Front Page Titles (by Subject) CCCLXIX: ON VENTILATION - The Works of Benjamin Franklin, Vol. V Letters and Misc. Writings 1768-1772
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CCCLXIX: ON VENTILATION - Benjamin Franklin, The Works of Benjamin Franklin, Vol. V Letters and Misc. Writings 1768-1772 
The Works of Benjamin Franklin, including the Private as well as the Official and Scientific Correspondence, together with the Unmutilated and Correct Version of the Autobiography, compiled and edited by John Bigelow (New York: G.P. Putnam’s Sons, 1904). The Federal Edition in 12 volumes. Vol. V (Letters and Misc. Writings 1768-1772).
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I do not know that we have in any author particular and separate directions concerning the ventilating of hospitals, crowded 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, Baronet, 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 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 enclosed therein. “It is surprising,” says Sir John Pringle, in his Observations on the Diseases of the Army, fourth edition, p. 109, “in how few days the air will be corrupted in close and crowded wards; and what makes it hard to remedy the evil, is the difficulty of convincing either 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 ceiling of a room; and Dr. Franklin justly concluded, that in crowded rooms, and especially in bedrooms in dwelling-houses, a current of air should be kept up in the lower part of the 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 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 motion in the circumambient air. Thus in warm weather, wind cools the body, by carrying off the personal atmosphere, and promoting at the same time a more free evaporation of the effluvia arising from the body. This creates a great degree of coolness on the skin. The personal atmosphere can be but little affected by a ventilator in the ceiling 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 parts 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 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 crowded 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 showed an easy and effectual way to carry off such vitiated air. His ventilators were, however, attended with the inconveniency of occasioning smoky chimneys, by drawing off so much air, that there was not a sufficiency 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, where 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 that 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 drier, 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 bedrooms of which the ceilings are low.
Dr. Franklin mentioned an instance of a number of Germans, who on their arrival in Pennsylvania 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 ceilings of rooms in old houses, will soon discover the traces of the rafters, by a difference in color, in parts of the ceiling, 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 discolors 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. The room continues warm with little fire; but the air soon affects the respiration of valetudinarians, as was often remarked by that accurate observer, Dr. G. Knight, late principal librarian.
Vaulted rooms may be considered in this light; because the materials of which the arch is built must generally be solid. If the arch is built of stones, and these are exposed to the air, as they cannot so soon as wood or brick become of the temperature of the air, as to heat and cold, the vault must become wet on every change of the air, from cold to warm, as every one may observe in the walls and furniture of rooms in which fire is not kept. The vault may thus become a frequent source of moisture, which, mixing with the air, may gradually descend into the room, and become very prejudicial to the health of persons of weak constitutions, who may inhabit such rooms.
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 showed that this was the case by the following experiment: He suspended, by a thread, a piece of pasteboard cut in a spiral form. The thread was fastened to the chimney-piece, so that the pasteboard, drawn out in 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; therefore the internal air more sensibly descends, as may be seen by approaching a lighted bougie to a window. The flame is then carried downwards by the air; or, if the flame is extinguished, the smoke will more clearly show this truth, by descending along the window till it meets the 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-way, 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-way, that an opening over or in the upper part of the door in the ward of a 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 be left open at all times, without any prejudice to the patients.
What is said on this subject by Dr. John Armstrong, a gentleman no less remarkable for his benevolence than for his judgment and fine taste, may be properly mentioned here. “A constant circulation of fresh air is so necessary, so important in fevers and in all feverish disorders, that it ought to be particularly considered in the construction of houses. It would be well, if in all the apartments of every house, but especially in bed-chambers, the upper sashes of every window were contrived to let down; for by this means the admission of fresh air would at all times be perfectly safe, except during a raw, damp, foggy night; as the body, even when under such a sweat as could not without danger be interrupted, may receive all the refreshing, restorative, and invigorating influence of the air, without being exposed to a stream of it; meantime, where this is wanting, the best method to supply it is by drawing the bed-curtains close, now and then, for a few minutes at a time, while a free passage is made to the foul air, by opening the doors and windows.”—Medical Essays, p. 22.
The noxious vapors that fill a sick-room are not only offensive but dangerous to those who continue in it for any time. If dangerous to people then in health, how detrimental must they be to one oppressed and struggling under an enfeebling disease! It is a common thing in a campaign to distribute the sick soldiers, ill of malignant fevers, in open barns, where the putrid volatile poison is in a short time dissipated.
There is, in a volume of the Mémoires et Observations recueillies par la Société Economique de Berne, a letter concerning the health of the inhabitants of the Pays de Vaud; part of which I beg to present here, as bearing a near analogy to this subject. The letter is written by a most accurate and judicious clergyman. “One fact,” says he, “deserves to be noticed. Taking one year with another, a greater proportional number always die in towns than in villages. But whence comes it that, when epidemic diseases prevail, the mortality takes quite a different road; that is, it is much more considerable in villages than in towns? I have taken great pains to find out the cause of this phenomenon, and am apt to impute the difference to the difference of habitations. The poor in cities and great towns dwell in houses not originally intended for them; but which, being so old and past repairing, as to be no longer tenantable by persons at their ease, fall to the lot of the lower class of people. In these houses the rooms are spacious, cold as ice, where the air plays freely around, with doors and windows that do not half shut. The inhabitants of these shattered houses are pitied; and yet the very circumstance of their being out of repair, is what contributes to the health of those who live in them, and facilitates their cure when diseases reign.”
The more I see of hospitals, the more I am convinced of the great want of instructions on duly ventilating them. It is surprising to see what little attention has been paid in some hospitals about London to this article, which have been built since the importance of ventilation has been well known. In all of them there is too great a distance between the windows and the ceilings, where the volatile putrescent particles may remain till they become very acrid. With pleasure I here do justice to the judgment and precaution of Messrs. Adam, in the manner of ventilating the great room built by them for the meeting of the Society for the Encouragement of Arts, &c., by leaving spaces between the panes of glass in the sky-lights, the panes overlaying each other. These spaces being concealed from the eye, do not alarm those fearful of cold air, and keep the room constantly sweet.
The hospitals most judiciously built in this respect, which I have seen, are those in Philadelphia and in Lyons. In the hospital in Philadelphia the wards are two stories high, with two rows of windows in each, the upper row being kept generally open: and the windows in the hospital at Lyons are very lofty, so that the upper sashes may be for the most part kept open. Both hospitals are by this means perfectly sweet; so sweet that a military gentleman, who went with me into the hospital at Lyons, and was unaccustomed to sick-rooms, declared that the air in the ward was not disagreeable to him, though it contained a considerable number of sick. Indeed they were kept very clean. I am sorry to say this is not the case in any one of our hospitals.
The naval hospital at Gibraltar, is a square, which in a hot climate is itself a great imperfection, as the air within the square must, in summer especially, be greatly heated; and, as if they had studied to keep the cool air out of the wards, the windows open into the square only; whereas, if the west side had been left open, the wards might have received the cool breezes from the Bay. The sick are lodged in long galleries not sufficiently divided to have the patients in separate wards, and no openings to carry off the putrid air lodged among the rafters which support the roof.
On my arrival in the island of Minorca, as surgeon to the royal artillery there, I was surprised at the neglect of my predecessors in that office in regard to ventilating the hospital. There were no openings in the wards in which the sick lay but the windows and doors, which were necessarily shut every night, to prevent the irregularities soldiers might be guilty of. Where chimneys had been they were built up to prevent the expense of fires; and thus, during the night, the sick lay in absolutely confined air. The consequence was that when the nurse opened the wards in the morning she was obliged to withdraw instantly, for the highly infected air often brought on vomiting. In this case I applied to our most worthy and ingenious chief engineer, the late Colonel Mackellar for leave to use such means as might create a circulation of air in all the wards. In this he readily concurred, and ordered the necessary alterations.
In each ward in which the flue of the chimney remained, an opening of about four or five inches square was made through the wall into the flue, as near the ceiling as possible. Round holes of about three inches diameter were cut low in each door, covered with a sliding flap to shut the holes occasionally. In some of the wards there never had been chimneys. In these, holes were cut through the wall close to the ceiling, which opened into a common passage; and when two such wards were contiguous, a hole was cut through the dividing wall as well as in the door of each ward. One of the wards in which there had not been a chimney, and which was arched with stones, was constantly so damp that no use was made of it. The walls and arch were covered with green moss. They were afterwards scraped, to clear them of the moss which retained moisture, and then covered with lime. This room became so dry, that though locked up for three months, during which I was confined with the gout, books and papers which had remained in it were at the end of that time perfectly dry. The generally agreeable effects of this opening can scarcely be conceived; the wards, and indeed the whole hospital, being rendered perfectly sweet, greatly to the benefit of the sick, as well as to the pleasure of the attendants.
The barracks in the square of the Castle St. Philip, in which are lodged the detachment of the regiment of artillery doing duty there, are dry, except that, being built of stone, they collect moisture on every sudden change of the air from cold to warm. Each barrack opens into the square, and is divided into three apartments. The part next the door has the whole height, and in it their arms and necessaries are kept. The inner part, being about one half, is divided into two floors. In the lower room they cook, each barrack having a mess or family in it, some of whom sleep in it. The fire, and the free access between it and the door, keep up a due circulation here. In the upper room most of the men sleep under a stone arch, the room being little more than six feet high in the centre, and therefore much lower in the sides. Under that arch from four to six or eight persons sleep, especially when there are children. This room is very stifling, there being little circulation of air in it, more especially in calm, warm weather, such as the nights generally are there in summer. In order to create a circulation of air in this upper room, openings were made into the flues of the chimneys of the lower room, as near the centre of the arch as possible, the chimneys being in the corner of the rooms below. In general these openings drew very well, and gave great relief, especially to those who had weak or diseased lungs. The proper remedy here would have been to have had small flues made near the flues of the chimneys below, could it have been done. This measure is too much neglected in all barracks.
Whoever may on any future occasion have the direction of military hospitals, is already furnished with such judicious directions by my learned friends Sir John Pringle, Baronet, and Dr. Donald Munro, that, were I to say any thing on that subject, I could only copy whole pages from them. Sir John Pringle’s speech on giving the gold medal of the Royal Society to Captain Cook, in which he took occasion to point out the means of preserving the health of seamen, is equally deserving of commendation.
The healthiness of buildings does not perhaps depend more on the due ventilation of the rooms than it does on the dryness of the situation and of the foundation. Sir John Pringle, in the first part of his Observations on the Diseases of the Army, has given several instances of this truth. But as every man who regards his own life and health, or the lives and health of others, should be well acquainted with that work, I shall refer to the original. I have often lamented that the first part of that book, describing the natural consequences of the situation of places and their effects on health, has not been published separately, because it might thereby become of more general use to every man who leads country life, or resorts thither frequently to enjoy quiet; for being part of a book professedly treating of diseases, few think of consulting it, except whose business it is to cure diseases.
However inviting the situation may be, and whatever may be the quality of the ground on which houses are built, generally drains should be made all around the house deeper than the foundation of the building, to carry off the superfluous moisture, even the moisture that may be lodged under the ground; for it is essentially necessary that the lower part of the house be kept continually dry.
The advantages of drains or sewers are remarkably felt in London, which, before the fire of London, was frequently afflicted with contagious malignant fevers. Before that period all the waste water and filth remained above ground, and the people, as Erasmus complained, were very inattentive to keeping their houses clean. The wooden houses projected so much over the then very narrow streets that the air became almost stagnant, and must have been loaded with putrid effluvia, there being very little circulation or current in the air, thus confined, to carry off these effluvia.
Before the city was rebuilt, that ingenious architect, Sir Christopher Wren, planned and built the common sewers, as they continue to this day; and they are a lasting monument of his judgment and attention to the health and welfare of its inhabitants. These, together with the removal of signs and signposts, new paving and cleansing the streets, have been attended with such happy effects that London and Westminster are now ranked among the most healthy spots in the island for grown persons whose lungs can bear the cloud of smoke which generally hovers over them, and thus the apparent great calamity of a fire became a singular blessing to the city of London.
The quantity or water brought into the city by the New River and other water-works, which runs daily to waste, helps to cleanse and keep the common sewers sweet, and thereby contributes much to the healthiness of the city. Though foreign to the subject, it may be observed that till the Restoration there were few gardens about London for supplying kitchen herbs. These became more numerous after that period, and still more so after the Revolution, a number of Dutch gardeners coming to England at that time. The quantity of vegetables supplied by these gardens contribute greatly to the healthiness of the citizens.
Rome would not perhaps have become mistress of so extraordinary an empire, situated as that city is near marshy grounds, had not the common sewers, which still attract the admiration of all travellers, been so early and judiciously built by Tarquinius Priscus, who may for that reason be called a second founder of Rome. The ancient Romans were particularly attentive to the draining and cultivating of these marshes, and they soon became the granary of ancient Rome; but being neglected during the invasions of the barbarous nations, they are now the reproach and just chastisement of the supine indolence and inactivity of the modern Romans.
Gravel, which is generally reckoned a dry and healthy foundation to build upon, is found by experience not to deserve that character at all times, unless deep drains are made to carry off the water of heavy rains long continued; for by such rains the gravel may be so charged with water, especially in flat grounds, that the lower parts of the houses erected on such soils may prove damp. In all the flat grounds along the Thames the cellars are often filled with water after heavy rains; and if the water continues there stagnant till the animal or vegetable substances mixed with it begin to putrefy, aches, agues, and putrid fevers are the natural consequences. Though Kensington Palace stands high and on a declivity yet when King George the Second continued there till late in October, the lower parts of the house became damp, occasioned by the want of drains, and the servants became aguish. Stones which absorb and retain water, as the Cantoon stone in Minorca does, are in this respect similar to gravel. There was a remarkable instance of this in a magazine cut out of a solid rock of Cantoon stone in Georgetown, in Minorca. The magazine was covered with a well-limed arch and roof. Yet when the winter rains began to fall in November, the magazine was filled with water, as high as it was cut out of the rock. When drains were made to carry off the water, the magazine then became and continued to be sufficiently dry.
Might not low grounds on the banks of rivers, similar to those in Flanders, and so justly and judiciously complained of by Sir John Pringle, be rendered more healthy by drains dug as deep as low-water mark in the adjacent rivers? Sluices might be made in the banks of the river, to prevent the tides or floods from entering into the drains. It would be advisable to cover the drains, to prevent the noxious vapors arising from putrid vegetable or animal substances, which generally rot in open ditches. The earth thrown out of the drains might serve to cover them, when the channels for carrying off the water are properly constructed. By these means no surface would be lost for the growth of vegetables.
Willows, alders, and such trees as delight in a moist or wet soil may be planted on the banks of ditches, if any such are permitted to remain open, that their leaves may correct the putrid vapors arising from the stagnant water in the ditches. I fear, however, that in the autumn, when the effects of putrid vapors are most severely felt, the leaves of these trees, being then hardened by age, may in a great measure lose the power of correcting the putrid vapors. The late summer shoots may afford aid till the equinoxial rains clear the ditches of all filth. That trees have not the power of proving an effectual remedy against these putrid exhalations, the frequency of agues in the Low Countries, in every season, is a sufficient proof. If such trees grow on the banks of ditches, they should be kept in a pollard state, to admit of a free circulation of air.
An observation of Dr. Franklin’s deserves a place here, especially as it is not generally attended to. The opinion is indeed against it. The banks of rivers which have a quick motion, and run on a clear sandy bottom, are very agreeable and healthy situations; but the sides of rivers which have oozy bottoms, or marshy banks, or which are in the neighbourhood of extensive marshes, are to be avoided. When necessity or any peculiar advantage obliges people to build near such bad neighbours, the south side, says the Doctor, is the most eligible; because the warm southerly winds, which promote a tendency to putrefaction, and are the most frequent, blow the noxious vapors from the buildings; whereas the northerly winds, which blow but seldom compared with the former, and which generally blow strongly, check putrefaction, and speedily carry off noxious vapors.
It is now well known that the stench arising from stationary privies may be prevented by a cheap and easy method. The excrements may be received in tubs, so closely connected with the seat that no air can pass. The lower ends of the tub should be sunk below the surface of water contained in proper cisterns. The excrements are soon dissolved in water, and so carried off, every time the privy is washed, which should be as often as it is used.
In towns the stench of the common sewers is sometimes very offensive. This may be prevented by interrupting the current of air through them by means of sink-traps; the construction and utility of which are of late years well known in London. As sand or other filth may be apt to lodge in the deepened place, it should be so contrived as to be easily come at, in order to clear away every obstruction.
Let me add here to the method of correcting bad water, proposed by Dr. Munro in his Essay on the Means of Preserving the Health of Soldiers, the following easy method of keeping water clear and sweet, ascertained by several experiments made some years ago by the Society for the Encouragement of Arts, &c., in London. The method is to mix clay with the water in such quantities that when the clay is dissolved the hand immersed under the surface of the water shall not be seen. The clay subsiding, carries down with it all the impurities, and in a manner burying them, prevents their communicating any bad taste or smell to the water, which thereby continues long clear and sweet. Clay may probably correct stagnant water, and thereby preserve it clear and good in dry seasons, and may thus become very useful where there is no running water. If any bad taste or smell remains after the use of the clay, it may be carried off by one of the ventilators recommended for that purpose by the Reverend Dr. Hales. The clear water may be drawn off by a siphon or a cock, placed high enough not to touch the clay.