flow of air over rough surfaces is retarded by increased friction, and in small flues it experiences this resistance more than in large ones of the same construction, in the inverse proportion of the diameters of the flues. In order to apply these calculations, it is necessary to know the mean temperature of the column of air in a chimney, and this cannot be determined with accuracy. It may be approximated by finding the degree of heat a little above the lower entrance into the flue, and that at the top, and taking half of their sum. Mont-golfier, the inventor of balloons, first gave attention to this subject, and proposed the following method of determining the force of the draught, or the velocity of the current, which is still considered as simple and accurate as the case admits of. It is the same velocity which a falling body would acquire in passing the distance equal to the difference in height between two equal columns of air at the different temperatures. As the velocity of a heavy foiling body is ascertained at any period of its descent by multiplying the square root of the number of feet it has fallen by 8, which gives its rate per second of time, we have the data for applying to the calculations for determining the velocity of the current.
Suppose the height of the chimney to be 70 ft., and the difference of temperature of the two columns to be 30°, we have the expansion of the heated column= 70 x .0661 (this decimal representing one sixth of the expansion due to a difference of 180° of temperature). The difference in the height of the two columns is then 4.627 ft., and the square root of this (2.15), being multiplied by 8, gives 17.2 ft. per second as the velocity of the draught. For the further consideration of chimneys especially intended to feed fires with a draught of air, see Furnace. - Smoky chimneys have a variety of causes, such as imperfections in the flue, too contracted dimensions, too rough an inner surface, openings which admit cold air and chill it, and, the most common of all, too large an opening at the fireplace or throat. Count Rumford paid much attention to the cure of smoking chimneys, He generally found the cause to be too large a throat, and his usual remedy was to diminish it by building a bench of brick in the back of the fireplace, reaching up to the throat, and to lower the fireplace somewhat.
Sometimes the aperture at the top is too large, particularly if it is below the level of some neighboring house, hill, or high trees, from which the wind may be reflected down into the chimney, or over which it may fall, and thus beat down the smoke. An inadequate admission of air into the room in which is the fireplace will cause a chimney to smoke, a circulating current being thus as effectually prevented as if the flue itself were in great part obstructed. The opening of a door or window often shows the cause of this trouble by at once removing it. When two chimney flues come down into one room, or into two rooms which connect by an open passage, the burning of a fire in one flue may establish an upward current, which is supplied with air drawn down the other. Any attempts to make the second chimney draw could only succeed by closing the connection between them, or supplying the first with the air it requires from some other source. When a chimney smokes in consequence of the wind beating down, the height may be increased, or the diameter at the top contracted; but the most efficient remedy is usually found by adjusting a bent tube to the top of the chimney, and keeping its mouth turned in the direction of the current of air by means of a vane.
The effect of the latter change is to admit a smaller quantity of air, and this is dispersed through the large body in the flue without being felt at the base. The worst chimneys usually draw well when a stove is substituted for the fireplace, and the pipe is led into the chimney. This causes an increased current in the smaller channel, being equivalent to contracting the throat of the chimney when the fireplace is used. - Tall chimneys are built to convey away the noxious fumes from chemical and manufacturing establishments, and relieve the neighborhood of the nuisance these would otherwise occasion. They are built up from a solid base, with side flues leading into the central cavity. The size of this cavity should, as in the chimneys of dwelling houses, be of rather larger area than the sum of that of the flues which lead into it. In large stacks it varies from 3 to 6 ft. in diameter. They are constructed with a brick lining, so laid as to leave an air space between it and the outer wall, the effect of this being to check the rapid dispersion of the warmth of the vapors. A chimney of this kind has been erected at Manchester, England, 415 ft. high, 25 ft. square at the base, and 9 ft. at the top. It required to build it 4,000,000 bricks.
At the Thomas iron works, on the Lehigh river in Pennsylvania, are cylindrical chimneys of a thin boiler-plate iron casing, lined with fire brick; the casing being 7 ft. in diameter, and the fire brick a foot long, made and bevelled to fit the circle, the internal diameter is 5 ft. These chimneys, for their capacity, are light, substantial, and elegant; but they are not built with reference to retaining the heat of the vapors, which is here no object.