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of which .75× 960,000 720,000 cubic feet an hour, or 200 cubic feet a second, will be carried off at the ceiling, and .25x960,000 = 240,000 cubic feet an hour, or 67 cubic feet a second, by the openings near the As the velocity of discharge near the ceiling may be as high as 3 feet a second, the openings to be made there-as far as possible directly above the main chandelier-should have—

200

3

=67 square feet of clear passageway,

deduction being made for solid parts; and the velocity of draught near the floor being also 3 feet a second, the corresponding openings should bave a clear area of―

67
3

= 22 square feet.

The grating in use has an area of but 116 square feet of total surface, including solid portions, and scarcely presents 43 square feet of clear passage.

Above the openings in the ceiling should be placed external ventilators, having together the same clear area, which will increase the velocity of discharge.

In regard to the ventilating openings at the floor-level, they may easily be made around the contour of the rooms under the steps on which the seats are placed; and their pipes should be carried in the piers of the vaults of the lower vestibule to the cellar, where they should join the collecting passages terminating in a general ventilating-chimney, at the bottom of which a coal fire or a number of gas-burners should be kept burning.

The dimensions of these pipes should be calculated by the general rules previously given. If there are serious difficulties in the way of producing this down-draught, an up-draught may be used, produced by the aid of gas-burners placed in vertical flues made in the thickness of the walls.

119. Introduction of air.-But it is not sufficient merely to secure the discharge of the foul air; it is necessary to provide for the admission of an equal amount of fresh air at proper temperature.

This air, which in winter should be warmed to a temperature of about 680, may be admitted through an interjoist in the balcony, which is 20 feet above the floor. It should flow horizontally below the chandeliers, above and away from the occupants, and its horizontal velocity of admission may, without inconvenience, be 3 feet a second. Its volume being 954,000 cubic feet an hour, or 265 cubic feet a second, the total sectional area of the interjoist and of the conducting passages should be 81 square feet.

The length around the inner edge of the balcony being about 200 feet, it will suffice to give the openings

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but on account of the ornaments which break up the passage it will be necessary to make them 10 inches either in height or in developed profile. These arrangements will insure the renewal of 954,000 cubic feet of air an hour, or 1,590 cubic feet to each person, if there are 600 present, sufficient in all seasons to secure the healthful condition of the room and to moderate its temperature; but it is not necessary that they be isolated and confined to one of the reception rooms of the palace. It will be equally necessary to adopt similar arrangements for the two adjoining rooms, which often contain many persons, and also for the large gallery, frequently used as a ball room. It may not be unnecessary to add that for evening parties the two large fire places which are in the grand gallery may, by means of gas-burners placed within them, serve as ventilating-chimneys; and if there is any difficulty in cutting in the side-walls descending flues leading to the basement, ascending flues may be made, separate, or communicating with a single ventilator placed in the roof over each room.

The fresh air should enter above the cornice, and in a horizontal direction.

Each of the principal saloons in the palace should thus have its own ventilators provided with regulating-valves; they should be independent of the others, and this will prevent the unpleasant currents which would otherwise arise as the guests take their departure.

HALLS OF ASSEMBLY AND LECTURE-ROOMS.

120. These places of temporary resort, where there is often more than one person to every square foot of floor-surface, should be ventilated at the rate of 1,000 cubic feet of air an hour to each person.

The arrangements which I have adopted for the main lecture-hall of the Conservatory of Arts and Trades, and of which the satisfactory results have been seen every day for five years, appear to me worthy of imitation.

The foul air is drawn off through openings in the risers behind the feet of the auditors, and their total clear area for the passage of the air -deduction being made for the solid portions of the grating, if there are any-should be calculated so that the air will only attain a velocity of 28 or 30 inches a second. This surface also should be distributed as uniformly as possible among the steps.

The basement under the lecture-room, kept as clear as possible, should communicate with a ventilating-gallery, placed underground or at the ground-floor level if possible, the sectional area of which should be calculated so that the velocity of the air shall not be greater than 4 feet a second.

This gallery should terminate in a ventilating-chimney, the mean section of which should be determined on the condition that the velocity of the air shall reach 5 or 7 feet a second in order to secure the permanence of the current.

At the foot of this chimney, a grate, separated from the walls and placed about 3 feet above the ground, should contain a coal-fire, which will give to the draught the necessary strength. Experiments show that with proportions about equal to those that have been mentioned, 140,000 to 160,000 cubic feet of air an hour can be carried off from a well-filled lecture-room to every pound of coal burned. On the preceding data, the number of pounds of coal to be burned may be calculated from the number of persons in attendance, allowing to each 1,000 cubic feet of air an hour, and the surface of the grate may be determined on the condition that each square foot is to consume 4 pounds an hour, which corresponds to a slow fire.

Doors and valves should be placed in this gallery to check the motion of the air as required.

If in the lecture-room substances that give off bad smells are produced, ventilating-pipes should be arranged under the furnaces, or under the table, which should be 2 or 3 square feet in sectional area, and prolonged, if desired, directly to the chimney instead of terminating in the gallery. The openings of these pipes in the furnace or in the table should be closed whenever it is not necessary to use them.

121. Admission of fresh air.-Generally it will be well, when the construction permits, to make the air flow in through the roof over the lecture-room, which should in that case be close and ceiled, or in an interjoist, whence it will descend into the room through openings uniformly spread over the surface of the ceiling.

When this arrangement can be adopted, the clear surface of the openings should be calculated on the condition that the air should pass through them with a velocity of about 20 inches a second.

In the main lecture-room of the Conservatory, where the amount of air admitted rarely exceeds 636,000 cubic feet an hour, or 177 cubic feet a second, this condition would require a clear area for the fresh-air openings of 108 square feet. They actually have an area of 129 square feet.

If it becomes necessary to admit the fresh air through one or more of the walls of the room, opposite walls should be preferred and the openings should be placed as far as possible from the audience, fitting guides to them to force the air to follow the flat or curved surface of the ceiling, so that its entering velocity, which may then be as great as 40 inches a second, may be gradually reduced before it reaches the audience. The air brought in should have in winter a temperature lower by 4 degrees than that which is to be maintained in the room, which should be about 68°.

For this purpose, the warm air from the heating-apparatus should be mixed in a separate chamber with the cold air taken from outside through a convenient opening. The action of the draught will serve to draw in this cold air, which should be made to flow into the mixingchamber above the warm air.

Valves should be arranged to regulate the amounts of hot and cold air so as to give a proper temperature to the mixture.

When the lecture-room is not occupied, it will be well to close all the communications with the ventilating-chimney, the mixing-chamber, and the fresh-air openings, in order to avoid reversed draughts which would cool the interior.

The intermittent use and heating of lecture-rooms causes a much greater expense for fuel than if they were constantly occupied.

These places also being only ventilated when they are in use, it is well to reserve means of warming through special openings different from those which are used in connection with ventilation, the openings to be afterward closed.

The mean results for heating and ventilating lecture-rooms arranged similarly to those in the conservatory will be as follows:

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Large reception-rooms, such as those of legislative halls, should be warmed and ventilated upon the same principles.

In all cases, it should be remembered that staircases, vestibules, &c., which give access to these places with strong ventilating-draughts, should be warmed without being ventilated, and kept at a temperature a little above that of the main room, so that the occasional opening of doors will only admit warm air, which would not be unpleasant.

Experiment has shown at the Conservatory that, when these places are thus heated and kept closed, they form a sort of air-lock, and the velocity with which the air enters through the doors, which being opened put them in communication with the interior of the lectureroom, is barely one foot a second, and consequently almost insensible, especially if the temperature of the air is at least equal to that in the main room.

THEATERS.

122. A theater is composed of three principal parts1. The stage and its accessories.

2. The auditorium, waiting-rooms, and dependencies. 3. The vestibules, staircases, and business-offices.

The stage, the flies, and the corridors which lead to the dressing-rooms and green room should be kept at a temperature of 640 to 68° in winter. Generally, the latter places will not require to be ventilated, as they contain but a small number of people, occupying a large space. Still, as the green-room and the rooms in which the chorus rehearses often contain a large number of artists, it may be necessary in certain cases to ventilate them. The upper portions of the stage are often raised to a high temperature on account of the heat produced by the lights, by the

fire in spectacles, &c., which requires that special precautions be taken to air them and to remove the hot gases.

The auditorium and the waiting rooms are the parts in which it is especially desirable to maintain salubrity, change of air, and a moderate temperature. The amount of air to be changed an hour to each spectator should be 1,400 cubic feet, and it is well to reserve means of increasing it to 2,100 cubic feet during the summer.

The heating may be effected either by means of hot-air heaters with sufficiently large mixing-chambers, as has been previously mentioned, or by hot-water apparatus, of which the first cost need not be greater than the preceding, while it will be very easy to regulate.

123. Air-supply.-The fresh air should be taken, if possible, from the neighboring gardens, far from dwelling houses, or from court-yards, or by special chimneys, drawing it from the top of the edifice. Care should be taken that these chimneys should be as far as possible from the ventilating-chimneys, and that their tops be not as high as the ventilating chimneys, in order that they may not reverse the draught.

If fresh air be introduced by subterranean passages, the walls, the vaults, and the floor of these passages should be made of hydraulic masonry, perfectly tight, and nothing should be done to them by the custodians of the building, except to examine their state of cleanliness. 124. Admission of air.-The air should be carried into the auditorium: 1. By interjoists, formed between the floor of one gallery and the ceiling of that below; the air should issue horizontally from the whole circumference of the interjoists, which should be at least 5 or 6 inches in clear height.

It may be assumed that the horizontal velocity with which it flows out will be 3 feet a second; but it is necessary to take care that the openings through the gratings which terminate the interjoist-spaces have at least a surface corresponding to this velocity, and that none of these openings be placed horizontally above the spectators of the lower tier of seats.

2. By openings arranged at the height of about 10 feet in the walls separating the stage from the auditorium; and there may also be formed there a chamber for mixing the warm air from the heaters with the cold air from outdoors.

3. By auxiliary pipes, intended especially for summer-ventilation, arranged, if possible, under the floors of the corridors of each gallery. They should take air from outdoors, and their section should be calculated, so that the velocity of passage shall not exceed 2 feet or 28 inches a second. All these pipes should be supplied with valves to close them when required in cold weather.

125. Necessary precautions.-Ventilation, by drawing out the foul air, necessarily causing the entrance of fresh air, it is necessary to see that the opening of doors does not occasion unpleasant currents. For this purpose, corridors, passage-ways, and staircases should be heated in

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