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pounds of damp linen, in which 35 pounds of water remain after they have been wrung.

The evaporation of these 35 pounds of water is effected in an hour by the consumption of about 11 pounds of coal.

The temperature of the chamber is kept at 158°, and the amount of air passing into the chamber varies from 35,000 to 42,000 cubic feet an hour.

Four chambers, with their 32 rods, are attended to by one woman, who fills and empties them.

According to the rules previously given, the 35 pounds of water evaporated, requiring 35 × 117040950 units of heat, and the 11 pounds of coal giving 159,000, the calorific effect of the apparatus is 40950 = .26. 159000

equal to

The same result was also obtained from some experiments made for seven years at La Saltpetrière, in which, with a consumption of 6,415 pounds of coal, 18,940 pounds of water were evaporated, the calorific effect in these experiments was found to be .24.

POWDER-DRYING ROOMS.

79. In the case of powdered materials spread out to a certain thickness, it is often necessary to use blowers which drive the air under a table, closed on all sides, the top of which is formed of wire-gauze, on which the substances to be dried are placed.

6

Thus, in powder-mills, the air driven under the gauze has ordinarily a pressure measured by a column of water 3 or 4 inch high, and a temperature of 1120 to 140°. The thickness of the layer of powder varies from 1 to 3 inches, according to its nature. The air is heated to the proper temperature by means of water or steam pipes.

Although, in such cases, blowers are most frequently used, the same result may often be obtained by means of a well-regulated draught alone. At the powder-mill of St. Chamas, a drying-room, warmed by hot-water pipes placed under the table, and supplied with a chimney containing a hot-water vessel to produce a draught, has worked satisfactorily even in the case of blasting-powder containing 8 or 9 per cent. of water.

BARRACKS.

80. The volume of air to be renewed every hour for each individual being given at 1,000 cubic feet during the day, and 1,400 to 1,800 during the night, the proportions and arrangements of the openings will be determined by the preceding rules.

But it is principally, and it may be said solely, during the night that the ventilation of the barrack-rooms is necessary, since, during the day, the soldiers are almost always out of it.

The heating of these rooms during the day is intended only to enable

those who return from duty, after getting wet, to dry their clothes and shoes; for this purpose, ventilating fire-places are preferable to sheet-iron stoves, because, in addition to the radiant heat they give out, they have in this case the advantage of carrying off the vapor arising from the damp clothing, which would make the room unhealthy and disagreeable. The fire never needs to be kept up long, and it cannot be counted upon to produce a constant change of air.

If natural ventilation alone be employed, it is necessary, according to observations made at the Bonaparte barracks in Paris, that the openings for the admission and discharge should be proportioned as follows: Area of openings and flues to each bed in summer: discharge, 31 square inches; admission, 62 square inches.

In winter, spring, and autumn, these proportions would be excessive, and means should be provided for closing part of the openings, so as to confine the circulation of air within proper limits. But the regulation of the registers or valves should not be left to the discretion of the soldiers.

The necessity of preventing the soldiers, in their ignorance, from stopping up the escape-openings requires that in this case the rule should be violated which prescribes that these should be placed near the beds and the floor, as it will be necessary to place them near the ceiling, as well as those for the admission of fresh air.

The first should open above the space between the beds, and the flues should be placed near the smoke-flue or should receive the stove-pipe when stoves are used. The second, intended for the introduction of fresh air, are also placed near the ceiling, and made in the face of the opposite wall.

This arrangement presents the advantage that if, as often happens in ventilation due simply to the action of natural temperatures, the direc tion of motion changes so that the escape-pipe becomes that of admis sion, no discomfort is experienced by the men, who in both cases are removed as far as possible from the openings.

These precautions will be completed by placing horizontal or inclined shelves under the openings, which will force the air always to remain nearly or quite horizontal in entering or passing out.

There is no reason to fear that the air flowing in will immediately rush to the escape-openings before circulating through the rooms; the difference of internal and external temperature will always enable the circulation to be maintained.

81. Utilization of the lost heat of cooking-stores.-In most barracks, the cooking-arrangements of the companies which occupy that part of the building reached by one staircase, and often also all those used for a whole wing, are collected in a single room on the ground-floor, devoted to this purpose. There, separate stoves are used, in cooking, for each company, squadron, or battery. Beside these stoves, strongly heated twice a day, or even in their chimneys, it would be very easy and inex

pensive to place hot-water receivers in the form of a drum, or of pipes such as are often used in heaters, into which hot-water pipes should be tapped, and then carried vertically in the foul-air flue leading from the rooms, thus securing a change of air at all times and without expense. In this way, also, baths might be supplied, which would be of great service for soldiers' hospitals. Ventilation being, as has been said, much more important at night, when all the men of one mess are together, than during the day, when most of them are out of doors, the registers -the regulation of which should only be made by the order and under the direction of the adjutant of the week-will serve to check or prevent escape of air during the day, so as to accumulate heat in the flues for the night.

HOSPITALS.

82. General plans and dimensions to be adopted for the ventilation of hospitals. It is only proposed in what follows to give the proportions of the principal parts of the flues and pipes which it is necessary to use for the ventilation of hospital-wards, in order to secure the removal of vitiated air and the introduction of fresh air.

These proportions apply also to the different plans which local conditions may cause the architect to adopt.

The amount of air to be renewed in the sick-rooms may vary, according to circumstances, from 2,000 to more than 3,500 cubic feet an hour for each bed; 2,800 will here be taken as a basis for the calculations.

When local conditions permit, the foul air should be drawn off through descending passages; openings into them being made behind the head of the beds, at the floor-level, but in the vertical walls, to be in number at least equal to one for every two beds in ordinary hospitals, and one to each bed in lying-in hospitals.

When a hot-water heating-apparatus is used, and when the plans adopted as well as the proximity of chimneys permit, the waste heat from the small heaters and hot-water tanks used in the hospital should be made use of to assist the draught.

But it is not necessary that the use of these little reservoirs, which have but a small capacity, should lead to the exclusive adoption of the up-cast draught, as L. Duvoir has done, and which is less advantageous. 83. Advantages of the down-cast draught.—It will be remembered that the arrangements required by the down-cast draught lessen very much the weakening of the walls by the passage of ventilating-flues.

Thus, for a building with rooms on three floors, as in the case of Lariboisière Hospital, the piers of the third story are not pierced for any flue, because their own commences at the floor; those of the second story are only pierced by a single flue coming from the third floor; and those of the ground-floor only contain the two flues belonging to the second and third stories.

The thickness of the walls being greater at the lower stories, the flues would always be proportionally less injurious with descending draughts

than with ascending draughts, the latter requiring the largest number of flues to be made in the upper stories, where the walls are thinnest. Figs. 27, 28, which represent only the general features, show the ad

FIG. 27

FIG.28

vantages presented by down-cast draughts over up-cast draughts as regards the weakening of the walls by the ventilating-flues. The downdraught, besides, as we have said, renders it easy, in order to give due force to the draught, to make use of the entire height of the main ventilating-chimney, to the bottom of which the flues are connected. It forms a very economical means of utilizing the heat expended in producing it. For a building of a construction similar to that of Lariboisière Hospital, where the piers at the ground-floor have a mean width of 10 feet and a thickness of 2 feet 7 inches, or 26 square feet of sectional area, the two flues are carried from the second and third stories to the basement, they require, at most, in the walls-including the partition between them and even the interior brick lining-a space 2x1'+1"-2' 1" broad, and 9"+2"-11" deep, or a total sectional area of 1.9 square feet; that is to say, one-fourteenth of the total sectional area of the pier, which could

not have any effect on the stability of a well-constructed building with a good foundation.

On the contrary, if the ventilating flues be carried upward, the piers of the third floor, which are only 10 feet by 2 feet=20 square feet in sectional area, would be pierced by three flues, making a channel 3× 1'+3′′ =3′ 3′′ broad, by 11" deep, or 2′ 9" sectional area, equal to one-seventh that of the masonry. This would not be admissible.

In cases where the flues for the introduction of fresh air have also to be provided for in the piers, though this can sometimes be avoided in hospitals the wards of which contain only twelve or fourteen beds, it will be seen, then, that the enfeebling of the walls by the passage of all the flues will not endanger the solidity of properly-built walls.

84. Cases where the walls have not sufficient thickness.-When the nature of the materials used or local circumstances do not permit of giving the walls sufficient thickness to allow of cutting flues in them with safety, ventilating-shafts may be made projecting from the walls in the interior of the rooms, making them of light brick work. Then, to diminish as little as possible the available breadth of these rooms, and to prevent hurting their appearance, the depth of these flues should be restricted. by making them occupy almost the entire breadth of the piers.

85. Arrangement of the ventilating shafts.—The necessary arrangements should be made to prevent ventilating shafts or flues from being crossed by the beams or joists of the floor, which can easily be avoided by the use of trimmers.

If there are no cellars under the buildings, which is not indispensable, sufficiently large vaults should be made to give the necessary area of passage-ways, and these should be covered on top, as well as the floor of the first story, with a coating of tar-concrete, to protect it from moisture. If any difficulty be encountered in carrying the ventilating-flues below the floor of the first story, they may stop at this floor. It is only in exceptional cases, or in buildings already constructed presenting peculiar obstacles, that the flues should be carried from below upward in the upper floors or in the roof.

In every case, the discharge-flues corresponding to beds placed on dif ferent floors one above another, should be kept separate in their verti cal course and not united in groups in partial horizontal conductors, unless separated by partitions for an extent of 10 or 12 feet beyond the outlet of those which are the nearest to the main ventilating-chimney, in order to prevent as far as possible the establishment of communications from one story to another.

2800
3600

= .78

86. Dimensions of ventilating flues and collecting pipes.-The sectional area to be given to the first ventilating-passages should be calculated on the basis of the renewal of 2,800 cubic feet of air an hour, or cubic foot a second for each bed, and at a mean velocity of 2.3 feet a .78 second, which would give.

=.34 square foot, or 49 square inches of

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