I do not know that we have, in any author, particular and separate directions concerning the ventilating of hospitals, crouded rooms, or dwelling-houses; or the making of proper drains for carrying off stagnant or putrid water. The want of such general information, on these subjects, has induced me to endeavour to recollect all I can of the many instructive conversations I have had upon these matters with that judicious and most accurate observer of Nature, Dr. Benjamin Franklin. I do this, in hopes that either the Doctor himself, or some other person well qualified for the task, may follow the example set in so masterly a manner, by Sir John Pringle, Bart. when speaking on the Preservation of the Health of Seamen.

It has long been observed, that if a number of persons are shut up in a small room, of which the internal air has little or no communication with the external, the respiration of those who are so confined renders, by degrees, the air of that room effete, and unfit for the support of life.

Dr. Franklin was, if I mistake not, the first who observed, that respiration communicated to the air a quality resembling the mephitic; such as that of the Grotto del Cane near Naples. The air impressed with this quality rises only to a certain height, beyond which it gradually loses it. The amendment begins in the upper part, and descends gradually, until the whole becomes capable of sustaining life. The Doctor confirmed this, by the following experiment. He breathed gently through a Tube into a deep glass mug, so as to impregnate all the air in the mug with this quality. He then put a lighted bougie into the mug; and upon touching the air therein, the flame was instantly extinguished. By frequently repeating this operation, the bougie gradually preserved its light longer in the mug, so as, in a short time, to retain it to the bottom of it; the air having totally lost the bad quality it had contracted from the breath blown into it.

At the same time that the lower part of the air is thus affected, an acrid noxious quality may be communicated to its upper part, in the room; occasioned by the volatile putrescent effluvia of the persons inclosed therein. “It is surprising, says Sir John Pringle, (in his Observations on the Diseases of the Army, 4th Edit. p. 109) in how few days the Air will be corrupted in close and crouded wards; and what makes it hard to remedy the evil is the difficulty of convincing, either the nurses or the sick themselves, of the necessity of opening the windows and doors, at any time, for a supply of fresh air.”

It may be inferred from the above account of mephitic air, that such air can be but little altered by a Ventilator in the cieling of a room; and Dr. Franklin justly concluded, that, in crouded rooms, and especially in bed-rooms, in dwelling-houses, a current of air should be kept up in the lower part of the houses [interlined: rooms], to carry off what is thus affected. He approved of the use of chimneys for this purpose, especially when the current is quickened by a fire. Even when there is not any fire in the chimney, a current of air is constantly kept up in it, by its ascending or descending in the flue, as the weight of the internal or external air preponderates. This creates a kind of tide in the flue, conducing much to the healthiness of the air in rooms: and hence we may see the injudiciousness of having chimney-boards which fit closely and thereby prevent a salutary circulation in the air. Hence also, in warm weather, we may account for liquors, or other things, kept in a chimney, being cooled; and more so, if means are used to create an evaporation around them.

Every person has an atmosphere of his own, heated by the warmth of his body, which can be dissipated only by a motion in the circumambiant air. Thus, in warm weather, wind cools the body, by carrying off the personal atmosphere; and by promoting, at the same time, a more free evaporation of the effluvia arising from the body. This creates a greater degree of coolness on the skin. The personal atmosphere can be but little affected by a ventilator in the cieling of a room, unless the admission of external air is so directed, as to act principally on the air surrounding those in the room. Dr. Franklin, when consulted on Ventilating the House of Commons, represented, that the personal atmosphere surrounding the Members might be carried off by making outlets in the perpendicular part of the seats, through which the air might be drawn off by Ventilators, so placed as to accomplish this without admitting any by the same channels. It will appear from what has been said, that windows placed high in the walls of churches, or in rooms intended for large assemblies, can contribute but little towards correcting the mephitic quality of the lower part of the air, or towards carrying off the personal atmospheres.

The experiments made for ventilating crouded rooms, by that most beneficent of men, the reverend Dr. Stephen Hales, bring evident proof how much the upper part of the air, in such places, is vitiated by the volatile putrescent effluvia arising from the persons present in such rooms. He at the same time shewed an easy and effectual way to carry off such vitiated air. His Ventilators were, however, attended with the inconveniency of occasioning smokey chimneys, by drawing off so much air, that there was not a suffiency left, to keep a current strong enough to carry the smoke up the chimney, unless a door or window was left open. The circulating Ventilators in windows were intended for refreshing the air in rooms, without affecting the current of air up the chimney: but they did not affect the mephitic air, nor the higher air, near the ceiling of lofty rooms, which is most vitiated with putrescent particles, and they were besides, often out of repair.

Instead of either of these, Dr. Franklin proposed, that openings should be made close to the ceilings of rooms, communicating with a flue, which should ascend in the wall, close to the flues of the chimneys; and, when it can be done conveniently, close to the flue of the kitchen-chimney; because the fire burning pretty constantly there, would keep the sides of the flue warmer than those of the other chimneys; whereby a quicker current of air would be kept up in the ventilating flue. Such a flue might be carried from the vaults or under-ground offices. This would render them dryer, without altering their temperature much, as to heat or cold. These ventilating flues would cause a constant discharge of the volatile putrescent effluvia, without interfering with the current of air up the chimneys; while the current towards the chimney would carry off the mephitic air below. These ventilating flues would be peculiarly beneficial in bed-rooms of which the ceilings are low.

Dr. Franklin mentioned an instance of a number of Germans, who, on their arrival in Pensilvania, were obliged to live in a large barn; there being at that time no other place of residence, fit for them. Several small windows were made on both sides of the barn, under the eaves. These windows were kept constantly open, even during a severe frost in the winter; and this, without any detriment to the health of the Germans. Prejudice, said he, has raised so great a dread against cold air, in England, that such openings would make every person shudder at the thought of being exposed to so great a degree of cold: and therefore I did not dare to recommend a practice, the good effects of which I had known. The Dormitory for the youths of Westminster School, is a similar instance: for the glass put in their high lofty windows is soon broken, but seldom repaired: yet without prejudice to the health of the youths.

There is a channel, by which much of the vitiated air escapes, and is but little attended to. Whoever looks at the cielings of rooms in old houses, will soon discover the traces of the rafters, by a difference in colour, in parts of the cieling: for wherever there is not a solid resistance to the passage of the air, much of it gets off, through the ceiling, and deposits in it part of its contents, which discolours the intervals between the joists. In the British Museum, there is a remarkable instance of the inconveniency of the want of this outlet. The ceiling of one of the rooms, in that house, is covered with a picture, or painted cloth. This room continues warm, with little fire; but the air soon affects the respiration of Valetudinarians; as was often remarked by that accurate observer, Dr. Gn. Knight, late principal Librarian.

An attentive observer will soon be convinced, that there is a current of warm air which ascends in the room from the chimney while a fire burns. Dr. Franklin shewed that this was the case, by the following experiment. He suspended, by a thread, a piece of pasteboard, cut in spiral form. The thread was fastened to the chimney-piece, so that the pasteboard, drawn out into a spiral form, came near to the edge of the chimney. The constant current of warm air, heated by the fire, gave a continued circular motion to the pasteboard. This warm air ascending to the ceiling, there spread, and kept a constant motion in the upper part of the air. The warm air thus ascending, coming into contact with the cool walls, and being thereby condensed, becomes heavier, and so falls along the sides of the walls. Also the glass in windows, being exposed to the temperature of the external air, in cold weather, becomes colder than any other part of the room; the warm air coming into contact with the glass is more condensed than the air in any other part of the room, and therefore more sensibly descends; as may be seen, by approaching a lighted bougie to a window. The flame is then carried downward by the air, or, if the flame is extinguished, the smoke will more clearly shew this truth, by descending along the window, till it meets with air of an equal temperature. This will be the case, however tight the window; and the more so, the brighter and stronger the fire is, and the colder the external air: the circulation of the air being thereby quickened. This accounts for the familiar caution of avoiding to sit in or near a window. This circulation of the air is yet more evidently proved by the following instance. When there is a bright strong fire, in a close room, open the door, and present immediately a lighted candle to the upper part of the door: the flame will bend outward; though warm air in the higher part rushes out. Lower the candle gradually, and the strength of the current outward will lessen by degrees, as the candle is lowered, till it comes to a space in which the flame shall rise upright: continue to lower the candle, gradually, and then the current of cold air, inward, will gradually increase, and more strongly bend the flame of the candle inward. This will be the case even in frosty and windy weather. May it not be inferred from this circumstance, of so strong a current of air outwards, in the upper part of the door, that an opening over, or in, the upper part of the door, in the ward of an hospital, might be of advantage; especially if there is no ventilating flue in the ceiling? By such means, a circulation of the air in the upper part of the ward could be constantly kept up; and thereby a vent would be given to the volatile putrescent particles. This vent might remain open at all times, without any prejudice to the patients.