DAIRY INSPECTION 135 



If the wind is very strong, air may also be forced out through 

 the inlets on the leeward side, but ordinarily the right-angled 

 bend in the inlets and the position of the outer opening at a 

 lower level than the inner prevents or retards the escape of 

 air through these inlets. In addition, wind passing over the 

 top of an outlet shaft produces a suction action within the flue, 

 and this draws air out of the stable. The force of this suction 

 action increases with the height of the outlet shaft, because 

 air movement or wind increases in velocity with the distance 

 about the ground. 



The heat given off by the animals in the stable through 

 the skin and in the respired air warms the stable air around them, 

 expanding it and decreasing its density or weight, which causes 

 it to rise toward the ceiling. Fresh air entering through the 

 inlets, being colder and heavier than the air in the stable, gravi- 

 tates toward the floor. Through the operation of these two 

 currents the stable air and fresh air are mixed, the fresh air 

 is warmed while the stable air is cooled and the moisture it 

 contains is diluted. However, when the respired air is cooled 

 below 81 F., it becomes heavier than fresh air of the same 

 temperature because of the carbon dioxide which it contains and 

 consequently settles toward the floor. For this reason, it is 

 desirable to have the outlet flues arranged to draw air from 

 the lower as well as the upper part of the stable. The expansion 

 of the air in the stable by the animal heat increases the pressure 

 within the stable and this has the effect of forcing air through 

 the outlets; the construction of the inlets prevents air from 

 being forced out through them. To obtain satisfactory results, 

 the air in the stable should be about 20 F. warmer than the air 

 outside. The effect of temperature differences on the draft in 

 outlet flues increases with the length of the flue. The resistance 

 encountered by air in passing through inlets and outlets modifies 

 to some extent the effects of wind and heat. It is therefore 

 desirable to have the outlet flues as straight as possible. 



Cloth Method of Ventilation. Stables may be ventilated by 

 covering windows with muslin or cheese cloth. Glass windows 

 should be alternated with the cloth-covered windows in order to 

 permit sufficient light to enter the stable. Three square feet 



