VENTILATION AND LIGHTING 



231 



In any successfully ventilated building advantage is taken of the fact that 

 warm air ascends. A small shaft may be fixed over the head of each 

 horse; but in practice it is found that one large shaft, about a foot 

 square, will purify a stable containing four or five horses. It is better 

 to fix this about the middle of the stable, as regards its length, but 

 near the heads of the horses, or else as shown below in the section of 

 a stalled stable. The tube should be made of zinc. Wood is not good, 

 as in the course of time, by shrinkage or accident, the joints are apt to 

 open, and then the action is spoilt, but when the zinc tube j)asses through a 

 fodder loft or room, it should be cased in wood for protection. 



The upper end of this shaft should be guarded from down-draughts, either 

 by a cowl which will turn with the wind, or by a covered ventilator of galvan- 

 ized iron fixed on the ridge of the roof, the price of which will depend on 

 the size. At the bottom a sheet of zinc, or a board, considerably larger 



than the shaft, should be fixed about 4 in. below the mouth, so as to 

 prevent any down-draught striking the horses, and also to catch any drip 

 from the condensation of the steam of the stable, as it comes in contact with 

 the interior of the shaft. The bottom of the tube should be fitted with a 

 flap for regulation. Loose boxes must be ventilated separately, if they are 

 not open to the stable; but if they are, the same shaft will take off their 

 foul air as is used for the stalls, provided there are not more than four 

 or five horses in the same space. A shaft about 6 in. in diameter is 

 amply large enough for one box; and this, with the ventilating window or 

 the separate ventilator I have described, will keep any box in a healthy 

 condition, if its drainage is properly attended to. There is a veiy common 

 notion that no ascending shaft will remove the carbonic-acid gas, which is 

 one of the results of respiration, because its specific gravity is so great that 

 it lies close to the floor. This, however, is a fallacy in practice, though 

 perfectly correct in theory, because all gases have a tendency to mix rapidly 



