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will be little fear that he will be able to get a volume anything approaching the latter into his building. It is only reasonable to assume that most caretakers have little idea how many cubic feet per head per hour do get into churches or halls, but, from experience, the author is confident that 3oo cubic feet per head is much nearer the mark than even Haldane's computation. When the weather is foggy, and the air is moist and damp, the 3oo cubic feet per head per hour is a high average for churches and halls. During the spring and autumn when it is fine, and the air outside is from 5o0 to 550 F., the average may be 3oo cubic feet, and during cold weather 4oo cubic feet per head. In some mission halls, 15o cubic feet per head would more nearly represent the actual quantity when the worst conditions of weather prevail. During the first half hour of assembly the proportion of impurities is not so noticeable—it is during the last half hour of the sitting that the greatest discomfort is felt. The building is filled with nearly pure atmosphere before the audience gathers, and some time elapses before the body of air is much contaminated.
It is most desirable that the supply of air to a building should not be less than 75o cubic feet per head per hour, but this quantity cannot be obtained with comfort to the sitters unless provision, and careful provision too, has been made for warming the air introduced at the floor level before it reaches the audience. Seven hundred and fifty cubic feet per head of cold air introduced into a building, whether large or small, would mean intolerable draughts; and during very cold weather, 5oo cubic feet of unwarmed air would be unpleasant and productive of chills, colds and neuralgia to those seated near the doors, windows, or cold walls, whilst their feet would be rendered unbearably cold. Some may think that the volume of air actually supplied, namely, 3oo cubic feet per head per hour, appears small, but it is well over, rather than under stated, and, whilst calling attention to this, it is necessary to point out that the air supply mentioned has to reduce the impurity caused by the burning of illuminants, in addition to that evolved in breath. In many churches and halls the electric light has been installed, but it may be concluded, generally, that the ventilation has not been improved by the change, because the extra heat evolved by the gas and the moisture formed gave rise to a greater ventilating pressure, and caused more air to circulate than was the case after the electric light was adopted. It was inferred by the author many years ago that the moisture and organic matters in breath were the greatest impurities in the air and those which gave rise to the foul smell. This deduction was arrived at after experimenting with gas in large quantity, and after many hours burning in a building, the smell and effects were not very marked. The adoption of the electric light in churches and halls has confirmed these experiences, and the reason why the atmosphere is more stale and foul since the alteration is because less air circulates, and it is nearly, if not quite, saturated with vapour from breath.
The question arises, naturally, in reference to the churches, halls and public buildings which will be erected in future, whether it is advisable to make provision for heating and distributing as much as 3,ooo cubic feet per head per hour. The answer to this question depends much upon the kind of heating provided, and the manner in which it is proposed to introduce fresh air into the building. Still it is not necessary, nor will it be practicable, to aim at more than half that quantity, whilst if 75o cubic feet be supplied and the audience does not remain more than one hour and a half in the building there will be little complaint made of impure or bad air. In buildings where a large number sit for many hours at a stretch, a larger volume of air should be provided if possible.
Dr. Parkes concluded that the gaseous products of combustion in a building were evenly distributed, and if there were two parts per 1,ooo of carbonic acid in the air near the floor of a hall, there would be the same quatitity at the top. This result was inferred from the experiments of Lassaigne, Pettenkofer and Roscoe, but as it depends upon the quantity of aqueous vapour present in the upper portion of the air in a building as well as upon a number of physical conditions, it is wrong to assume that the carbonic acid is always equally distributed. If the upper air is saturated with moisture the carbonic acid is held in suspension in a semi-dissolved condition, but if the air is moderately dry, the carbonic acid which is at first rapidly carried upwards by the heated moist atmosphere afterwards descends quickly so that its diffusion is greatly accelerated. If the building is large the air near the floor is the purest, that under the galleries, if there are any, is the most impure, the air near the walls above the galleries has the next largest impurity, whilst in all cases, and notably in those having too much top outlet, the atmosphere in the centre of the building will be the purest. Even where the hot air furnace is used as the heating medium, if there are galleries, the air is not evenly mixed, although in consequence of the circulatory movement given to the air by this method of heating, it is approximately the case. Without galleries the admixture is much more certain. Where hot water pipes, steam pipes, radiators, or even coils of pipes are fixed above the floor of the building the movements of air are chiefly vertical, because of the more even distribution of the heating surface, and, while much preferable to the air furnace method, is equally as effective as pipes sunk below the floor, unless provision is made for fresh air to come from the outside and to be warmed before it leaves the pipes. Hot water or steam pipes fixed either below or above the floor cause vertical movements in the air, chiefly, and the vapour of the breath and that due to the burning of illuminants also greatly assists in causing an upward movement. The amount of carbonic acid may be considerable, even at a few feet from the floor
level, and in excess, comparatively, of the moisture present at that point, but at higher levels, the proportion of moisture due to respiration is more than equivalent to the carbonic acid. In other words, whilst the carbonic acid in the air of a building tends to diffuse rapidly because of its weight, the moisture from breath and from the illuminants does not mix at the same rate, the consequence being that the latter largely predominates where the air is most stagnant— under the galleries for instance—and in the upper portion of the building. It is well known that the temperature of a building occupied by a large audience is much higher in the galleries than in the centre of the floor, but once let the ah- become saturated with moisture, it is possible to find these conditions reversed if the chief supply of air comes from above in the shape of intermittent currents. Where little provision is made to introduce warm air at the floor level, and the building is heated inside, attempts to bring sufficient air from the top to keep the atmosphere breathable will be bound to culminate in intermittent currents, and up and down movements of the air. Unless the building is very high and of much larger dimensions than the seats require, so that there is a wide space next to the walls, unseated, it is fatal to comfort and good ventilation to heat the air in a building simply by radiators without any fresh warmed air being sent in.
A1r Inlets And Outlets.—In books on ventilation it is usual to calculate what size the inlets and outlets should be, and how many square inches are required for each person. The volume of air advocated for each person according to Parkes is 3jooo cubic feet per hour, and assuming that 5 feet per second is the maximum velocity allowed for the incoming air, 3o square inches is the inlet space necessary for each person. An authority on ventilation, who is usually careful and accurate, says that if the inlet air is to be introduced through the floor in a building, the area of the openings for each person must be at least 10o square inches. The idea is, doubtless, to reduce the velocity of the current of cold air coming in to about 1J feet per second, but this will not reduce the frigidity; and just imagine 3oo,ooo cubic feet of air per hour at 10° below freezing point flowing over the floor in a room holding only 1oo persons. The idea is absurd in the extreme, and it is sheer nonsense to advocate the introduction of such a volume of cold air into a building seated up to the walls and occupied by an audience.
The Education Department advise, for public schools, that z\ inches be the minimum air inlet space for each scholar. This is a sensible allowance, and it is not advocated that the air shall be unwarmed either. In justice to the profession, it is necessary to add that in my experience no architect has ever attempted to provide 3o inches of inlet space for each person; and it is best, perhaps, to calculate what this allowance would mean if put into practice. A church is 1oo feet long and seats 6oo persons. The windows are nearly air-tight, and the doors close fitting, so that less than 6o,ooo cubic feet per hour get through them. This allowance is a high average for churches whose windows are for the most part air-tight. The remaining inlet air for the church is to be provided by Tobin shafts, which to simplify calculation are 12 inches by 5, or 6o square inches in area. To afford the inlet space mentioned above, it will be necessary that the Tobin shafts should touch each other throughout the whole length of both sides of the building—i.e., 2oo feet—and that there should be, in addition, 8o feet run of Tobin shafts at the ends.
It is generally assumed either that the area of the outlets ought to be greater than that of the inlets, to allow for the friction of the out-going air, or they are advocated to be of similar area, and not to exceed 12 inches square each opening. Taking the example already given of a building 1oo feet long, it would not be possible to get the 12 inch