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Rh days, but in the case of concert halls, theatres and similar buildings, it is possible (and most essential) thoroughly to aerate the building between each occupation.

The extraction of foul air should in most cases be effected at the top of a room or building, so as to utilize the natural tendency of warm air to' rise; but at Birmingham and elsewhere the Sjgzj' outlets are near the floor, the fresh air being brought in "dated half-way up the walls and directed towards the ceiling. 3” The air inlets should be Tobin tubes or similar devices, placed some 4 or 5 ft. above the iioor, and so arranged that the air should be passed in contact with radiators or pipes to warm it before entering. In the case of a building for one of the American legislatures, the warmed fresh air is allowed to enter on the level in front of the desk of each member, so that he secures a proper volume of fresh air for his own use before it is breathed by his neighbour. The introduction of rapidly revolving, but silent, fans, driven by electricity, is a great advance whlgch places Fvithir; the riach olglthe en ineer or arc itect the means or so vin the ro em Fans' of ii/epitilatiog of buildings, hand has been foga larglgrixtzent res onsible for the rapi progress o the art o Venti ation. e an and) motor combined extend the advantages of positive mechanical ventilation to all who have access to electric current, with the further benefit that the extreme simplicity of the electric driving of the fans greatly facilitates the control and distribution of ventilating effect. The moderate power required by these fans for a given duty has contributed greatly to their extended use. They should deliver into a chamber of considerable size, so that the velocity of the air may become reduced before it passes into the distributing Hues. The question of silence in running, in such places as houses of parliament, law courts, churches and chapels, is of paramount importance, and no fan should be accepted until it is proved by actual working to be noiseless.

In some instances revolving pumps of the Root's blower type are used (see BELLOWS AND BLow1NG MACHINES). At the Dundee College a battery of five of these blowers, each discharging over 150,000 cub. ft. of air per hour, is driven easily by a gas engine of two horse-power. The air is passed through two filters of coarsely woven fabrics which serve to remove all particles of impurity. The rooms are heated by having coils of Perkins's high-pressure hotwater pipes (see HEATING) in the main distributing flues. The inlets are flat upright tubes extending ug the side walls to a height of nearly 6 ft., and open at the top. utlets are generally provided in the end walls, one group near the ceiling, another a few feet from the foot. They are fitted with doors which allow one or other to be closed; the high-level outlets are used in warm weather, when the fresh air that comes in is com aratively cool; the low-level ones are used in cold weather, when the fresh air, having been heated before it enters, would tend to rise and pass out too directly if the outlets near the ceiling were open. The outlet shafts communicate with a louvred tower or turrets on the roof. Each room receives a volume of air equal to its cubic capacity in about 12 minutes, so that the atmosphere is completely changed five times in an hour. The inlets are proportioned to do this wit out allowing the velocity with which air enters to exceed 6 ft. per second.

The water-spray ventilator is a mechanical ventilator using a. jet of water to impel the air. A nozzle at the top of a circular Wafer' air-shaft delivers a conical sheet of water, which impinges ZZ-;; on the sides of th.e shaft a little way below and carries star down with it a considerable stream of air. This ventilator is used either to force air into rooms or to draw it out; in the former case a small stove is often added to heat the supply. In the early days of mechanical ventilation extraction by a hot-air a more common mode of ventilating hospitals and other public buildings than now. The heat was applied by a shaft was

gffxc' furnace or stove at the bottom of the shaft, or by coils hot a;' of hot-water or steam pipes. In the lecture theatre of the sham Paris Conservatoire des Arts A. ]. Morin employed this means of extraction, and arranged that the fresh air should enter through the ceiling and the foul air be drawn off through the Hoor from under the seats; this reversal of the natural direction of the current is of course only possible when a sufficient external motive force is applied.

In theatres and similar buildings clusters of gas jets or sunlight burners, fixed at the ceiling level at the base of a metal shaft which is connected with the open air, serve as effective ventilating agents Eyuextracting the foul air which collects in the upper part of the a

To ensure the admission of the desired amount of air into a !'O0m, and to arrive at the proper allowance of inlets and outlets, it is The necessary /to ascertain the direction and velocity of the measurh movement of the air through the m. The quantity ofair ment passing through a given opening is found by multiplying “fam the area of the opening expressed in square feet by the velocity of the current of air stated in lineal feet per minute, the product being the number of cubic feet passing per minute. Where the air is admitted through gratings only the clear area should be calculated, the amount of solid material being deducted from the gross superficies of the grating. The velocit of the air current may e determined by means of an anemometer fg.v.).

We may conclude with a short summary of the methods adopted of ventilating a. number of typical buildings of various classes of different countries.

The Smallpox Hospital at Bradford consists of two wards, 75 ft. by I5 ft., placed back to back, with a space of about 3 ft. between them enclosed by walls forming a foul-air chamber of the same length as the wards, and reaching to the ceiling. At this level are outlets for the vitiated air-one over each bed. A furnace at the base of a tall shaft withdraws through these outlets the air which passes through the furnace on its way to the outer air. The windows are tightly closed and fresh air enters from a chamber below through gratings in the floor at the foot of each bed.

The New York General Hospital was stated in 1875 to contain 163 beds. In the wards there is one window to each bed, each pier between the windows containing a foul-air extracting flue running from the base of the building and connected in the roof with large trunks leading to an exhaust fan. The heating is by steam coils placed in the basement in such a way that by a valve the cool fresh air can be sent either through or around the heating coil. The warmed fresh air is conveyed through an air-tight iron pipe fitted in each extracting shaft and is admitted to the wards through slits in the window-sills forming a jet directed upward on the principle of Tobin tubes. The outlet openings for the foul air are placed one beneath each bed, with extra outlets for occasional use at the top and base of the external walls. The placing of the freshair supply pipes in an inaccessible position inside the foul air ducts cannot be approved for hospital ventilation, as it is quite possible that in time, through the decay of the pi e joints or of the pipes themselves, communication may be established between the fresh and foul air, thus entirely upsetting the system of ventilation. The City Hospital of Hamburg, containing 130 beds, was opened in 1890. The buildings are one storey high and are heated on the ancient Roman hypocaust principle. Beneath the entire floor run longitudinally a number of brick and concrete Hues about 30 in. square, covered on the top with marble tiles, forming the floor of the wards. In these flues are placed the steam heating pipes. Warmed fresh air is admitted through large radiators in the centre of the wards, the vitiated air escaping through o enings in the ridge of the roof. Mr H. Percy Adams adopted a similar by ocaust method for warming the chapel and the dining-hall at the }I){i g Edward VII. Tuberculosis Sanatorium at Midhurst, Sussex, except that -the radiators are omitted from the centre of the rooms, and placed in recesses in the side walls.

In the Houses of Parliament at Westmiilstery which were designed and built for the public business in 1836, considerable attention is devoted to the question of the purification of the air, but the arrangements are lamentably antiquated and ineffectual in their working. The supply of fresh air is drawn by fans from the terrace at 'the river front, and, after being warmed and moistened or cooled by water-spray or blocks of ice, as the temperature may require, passes through exceedingly tortuous and restricted air passages to the various chambers, where it is admitted through large gratings in the floor, which are covered by porous matting to prevent draughts. The outlets for the vitiated air are in the ceilings of the apartments, and from these the air has to be dragged down to the base of the ventilating shaft in the Victoria tower, where an up-current is maintained by a large furnace.

The French Chamber of Deputies, according to a report made by M. Frélat in 1891, is much overcrowded, the allowance of floor space for each member being only 30 square centimetres. The apparatus is powerful enough to change the air every six minutes, but to avoid draughts it can only be worked slowly. Fresh air is driven down by a fan through openings in the ceiling, and vitiated air removed at the floor, giving a downward system of ventilation. For the ventilation of the new Sessions House at the corner of Newgate Street and Old Bailey, London, opened in 1907, an elaborate system on the plenum downward principle was installed The fresh air, drawn in at the basement by powerful fans, passed in turn through purifying screens, on which water was constantly playing, and over steam-heated coils, before entering the distributing trunks; into these sufficient cold air also was admitted to reduce it to the required temperature. Branch ducts conveyed this warmed fresh air to the points of inlet just below the ceiling. The outlets for the vitiated air were placed near the floor level, an electric fan drawing it up and discharging it at the roof. It was claimed that 600 tons of filtered and warmed or cooled fresh air were passed through the building every hour.

In the Capitol at Washington in .America the upward system is installed. Fresh air, warmed by coils in the basement, is delivered by means of fans through openings in the floors of the various chambers and galleries, and the extractors are placed in the ceilings. This foul air passes out of the building through louvre ventilators placed on the roof ridge. Some of the vitiated atmosphere, however-that from the corridors and galleries-is drawn by means of a fan to the basement and blown up a lofty shaft. The Grand Opera House in Vienna is ventilated on a most elaborate and complete system, the arrangements there giving excellent results. The scheme for heating and ventilating this