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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 24 or 3 square feet in sectional area, and pro. longed, 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 con. struction permits, to make the air flow in through the roof over the lecture-room, wbich 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 open. ings should be calculated on the condition that the air should pass throngh 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, wbich 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 680.

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 mixing. chamber above the warm air.

Valves should be arranged to regnlate 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:

5 For heating—to 1,000 cubic feet conConsumption of coal tent .......

....... 2-21 lbs. in 12 hours. For ventilation—to 1,000 cubic feet

of air renewed ...................4-1 lb.

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 bas 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 lecture. room, 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 parts-
1. 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 680 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 especi. ally 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 pone 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

winter to a temperature of about 680. The doors of adjoining boxes being usually contiguous, it will be well to place a hot-air opening in the corridors before each pair of doors, so that during the momentary opening of one of these doors warm air may enter into the correspond. ing box. The same plan may be carried out by each door in the pas. sage-way ; but it is necessary that these hot-air openings be placed in vertical planes, and not at the floor-level. The passage-ways should have two doors opening outward and inward, and between them should be a hot-air opening.

126. Removal of foul air.—This air should be drawn out of the room by ventilating.openings at the back of the boxes or galleries, or in the risers of the amphitheater. The clear surface of these openings should be calculated on the condition that the air shall enter with a velocity of 28 or 30 inches a second.

Each box or each pair of adjoining boxes of the same tier should have a special ventilating-pipe. The section of these pipes should be calcu. lated on the condition that the air drawn out should have a velocity of 3 feet a second. For the first, second, and third galleries, these pipes should be carried to the ventilator above the chandelier.

For the parquet, the orchestra, and the lower boxes, and, if possible, for the first gallery, the foul-air pipes should descend. In the parquet and the orchestra, gratings arranged around the whole lower circumference of the partitions, together with other openings placed on top or on the sides of pipes carried along by the feet of the seats, will serve to direct the foul air in an interjoist placed under the floor. This interjoist, made high enough to be cleaned, should be divided in large theaters into two parts by a longitudinal divisiou in the mean plane of the edifice.

Each of these parts sbould communicate with a separato ventilatingchinney, of which the opening should be either in the basement or at the height of the floor of the passage-ways in the parquet.

In no case should the ventilating-openings be placed at the floorlevel, as has nevertheless been done at the Lyric Theater.

The foul air drawn off from the lower boxes and the first gallery should likewise be carried underneath by means of special pipes, afterward united in collecting-pipes terminating at the base of the chimneys just referred to.

The dimensions of these pipes should be determined on the condition that the velocity in them should be from 3 to 4 feet a second.

In small theaters, a single chimney will usually suffice for all the gal. leries. The calculation of the dimensions to be given to the foul-air openings should be made for each gallery separately, from the corresponding number of spectators.

The cast-iron smoke-pipes of the heaters should be carried into the ventilating-chimneys, keeping them separate throughout their whole height; and at the lower part of the chimney a grate should be placed, to be used whenever required, to increase the draught, especially in sum. mer. It would not be prudent, even in winter, to count upon the heat transmitted by the smoke-pipe to produce a sufficiently powerful draught.

The sectional area of the chimney should be calculated so that the mean velocity in it may be 54 or 6 feet a second.

They should open, when possible, in a cupola placed above the center of the hall, which should also receive all the ventilating-pipes of the upper stories.

A main ventilating-chimney should be constructed of brick and not of metal, above this cupola, the latter to be as low as possible, while the chimney should be made as high as the nature of the building will permit, but at least 20 or 25 feet.

The sectional area of this chimney should be calculated on the condition that the mean velocity of the draught in it should be about 64 feet a second.

127. Utilization of the heat given out by the lights. In addition to the pipes for carrying off foul air, the gases produced by the burners of tbe main chandelier or the other chandeliers suspended from the ceiling should also be carried into the cupola. The pipes intended to carry the gases there should be made as small as possible in order not to change the direction of the main draught in the vicinity of these places.

The diameter of the ventilating-pipe above a chandelier placed pear the ceiling and supplied with a metal or glass reflector should be calculated under the condition that it shall only remove 150 cubic feet of air an hour with the velocity of 13 feet a second to a cubic foot of gas consumed by the chandelier.

The single burners in the boxes and corridors should take the air necessary to support the combustion in the interior of the boxes or from the adjoining ventilating-pipes. It will suffice to make their ven. tilating pipes į or inch in diameter.

If, as is most probable, the plan of lighting through a glass ceiling, tried at the Théâtre du Cirque and the Lyric Theater, be not adopted, it will be advisable to place a circle of gas-jets at the base of the venti. lating-chimney, to be used only to increase the draught in summer, when the eleration of the temperature of the external air tends to reduce it. It may be assumed that under similar conditions each cubic foot of gas consumed will carry off about 800 cubic feet of air.

A valve should be placed at the foot of the chimney to moderate its draught, and particularly to stop the draught after the close of the play, to prevent useless loss of heat and the entrance of cold air during the night.

128. Ventilation of the stage. For theaters where great quantities of smoke are frequently produced during sham fights, grand illuminations, displays of fire-works, &c., it is well to keep up a strong draught in the upper part of the stage, in order to prevent the gases from being drawn into the auditorium by the draught kept up there, as happened at the Châtelet Theater, where these precautions were not taken. Further

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