WARMING AND VENTILATION. 299 



not have any effect ou the stability of a well-constructed building with 

 a good foundation. 



On the contrary, if the ventilating-flues be carried ui^ward, the piers 

 of the third floor, which are only 10 feet by 2 feet=20 square feet in sec- 

 tional area, would be pierced by three flues, making a channel 3 x l'+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 ichere the icalls have notsufficient 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 j)revent 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 

 l^assage-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 excep- 

 tional cases, or in buildings already constructed presenting peculiar ob- 

 stacles, that the flues should be carried from below upward in the up]3er 

 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 veutilating-chimney, in order 

 to prevent as far as possible the establishment of communications from 

 one story to another. 



8G. Dimensions of ventilating flues and collecting -jyipes. — The sectional 

 area to be given to the first ventilating-passages should be calculated on 



OgQQ 



the basis of the renewal of 2,800 cubic feet of air an hour, or ^— = .78 



obOO 



cubic foot a second for each bed, and at a mean velocity of 2.3 feet a 



78 

 second, which would give ]j-^ = .31 square foot, or 49 square inches of 



