# Popular Science Monthly/Volume 1/July 1872/Ventilation, and the Reasons for it

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* VENTILATION, AND THE REASONS FOR IT.
By ROBERT ANGUS SMITH, Ph. D., F. R. S.
IT is often asked how much fresh air we must allow to come into a room in order to keep it wholesome. The amounts vary so much that we shall never be able to answer the question as it arises in all its changes, unless we consider our reasons for ventilating.
The first is certainly the dislike to organic-smelling substances evaporated from living beings. As some of them are very volatile, a very little rise of temperature increases their amount; and, in warm weather, we require a change of air so frequently, that we cannot make any use of the carbonic-acid test. The amount of change is infinite; we require it for every breath, and we do not consider whether a door is sufficiently open; we open all doors and windows, or leave the house entirely.
Let us take the other extreme—a very cold room—an Esquimaux ice-hut. The amount of air wanted is wonderfully small; we do not know how much the carbonic acid may rise, but it must be very high. The organic matter is frozen, and is probably condensed on the ice; it may be inhaled as a solid, and in a form not to affect the smell. For a similar reason we require less ventilation in cold weather: it is not foolish, as some will endeavor to persuade us, to take less, but it is a natural instinct. We object to the cold, and we learn that heat is a more pressing want than even pure air, whether the organic matter affects our senses or not.
The next reason for ventilating is allied to the first; we say it is to produce freshness. This means that, although all the air of the room be quite new, it has received a something from the surfaces in the room which must be cleared out. This is the reason that housewives like to keep the doors and windows open, and allow the air for a time to blow through the house. This process removes the last particles from the furniture, and is that finish which polishing cannot give. If ​the undefined impurity exists in large quantities, only rubbing can remove it rapidly, and this is done when we clean thoroughly walls and furniture. If very bad, and time presses, while elegance is not a demand, we cover the whole, and find whitewashing to be a ready mode.
The other reasons for ventilating have arisen from scientific inquiries. We wish to remove the carbonic acid; we might be able to find this gas by the senses, if it were very abundant; but it, is not so as a rule, until after our senses have informed us of the organic accompaniments. It furnishes, however, one of the most important and probably the most important of the reasons in every-day life, because carbonic acid is the most rapidly hurtful to animal life of all the emanations from the person. It lowers the vitality rapidly, and kills with indefinite warning. The best warning is the organic matter, which acts for both. The warning by carbonic acid is called indefinite, because people lose vitality, but do not observe that the cause is in the atmosphere, there being no smell connected with that gas. At night, when lights are burning, the carbonic acid warns better than the other impurities, by simply putting out the candles. This seldom occurs in private houses, but dim burning is common enough. Mr. James Napier, F. C. S., tells me that he has seen the candles beginning to go out in a small meeting-room in the country, which had a low ceiling and was crowded. It was needful to keep the door open. How blunt, then, is our perception of carbonic acid!
Another reason for ventilating is to remove solid floating bodies, including infectious matter, fungi, and peculiar emanations arising from disease or other anomalous conditions. These floating bodies can sometimes be distinguished by the sense of smell—in the case of mould, for example. If it were possible to describe a smell completely, this class would be largely subdivided, since experience has made many persons very learned on this subject. It is, however, a knowledge which we have not yet been able to receive from or communicate to others. This whole question requires careful examination. The knowledge of the smell cannot be taught, but it may guide us to much that can be taught. Ventilation for this class of bodies will be probably much more attended to in future; care must be taken to drive them to the nearest opening, and not to allow them to diffuse themselves through the room in which they may be produced. In some cases resort must probably be had to rapid artificial and heated currents.
We ventilate to remove smoke and ordinary dust; these are easily seen; and we use ventilation to procure dryness. Moisture rises constantly from the skin, and, if an inhabited apartment is not ventilated, that moisture accumulates. By opening the windows we cause floors to dry sooner, and we remove moisture from all the apartments, and that moisture has generally organic matter with it. If we ventilate with very moist air, we shall dry nothing; if we have very dry air, we may dry too thoroughly. It is, however, better for us to have what is ​called practically dry air—that is, air capable of containing much more moisture than it has. The amount of drying work done is according to the dryness, warmth, and speed of the air; with little of these qualities, a great bulk of air is required, where otherwise a small bulk might have sufficed. By warmth and dryness we have an advantage in requiring less rapid currents. I have said elsewhere that a climate has a certain advantage from being very rainy. To call dryness an advantage is not a contradiction. When rain falls and washes the air, we can feel the benefit; when the substances floating in the atmosphere are dried up, we can imagine the advantage; but when the air is kept loaded with moisture which does not fall as rain, and is not carried off by wind, we can easily understand why the results should be hurtful. That it is not the watery vapor itself that injures may be learned from dye-houses, where men spend their lives in all conditions of dampness, sometimes in steam dense enough to make it difficult to see to the distance of a yard. There they have not the heavily-laden moisture of hot, damp climates with rich vegetation, and they have abundant warmth, so that the moisture is not used for absorbing heat and producing colds.
The demands of ventilation would best be explained if we could reply to these questions: What is the smallest amount of carbonic acid which may be call injurious? and what is the smallest amount of organic matter?
The amount of carbonic acid in the air is under .04 per cent, in places that are healthy, but not above .032 in the most open and healthy places. About five times that amount affects a candle sensibly, a photometer being used, and it is extremely probable that less affects it also. Are human beings affected as readily? I rather avoid this question at present; we have not facts enough. We will now speak of the gas in conjunction with organic matter.
Let us take, the two together, and we then find that much depends on the temperature also. If the day be warm, we may pass from a room having .06 in a hundred of carbonic acid to the air with .03, and feel refreshed. If the day is not warm, we do not feel the difference; at least, such persons as I have examined do not. The conclusion is that, in the early stages of the want of ventilation, the organic exhalations are the most injurious. Now, these increase with the temperature, while the acid does not. For this reason we ventilate in warm weather for the organic matter far more than for the sake of the acid. As the former has not hitherto been estimated by weight, we may view the subject only in relation to the carbonic acid. I think it probable that we shall be able to view it also in relation to other substances. For example, so much temperature will represent so much organic exhalation, and the volume of air will differ accordingly.
When the ventilation is desired to be very good, the amount required when pure air is supplied is much less than with imperfect air. ​As the demand becomes less, the difference diminishes. If ozone were taken into consideration, the difference would probably be much greater; but I do not know what allowance to make for that body, and leave it out of consideration. In the smoky towns there is none at all.
The conclusion has been drawn by some scientific men that in all spaces, and under every circumstance, the same amount of air must be supplied. Now, it is true that the same amount is to be actually breathed, and, if this breath is thoroughly mixed with all the air of the room, the same amount must be supplied for ventilation, whatever the size of the room. But let us suppose—the most common case—that the thorough mixing does not take place, and we have at once a different amount of air required.
As to the imperfect mixing, it is so various and characteristic that we cannot reduce it to rules; we may hold a smoking substance in the midst of an apartment, and find the smoke go directly to an opening without mixing with the air of the room. It goes, too, with a velocity greater than that of the air of the room, otherwise an opening must be supposed sufficient to change the whole air of the room in a few seconds, that being the time required for the smoke to reach the opening. If we could drive the impure air in a similar way in a narrow current toward its exit, we might manage ventilation with a very small amount of air. To do this is a matter of great importance, because the expense of building is becoming so great, that very few men can afford to pay for a large enough house, and, while rents are rising, the rooms of the middle classes have actually diminished in some places, and within these few years. Yet the evil of small rooms is great, because rapid currents are required for ventilation; cold currents are hurtful, and the warm difficult to obtain. If, however, we could obtain warm-air currents, it would not be important for us to have the rooms so large. It is a question of price. I believe the warmth must be obtained as the first demand of Nature, and without it civilization will go back. When men are cold, they give themselves to physical exercise, and, if that is impossible, to discomfort, in which the mind refuses to do more than to complain, if it cannot forget. Which is cheapest for us? Is it to build large rooms and to have less warmth with slow currents, or to build small rooms and to have more warmth with rapid currents? It is to be wished that the former should be the rule for private houses; more comfort and convenience are promised, and mechanism is not required; if it were, it could not be obtained. For hospitals, the use of mechanism is more within possibility. The expense of large rooms, when the architecture is of a kind intended to ornament a capital city, is very great. Should we not gain by a judicious system of warming? Our methods of warming are very cumbrous, and we seem to be behind ancient Rome and modern Russia. We warm the air which changes in a moment when a door ​or window is opened, and we do not warm the house itself. Builders make the walls thinner in these days, and we sit at a fire very much as savages do over a blaze in the open air.
This is less the case with large rooms, where we require slower currents. We may next ask, Is there any advantage in rapid currents at any time? There is; in the case of infectious diseases, it would seem in the abstract to be of the greatest importance that the patient should be in a current, speaking as a chemist, and not a physician. The first reason is for his own sake. Even in health we poison ourselves, and in disease we tend more rapidly in the same direction. Infectious emanations may be collecting round a patient, and, if so, the still air will keep them more carefully near him. I speak only generally, and do not enter on the hospital controversy.
Perhaps we cannot have rapid currents in large rooms very easily, so much air is required; but we can have frequent changes of air. It is clear, however, that the rapid removal of the air collecting around patients with infectious diseases, and probably also non-infectious, is most likely to promote health, both in the patients and in the attendants. Few people can stand the rapid motion of cold air, and, if we must have rapid currents, they must be heated.
The source of the air with which we ventilate ought probably to be high in all cases, but even here we must move slowly. We are not quite sure that any infectious disease ever sends its emanations high into the air. Disease seems to creep along the ground; the causes may be at a considerable height, but we are compelled to suppose them very thinly disseminated there; and the action seems to be according to quantity as well as intensity; toward the surface they congregate and are active. This we see from the evening air, especially in marshy places; it is only after a certain repetition of the attack of the more thinly diffused wandering substances falling down from the atmosphere and accumulating, that men yield to the influence. As a rule, it would be unnecessary to purify the air of the daytime, if in an open place, even in average towns; and in most places it would be unnecessary to purify the air of the night in this country. It would, however, be better to warm it in northern and damp climates, and even in temperate climates, in order to produce a difference of temperature between the air entering the room and that within it, even if the necessity arising from the cold of rapid ventilation did not occur. In inhabited rooms the moisture increases as much as the organic matter, and the condition of the air is similar to that of the evenings of summer: whenever the temperature goes down a little, there is a deposit of dew; but, when the warmth increases, the air is laden with moisture, and the condition resembles that near a warm close vegetation. In both cases ventilation is wanted. Our walls become saturated with moisture if they are porous, if not porous they are covered with streams of water. The moisture has organic matter in it which ​is not removed by mere drying, and the effects are very long in leaving. We may know this from breathing the air of any bedroom in a London hotel, or in most private houses in towns. People are afraid to keep their windows open, because of the smoke without, and so they retain the organic matter. We can readily smell this, even if arising from healthy persons, and it has ceased to be a matter of surprise. If unhealthy persons are present, unhealthy matter may be expected to diffuse.
If, then, any disease is propagated by organic germs living on the organic matter of the atmosphere, or associated with it, it is not at all wonderful that the disease should lurk in corners of houses, in clothes, or other porous matters, simply because we can trace floating matter to its lodgment in such places.
It is remarkable how readily porous bodies absorb the moisture of the air, and substances with it. I find that the leather on the bookcases in my study, where gas has been used, is made rotten, and in exact proportion to the height, the highest being so frail that it can scarcely be handled, while the lowest is still pretty firm, although much less so than at first. The amount of sulphuric acid in the pieces is also in proportion. The intermediate are affected in an intermediate way. No better proof can be had of the absorptive action of these porous substances, and of the unequal state of the atmosphere in various parts of a room.
When rooms which have absorbed organic matter have been shut up, the original peculiar smell ceases, and a musty one takes its place; we recognize something which instantaneously brings that of mould to our minds. We cannot doubt that the air in such cases is full of the spores of such plants; the plants themselves grow in abundance, and we know well that when they grow they readily send out colonies. The leather of the bookcase was said to show the inorganic bodies; the books themselves are covered with the organisms when care is not taken, so that one small room gives an epitome of the whole subject. We have here, therefore, no mysterious agent, but one that is perfectly plain. Why should the agent be mysterious in the case of the infectious disease? It is only so far a mystery—we do not know the different plants or organisms, and so cannot tell whether we have health or disease in them by merely examining them through a microscope.
If porous substances have the characteristics alluded to, why use them? There are some difficulties here. If a wall is to be cleaned frequently, and rubbed when wet, it is better that it should not be porous. That seems quite clear; but when these processes cannot be undertaken, it really seems as if it were better to have it porous. Such substances absorb moisture in some seasons, and give it out slowly at others. Our clothes are of this kind. It is not possible to have warm coverings not porous. Porous bodies hold also a good deal of air, and they cause oxidation more readily. Nature has employed them for ​disinfection more than any others. The whole soil of the earth is a great disinfectant, kept in constant activity, being constantly required, holding; in itself the most nauseous and unwholesome things, and still having healthy people living over it. However, the soil may be too full, and at times it becomes so, and therefore we run to places which cannot contain much impurity, such as bare rocks; and in such places we obtain pure air. If in houses we have too much organic matter for the porous substances to oxidize, we must resort to non-porous surfaces; but then they must, like the rocks, be often washed, or excessively exposed to the air or the warm sun.
To purify rooms the air must blow long into them, or every part must have the organic matter rubbed off by the hand. This is a sufficient rule for both hospitals and private houses. Good rubbing will purify furniture, and this our housewives know; long-continued currents of air are also known to be good, but better as a supplement to rubbing. The rules are very easy chemically, but mechanically they are difficult. This is merely a repetition of that which has been said elsewhere, and long ago, although it is here stated in other words. The world must be told every thing in ten thousand different ways before it learns, and it is wearisome to repeat the lesson. I am only saying, also, what every clean house-keeper carries out; and yet there is an apparent novelty in it when we compare it with the sayings and doings of many persons, intelligent and observing although they be.—Air and Rain.