Buildings and Yards. 545 



The warm vapor and the expelled air being warmer, rise at once to 

 the top of the room. If an opening is made in or near the ceiling, the 

 vitiated air and the vapor will escape. Assuming a still atmosphere on 

 the outside, the rapidity will depend, among other things, on the size 

 of the opening, the readiness with which other air can enter to take its 

 place, and the difference in temperatures between the inside air and the 

 outside air. The greater the rapidity with which the exchange of air takes 

 place, the drier and purer the air will be ; but when colder outside, the 

 greater the exchange of air the colder the room will become. 



Since in barns without artificial heat the only method of warming 

 the room is from the heat of the animal bodies, it becomes a matter of 

 balance between too much moisture and bad air on the one hand and 

 too much cold on the other. The heat will be retained the longest 

 and hence the temperature maintained the best by taking in the cold 

 air near the top and taking out the less warm air near the bottom. 

 This gives the cold air opportunity to become mixed with the warm- 

 est air and takes out the warmer after it has given up the largest 

 practical amount of heat to the incoming cold air. This, however, is 

 the least effective method so far as obtaining pure dry air is concerned. 

 Indeed, frequently with this method, especially when the opening for the 

 entrance and escape of air is inadequate, serious difficulty on account of 

 dampness is encountered. If the driest and purest air is desired, allow 

 the warm air and vapor to escape at the ceiling. The best method of 

 securing fresh air in any case is to allow it to enter at the sides above 

 the heads of the animals in such a way as not to cause draft on the animals 

 and in order that it may absorb as much heat as practicable from the 

 warmer air before descending into the room. 



There remains one factor in ventilation yet to be mentioned. The wind 

 is in many respects the most important factor in determining the purity 

 of the air of a building or, in many cases, of a whole city or state. In 

 the heating and ventilation of public buildings, it is not uncommon to 

 force a given amount of tempered air per second or hour into the room, 

 in which case a similar amount must escape ; or, in other cases, a given 

 amount of air is exhausted from the room, when an equal amount must 

 enter. It is much like putting a rope through a knot hole. It may be 

 pushed through or it may be pulled through. The result is the same. 

 The point to note is that this exchange of air takes place without any 

 reference to the relative temperature or density of the air. It takes 

 place because it is forced to do so. 



A wind passing through an opening two feet square at the rate of 

 ten miles an hour will fill a stable 30x50x10 feet with fresh air in less 



