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sectional area for each bed; and as it is admitted that in common hospitals it will be sufficient to have one flue to every two beds, it will be necessary to have 98 square inches sectional area, or to make the flues, say, 9 inches deep by 11 inches broad.

For lying-in hospitals the volume of air to be renewed being 3,500 cubic feet an hour to each bed, or 98 cubic feet a second, the sectional area of the flues should be .43 square foot, or 62 square inches.

In the first collecting-pipes, which unite the flues by groups, a mean velocity of from 3 to 4 feet a second is allowed, and the sectional area may be calculated on this basis and according to the number of beds which it is necessary to ventilate.

The second collecting-pipes, if any are formed to receive the vitiated air from the preceding, should be proportioned by supposing a mean velocity of from 4 to 5 feet a second.

87. Ventilating-chimney.-Finally, in the main ventilating chimney, it is granted that the mean velocity should be about 6 feet a second, and that in the upper part it should be at least 63 feet a second, in order not to be checked by gales.

At the bottom of the chimney there should be an iron grate, surrounded by a brick rim, completely isolated from the walls, in order that the air coming in from the collecting-pipes may partly circulate around it, and only become warmed to a moderate though sufficiently high temperature.

In every case, there should be arranged a direct passage opening to the outside at the base of the chimney, through which the fireman may feed the fire.

If obliged to perform the work in the foul-air gallery, he would run the risk of being suffocated, or at least of experiencing much discomfort. The mean interior temperature of the chimney should in all cases exceed that of the external air by a constant difference of 36° to 45°, in order to give to the draught the same force at all times. The ventilat ing-fire should be much more energetic in summer than in winter.

Similar methods proportioned upon the same data should be adopted in cases where the arrangement of the different wards leads to the use of a single ventilating-chimney for a large number of buildings.

on.

Means for maintaining the regularity of the fire will be given further

SS. Cases where the foul air may be drawn off at the floor-level.-When the general plan adopted for the building includes a veranda on one side, the foul air may be drawn off at each story, to avoid the necessity of making vertical flues in the walls, by placing the ventilating-chimney at some point in the veranda, and carrying the ventilating-pipes into it, placing them between the floor-beams. (Fig. 29.)

A similar arrangement will render it easy to improve the ventilation by using a part of the heat from the kitchen and bath boilers, the hos pital-stoves, smoke-flues, kitchen-ranges, &c.

In such a case, each ward would have a main ventilating-chimney carrying off the foul air from each story in flues separated from each other as far as to the top of the upper story. At the bottom of each of the collecting-flues may be kept a little auxiliary heater, to be used only when neces sary in order to obtain a sufficiently powerful draught.

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of existing buildings.

It should also be understood that in every case the interior surface of the flues should be covered with as smooth a coating as possible, to diminish the resistance to the motion of the air, and that the openings should be arranged so as to permit of cleaning the flues at least twice a year, in order to remove the cob. webs and other obstacles which would interfere with the circulation of air.

In general, it would be well to place on top of the ventilating-chimney a cowl, which the wind would keep with its mouth away from the wind, so that strong winds would assist the draught, instead of checking it, as they would do without this precaution.

The proportions and the general arrangements which have been indicated should also be observed when it becomes necessary to draw off the foul air either at the level of the floors, as just mentioned, or at the top of the buildings, as will often occur, especially in the case

Whenever local conditions permit, the smoke-flues of the heating-apparatus should be carried up in the main ventilating-chimney, in order to use the heat they give out. They should be made of cast iron and kept separate.

89. Utilization of the waste heat of laundries and kitchens.-The furnaces of the laundry-boilers should, if possible, be placed at the base of the ventilating-chimney, in order to assist the ventilation by means of the heat given out in the furnaces by the gaseous products of combustion.

90. Application of the preceding rules.-Let us take the case of a hospital of 100 beds, containing two wards, with but one ventilating-chimney, hav. ing two stories, containing together 50 beds in each ward there being four halls with 12 beds, and two rooms with one bed each.

Under these conditions, each hall will contain six beds on each side,

and there will be three ventilating-flues, 100 square inches in sectional area, or 8x 12 inches.

The vertical flues should be carried under the floor of the groundstory, and joined to the first horizontal collectors intended to furnish passage to the air brought by the first, and each should carry off 12x.78= 9.36 cubic feet a second with a velocity of 3.28 a second. They should 9.36 then have a section of =2.86 square feet, or be 1 foot 8 inches 3.28

square, for example.

One of these flues, which would also ventilate the two single-bed bed. rooms, or 14 x.78=10.92 cubic feet, should have a sectional area of 10.92

3.28

=3.34 square feet, or should be 1 foot 8 inches by 2 feet.

If these pipes do not lead directly to the foot of the chimney, and if the general arrangements adopted render it necessary to carry the first collecting-pipes into a second collector, the volume of air which the latter will be obliged to pass will be 50×.78=39 cubic feet, with a velocity 39 of 4.6 feet a second. Its transverse section will then be equal to 8.50 square feet, and it may have the dimensions 2 feet 10 inches by 2 feet 10 inches.

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If the main ventilating-chimney should have to carry off the foul air of both wards, or that from 100 beds = 280,000 cubic feet an hour, or 78 cubic feet a second, with a mean velocity of 6 feet a second, its internal 78 sectional area should be- =13 square feet, and its mean internal diam6 eter 4 feet. At the upper part, this diameter should be reduced to 3 feet 10 inches to make the velocity there 63 feet a second.

91. Introduction of fresh air.-The openings for the introduction of warm or cold air should always be placed near the ceiling, and distributed as uniformly as possible throughout the whole extent of the halls in the proportion of one to every two beds if possible, or at least one to every four beds.

When they are made in the walls, they should be furnished with regis ters in the form of slats inclined 200 or 250 to the horizon in order to force the air in that direction toward the ceiling.

The transverse section of the vertical or other flues should be calculated so that the air will traverse them with a velocity not exceeding 3 or 4 feet a second. That of those through which the air flows immediately into the room should be determined by the condition that the entering velocity should not exceed 3 or 4 feet a second.

In the case where the air flows from above vertically downward, through openings in the ceiling itself, which may take place where double floors are used or where a loft serves as an air-chamber, the sum of the clear sectional area of the passages should be calculated on the condition that the velocity should not exceed 18 inches or 2 feet a second.

When ordinary heaters are used for heating, the warm air which they supply should be introduced before its admission into the halls into a mixing-chamber, where a sufficient quantity of external air is also admitted, in order to moderate as required the temperature of the air supplied to the rooms.

To secure the proper mixture of external air with the warm air from the heating-apparatus, it will be necessary to keep the fresh air above the current of warm air by means of more or less wide partitions. It will then happen that, as the first or denser stratum tends to fall while the second or lighter stratum rises, the mingling will necessarily take place. This applies as well to separate and direct openings for the admission of warm and fresh air in halls as to those for the admission of air into the mixing-chambers. The partitions should be made of brick laid flat, and be at least two inches thick.

During the period of fires, the temperature of the inflowing air should, for healthful ventilation, differ as little as possible from that intended to be kept up in the halls, which should be uniformly about 60°.

The mixing-chambers should be formed either in the floor above the the heaters or in the corridors or small rooms.

Registers should be placed in the mixing-chambers, to permit the temperature of the air supplied by them to be regulated at will.

Similar arrangements should be made when hot-water or steam heating-apparatus is used.

If the hospital stands by itself and is in a healthful location, the external-air supply may be taken either at the ground-level from the middle of a lawn or flower-bed, as at Vincennes and the lying-in hospital at St. Petersburg, or at the level of each floor.

Descending currents will not be required to carry the air from a certain height, except in cases where the proximity of more or less unhealthful buildings would lead to the fear of infection in the air at the ground-level.

In that case, the chimney for bringing in air should be placed as far as possible from that for carrying it off. The sectional area of the former, and in general that of all external openings for the admission of air, should be calculated so that the velocity of admission should not exceed 2 feet a second, in order that the draught produced in the vicinity of the openings may only extend a small distance.

The openings for the admission of air entering at a considerable height should be provided with valves or doors, which may close them if required.

In summer, when the action of the draught in drawing in fresh air is not assisted by the increase of temperature which the heating-apparatus gives to the fresh air in winter, there should be made in the walls, especially on the faces exposed to the north or the east, auxiliary openings similar to those previously mentioned, and capable of being opened or

closed at will by means of internal valves furnished with self-closing springs.

As the air thus introduced may be too cool at night, it is necessary that it should be directed from the lower part of the room toward the ceiling, and that its velocity at entrance should be about 2 feet a second, in order that it may be rapidly diminished before it arrives at the escape-openings.

The regulating-apparatus connected with the registers should be so arranged as to be exclusively under the control of those in charge of this service.

When any arrangement for ventilation on the exhaust-system has been carried out, it may easily be determined by direct experiments easily made in the main ventilating chimney, or, if desired, in the separate flues, whether the prescribed amount of air is really drawn off, and what is the corresponding excess of temperature in the chimney over that of the external air; and if with this excess, which usually will not vary, as has been previously stated, much from 350 to 45°, the ventilation be found sufficient, it will then only be necessary to regulate the heat in the chimney so that its temperature will always exceed by the same amount that of the external air.

92. Arrangements for ventilation in summer.-When the main halls of the hospital are warmed at the same time by general heaters and by fire-places-of which latter the ventilating fire-places described in § 13 should be preferred, as they at the same time carry off foul air and introduce a considerable amount of fresh air properly warmed-openings for the admission of fresh air should be made in addition to those of the ventilating-chimney, and arranged, as has been described, for

summer-ventilation.

Stairways, waiting-rooms, and other places giving access to the halls should be heated to a temperature which, especially for the latter, should be at least equal to that of the halls. In this way, their effect in producing draughts of air will be diminished. It would be well, then, to put up heaters in these places even when fire-places are used in the main rooms.

93. Use of the heat given out by the lights.-In hospitals lighted by gas, it will be well to assist the draught by means of the heat given out by the burners, which plan will have the double advantage of rendering the ventilation more energetic, and of removing the unhealthful products of combustion. This should especially be applied in the case of waterclosets, which should have double doors opening from without inward in the direction of the draught.

The kitchens and the privies of hospitals should be removed from the hospital proper, and ventilated by a powerful current similar to those which will be described hereafter for such places.

94. Dispositions to be made in case of crowding or epidemics.-When the draught is produced by a circulation of warm water or steam, the energy

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