AIR, in Medicine, &c. makes one of the six non-naturals.—From observations on bleeding in rheumatism, and after taking cold, it is evident, the air can enter with all its qualities, and vitiate the whole texture of the blood, and other juices.—From the palsies, vertigoes, and other nervous affections caused by damps, mimes, &c. it is evident, that air thus qualified can relax and obstruct the whole nervous system. And from the colics, fluxes, coughs, and consumptions produced by damp, moist, and nitrous air, it is evident it can corrupt and spoil the noble organs, &c.
Circulation of AIR in Rooms. To render the circulation of air sensible, let the air of a room be heated by a strong fire, whilst the air of a contiguous room is cold; then let the door between these two rooms be opened, in which case the hot air of one room being lighter, will pass through the upper part of the opening of the door into the cold room; and, on the contrary, the cold
Air cold air of the other room being heavier, will pass into the former room through the lower part of the opening; accordingly, it will be found, that applying a lighted candle at the top, in the middle, and at the lower part of the opening between the two rooms, a strong current of air will appear to pass from the hot into the cold room near the top; a contrary current of air will appear to pass from the latter into the former room near the lower part of the said opening; whilst in the middle there is little or no motion at all, as may be clearly perceived by the direction of the flame of the candle.
It is for the same reason that when the fire is lighted in a chimney, a strong current of air is occasioned to enter the room, which may be felt by applying the hand near the key-hole, or other such small openings, if the doors and windows are shut; for the air over the fire being heated, becomes lighter, and ascends into the chimney, consequently other colder air must supply its place, which forces its way through all the small openings it can find. Were a room with a fire in it to be perfectly closed, excepting the chimney, the air in it would soon become unwholesome for respiration, and the fire would be soon extinguished, besides other inconveniences. Hence it appears, that those persons mistake who expect to keep the air of a room sweet and wholesome, especially for convalescents, by accurately stopping all the smallest openings that admit fresh air. When the current of air that enters into a room is on some side of it where it falls immediately upon the persons who sit in the room, then it may be offensive, especially to delicate constitutions. In that case, such opening should be closed: but at the same time another opening should be made for admitting fresh air, in another more convenient part; for a circulation of air, especially in rooms where a fire is kept, is not only salutary and useful, but is absolutely necessary.
In an ingenious publication, intitled, A Practical Treatise on Chimneys, there are the following remarks relating to the properest method of admitting air into a room, and of expelling the contaminated air. The author, directing to make a vent-hole near the top of the room, in order to expel the heated and contaminated air, "this," says he "might be done by means of a small tube opening into the room, either in or near the ceiling; which might either be carried to the top of the building, or be made to communicate with the external air by a small perforation through the wall at the roof of the room; by means of either of which, a proper circulation would be established, and the foul air be carried off.
No 9.
Air "For the fire would no sooner have warmed any particles of air within the room, than these would be greatly expanded, and rise immediately upwards, so as to fill the higher parts of the room with rarefied air; and as other particles would be successively heated and rarefied in their turn, by their expansive force they would press upon the sides of the apartment in every place, so as to force the lightest particles through the opening left for that purpose in the top of the room; by which means the foulest air would be gradually drawn off, without descending again into the lower regions to the annoyance of the company."
But in order to admit fresh air into the room, "Let," says he, "another opening be made in the ceiling of the room, having a communication with a small pipe that should lead from thence either to the outside of the wall, or to any other part of the building that might be judged more convenient, where it should be bent, and conducted downwards, till it reached the ground; where it should be left open, to communicate with the external air.—In this situation the cool external air would be forced in at the lower opening of the tube, and made to ascend into the apartment in proportion to the quantity that escaped towards the higher regions by means of the ventilator. And as that weighty air would no sooner enter the room, than it would tend towards the floor by its own natural gravity, it would gradually mix with the heated air in its descent—become, in some measure, warmed by that means, and equally dispersed through the room, so as slowly and imperceptibly to reach the candles and the company in the room, and supply them with a sufficient quantity of fresh and wholesome air, without the inconveniences to which the company are subjected by the usual way of admitting fresh air (A). For if it enters near the floor of the apartment, it is hurried along in a rapid undivided stream towards the fire-place, and striking upon the legs and inferior parts of the body, affects them with a strong sensation of cold. To overcome the effects of this, large fires must be kept; by which other parts of the body are warmed to an extraordinary degree, which is productive of most of those disorders that are pernicious to the young, and often prove fatal to the old, during the winter-season, in these cold regions.
"Thus might our apartments be kept constantly, and moderately, and equally warm, at a moderate expense, without endangering our health on the one hand, by respiring a confined, stagnant, and putrid air, or, on the other hand, by subjecting ourselves to such danger of catching colds, consumptions, and rheumatic complaints, by being exposed to such exceedingly unequal
(A) Such readers as have been little accustomed to speculations of this sort, will be at a loss to comprehend in what manner two holes, both of them in the roof of the room, and communicating with the air, without any valve, or other contrivance, for opening or closing of themselves, should yet answer the two very opposite purposes; one, of constantly bringing cool air into the room without emitting any warm air—and the other, of as constantly emitting warm and admitting no cool air. They will please to advert, that the one of these tubes communicates with the atmosphere at the bottom of the house, and the other towards the top: the opening of the one is beneath the level of the room, that of the other above it. Now, as the air is more dense at the surface of the ground than at any height above it, the warm rarefying air will naturally issue at that opening where it meets with least resistance, which must invariably be through that which opens to the external air at the greatest height; and as the cool air will naturally be pressed into the room by that opening where the air is most weighty, this must invariably be by that which is nearest the surface of the earth.
Air
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Air-gun.
equal degrees of heat and cold, as are unavoidable where our apartments are so open as to admit a ready passage to the external air during the winter-season.
"The reader will easily perceive, that all that has been here said has a reference only to those apartments in cold climates, and rigorous weather, where fire to warm them becomes necessary. In warmer regions, or during the summer-season, there can be no objection to the wheel-ventilator in the window.—It is a simple contrivance, and a safe and effectual mean of preserving the air in our apartments sweet and wholesome at that season."
It is a vulgar error among many people, to believe that fire purifies the contaminated air, by destroying the noxious particles mixed with it; and for this reason they think, that the fire kept in a room where the air is tainted, purifies the room, by rendering the air in it again fit for respiration. Indeed, a fire kept in a room or apartment where the air is tainted, as is the case with hospitals, goals, and the like, does certainly purify the apartment, and the practice is very useful; but this effect is only because the fire promotes the circulation of the air, and dries the dampness of rooms, furniture, &c.: so that it is not the infected air that is purified, but is new, fresh, and wholesome air, that by the action of the fire has taken the place of the infected air; which infected air, being rarefied by the heat, has been expelled from the apartment. Fire and combustion in general is so far from purifying contaminated air, that it actually contaminates a prodigious quantity of it in a short time; so that not only a common fire, but even a lighted candle, when kept in a well-closed room, wherein the external air has not a free access, instead of purifying, renders the air of that room noxious.
Instrument for ascertaining the Purity or Wholesomeness of respirable AIR. See EUDIOMETER.