Upon commencing our business, we all admired the comfort of the room; but as time went on, most of the company began to complain of a little draught on the head and back of the neck. The draught, which at first was only a suspicion, became a certainty, and in another hour or so, by the time our business was over, notwithstanding a screen placed before the door, and a blazing fire, we were delighted to make a change to the comfortable dining-room, which communicated with the room we had just left by means of folding doors, closed with the exception of just sufficient space left at one end of the room to allow a waiter to pass in and out. Very curiously, before the soup was finished, we became aware that the candles which assisted the electric glow lamps (merely for artistic effect) began to flare in a most uncandlelike manner—the flames turning down, as if some one were blowing downward on the wicks; and at the same time the complaints of "Draughts, horrid draughts!" became general, and from every quarter. Finding that, as the dinner went on, the discomfort became unbearable, even although the doors were shut and screens put before them, I gave up dining, and took to scientific discovery. The result of a few moments' observation induced me to order "those gas jets," which I saw peeping out from among the foliage of the electroliers, to be lighted up. In two or three minutes the flames of the candles burned upright and steadily, and in less than ten minutes the draughts were no longer felt; in fact, the room became really comfortable.
The reason of the change was simple. The stratum of air lying up at the ceiling was comparatively cold. The column of heated air from the bodies of the twenty guests, joined to the heat produced by the movements of themselves and the waiters, together with the steam from the viands and respiration, displaced the colder air at the ceiling, and notably that coldest air lying against the surface of the glass. This cold air simply dropped straight down, after the manner of a douche, on candles and heads below. The remedy I advised was the setting up of a current of hotter steam and air from the gas burners, which stopped the cooling effect of the glass, and created a stratum of heated steam and air in slow movement all over the ceiling. The effect was a comfortable sensation of warmth and entire absence of draught all round the table. Later on, to avoid the possibility of overheating the room, the gas was put out, and the electric lights left to themselves. But before we left, the chilliness and draughts began to be again felt.
The incident here narrated occurred at the end of the month of April last, when we might reasonably have hoped to have tolerably warm nights. It is therefore clear that in this instance neither electricity nor candles could effectually replace gas for lighting purposes. They both did the lighting, but they utterly failed to keep the currents of air steady. I have always remarked draughts whenever I have remained any length of time in rooms where the electric light is used. On a warm evening the electric light and candles would undoubtedly have kept the room cooler than gas, with the same kind of ventilation; I do not think they would have put an end to cold draughts. This the steam from the gas does in all fairly built rooms.
It is a well-known fact that dry air parts with its relatively small amount of specific heat, in an almost incredibly rapid manner, to anything against which it impinges. Steam, on the contrary, from its great specific heat, remains in a heated state for a much longer time than air. It is not so suddenly reduced to a low temperature, and in parting with its own heat it communicates a considerable amount of warmth to those bodies with which it comes in contact. Thus the products of the combustion of gas (which are principally steam) serve a useful purpose in lighting, by keeping at the ceiling level a certain stratum of heated vapor, which holds up, as it were, the carbonic acid and exhalation from the lungs given off by those using the room. The obvious inference, therefore, is that if we take off these products from the level of the ceiling, we shall take off at the same time the impure and vitiated air. On the other hand, if we make use of a system of artificial lighting, which does not produce any steam, then we shall have to adopt means to keep the air at the ceiling level warm, in order to prevent the heated impure air from descending in comparatively rapid currents, after having parted with its heat to the ceiling. It may very frequently be observed on chilly days that a number of currents of cold air seem to travel about our rooms, although there may be no crevices in the doors and windows sufficient to account for them; and, further, that these currents of cold air are not noticed when the curtains are drawn and the gas is lighted. The reason is that there is generally not enough heat at the ceiling level in a room unlighted with gas to keep these currents steady. Hence the complaints of chilliness which we constantly hear when electric lights are used for the illumination of public buildings. For example, at the annual dinner of the Institution of Civil Engineers, held at the end of April last in the Conservatory of the Horticultural Gardens, the heat from the five hundred guests, and from an almost equal number of waiters and attendants, displaced the cold air from the dome of the roof, and literally poured down on the assembly (who were in evening dress) in a manner to compel many of them to put on overcoats. If the Conservatory had been lighted with gas suspended below the roof, this would not have been the case, because sufficient steam would have been generated to stop these cold douches, and keep them up in the roof. In fact, if electric lights are to be used in such a building, it will be necessary to lay hot-water pipes in the roof, to keep warm the upper as well as the lower stratum of air, and thus steady the currents.
Having pointed out difficulties which arise under certain conditions of the atmosphere in rooms built with care, to make them comfortable when electric lighting is substituted for gas, I will lay before you some few particulars relative to the condition of small rooms of about 12 ft. by 15 ft. by 10 ft., or any ordinary room such as may be found in the usual run of houses in this country. The cubical contents of such a room equals 1,700 cubic feet. If the room is heated by means of a coal fire, we shall for the greatest part of the year have a quantity of air taken out of it at about 2 feet from the floor by the chimney draught, varying (according to atmospheric conditions and the state of the fire) from 600 to 2,000 or more cubic feet. This quantity of air must, therefore, be admitted by some means or other into the room, or the chimney will, in ordinary parlance, "smoke;" that is, the products of combustion, very largely diluted with fresh air, will not all find their way up the flue with sufficient velocity to overcome the pressure of the heavy cold air at the top of the chimney. If no proper inlets for air are made, this supply to the fire must be kept up from the crevices of the doors and windows. In the line of these currents of cold air, or "draughts" as they are usually called, it is impossible to experience any comfort—quite the contrary; and colds, rheumatism, and many other serious maladies are brought on through this abundant supply of fresh air in the wrong way and place.
According to General Morin (one of the best authorities on ventilation), 300 cubic feet of air per hour are required for every adult person in ordinary living rooms. Peclet says 250 cubic feet are sufficient; less than this renders the atmosphere stuffy and unhealthy. It is generally admitted that an average adult breathes out from 20 to 30 cubic inches of steam and vitiated air per minute, or, as Dr. Arnott says, a quantity equal in bulk to that of a full-sized orange. This vitiated air and steam is respired at a temperature of 90° Fahr.; and therefore, by reason of this heat, it immediately ascends to the ceiling, together with the heat and carbonic acid given off from the pores of the skin. This fact, by the bye, can be clearly demonstrated by placing a person in the direct rays from a powerful limelight or electric lamp, and thus projecting his shadow sharply on a smooth white surface. It will be observed that from every hair of the head and beard, and every fiber of his clothing, a current of heated air in rapid movement is passing upward toward the ceiling. These currents appear as white lines on the surface of the wall; the cause probably being that the extreme rarefaction of the air by the heat of the body enables the rays of light to pass through them with less refraction than through the denser and more moist surrounding cold air. An adult makes, on an average, about 15 respirations per minute, and therefore he in every hour renders to the atmosphere of the room in which he is staying from 10 to 15 cubic feet of poisonous air. This rises to the ceiling line, if it is not prevented; and thus vitiates from 100 to 150 cubic feet of air to the extent of 1 per cent, in an hour. General Morin thought that air was not good which contained more than ½ per cent, of air which had been exhaled from the lungs; and when we consider how dangerous to health these exhalations are, we must admit that he was right in his view. Therefore in one hour the 15 foot by 12 foot room is vitiated to more than 2 feet from the ceiling by one person to the extent of ½ per cent., and it will be vitiated by two persons to the extent of 1 per cent, in the same time.
It must be remembered here that the degree of diffusion of the vitiated air into the lower fresh air contained in the remaining 8 feet of the height of the room depends very materially on the difference of temperature between these upper and lower strata and the movements of air in the room. The heavy poisonous vapors and gases fall into and diffuse themselves among the fresh air of the lower strata—very readily if they are nearly the same temperature as the upper, but scarcely at all if the air at the ceiling line is much hotter. Hence it occurs that, in warmed rooms of such size as I have mentioned, where one or two petroleum lamps are used for lighting them, after two or three hours of occupation by a family of three or four persons in winter weather, the air at the ceiling line has become so poisonous that a bird dies if allowed to breathe it for a very short time—sometimes, indeed, for only a few minutes. With candles, if the illumination of the room is maintained at the same degree as in the case of lamps, the contamination of the air is very much worse. It is doubtless the case that poisonous germs are rapidly developed in atmospheres which are called "stuffy;" and although, in a healthy state of the body, we are able to breathe them without perceptible harm, yet even then the slight headache and uneasiness we feel is a symptom which does not suffer itself to be lightly regarded, whenever, from some cause or other, the general condition is weak.
The products of combustion from coal gas (which are steam and carbonic acid mixed with an infinitesimal quantity of sulphur) are, proportionately, far less injurious to animal life than the products from an equal illuminating power derived from either oil or candles. They are, however, it is certain, destructive to germ life; and therefore, if taken off from the ceiling level, where they always collect if allowed to do so, no possible inconvenience or danger to health can be felt by any one in the room. But in our endeavors to take off the foul air at the ceiling, we encounter our first serious check in all schemes of ventilation. We draw the elevation and section of the room, and put in our flues with pretty little black arrows flying out of the outlets for vitiated air, and other pretty little red arrows flying in at the inlets; but when we see our scheme in practice, the black arrows will persist in putting their wings where their points ought to be; in other words, flying into instead of out of the room.
One of the best ways of finding the true course of all the hot and cold currents in a room is to make use of a small balloon, such as used to be employed for ascertaining the specific gravity of gases; and, having filled it with ordinary coal gas, balance it by weights tied on to the car till it will rest without going up or down in a part of the room where the air can be felt to be at about the mean temperature, and free from draught. Then leave it to itself, to go where it will.
As soon as it arrives in a current of heated air, it will ascend, passing along with the current, and descending or rising as the current is either warm or cold. The effect of the cold fresh air from windows or doors, as well as the effect of the radiant heat from the fire, can be thus thoroughly studied. Some of our pet theories may receive a cruel shock from this experiment; but, in the end, the ventilation of the room will doubtless be benefited, if we apply the information obtained. It will be discovered that the wide-throated chimney is the cause of the little black arrows turning their backs on the right path and our theoretical outlets for vitiated air becoming inlets. The chimney flue must have an enormous supply of air, and it simply draws it from the most easily accessible places. From 1,000 to 2,000 cubic feet of air per hour is a large "order" for a small room. Therefore, until we have made ample provision for the air supply to the fire, it is quite useless to attempt to ventilate the upper part of the room, either by ventilating gas lights or one of the cheap ventilators with little talc flappers, opening into the chimney when there is an up draught, and shutting themselves up when there is any tendency to down draught. The success of these and all other ventilators depends upon there being a good supply of air from under the door or through the spaces round the window frames. These fresh air supplies are, of course, unendurable; but if one of the spaces between the joists of the floor is utilized to serve as an air conduit, and made to discharge itself under the fender (raised about two inches for the purpose), quite another state of things will be set up. Then the supply of air thus arranged for will satisfy the fire, without drawing from the doors and windows, and at the same time supply a small quantity of fresh air into the room. But the important fact that the radiant heat from the fire will pass through the cold air without warming it all must not be lost sight of. In reality, radiant heat only warms the furniture and walls of the room or whatever intercepts its rays. The air of the room is warmed by passing over these more or less heated surfaces; and as it is warmed, it rises away to the ceiling. Therefore, if we desire to warm any of this fresh air supplied to the fire, it must be made to pass over a heated surface. The fender may be used for this purpose by filling up the two inch space along the front, as shown in the drawing, with coarse perforated metal. This will also prevent cinders from getting under it. It will be found that for the greater part of the year the chimney ventilator and the supply to the fire will materially prevent "stuffiness," and keep those disagreeable draughts under control, even although the room be lighted with a 3 light chandelier burning a large quantity of gas.