128 



CITY MILK SUPPLY 



breathed, it is advantageous to renew it frequently, and that, the location 

 of the mouths of the outlets near the floor accomplishes. Near the 

 ceiling the outlets are provided with registers or intakes that are kept 

 closed in cool weather but in hot are opened for the double purpose of 

 cooling the barn and increasing the draft. 



In small barns a single large outlet flue is best; large barns require 

 several of suitable size. King has stated that a ventilating flue 2 by 2 ft. 

 through which air moves at 295 ft. per minute gives sufficient air for 

 20 dairy cows. However, he points out that it is the temperature in the 

 outlet flue that largely determines the draft and that the motive power 

 for ventilation due to temperature, increases with the height so that this 

 factor should be taken into account in practice and he holds that out- 

 takes and intakes for cow barns should provide for not less than 30 sq. 

 in. per head, when the out-take has a height of 30 ft. ; if the out-take is 

 shorter the area should be greater, if higher it may be less. A 20-ft. out- 

 take should require about 36 sq. in. per head instead of 30. 



Canadian Experiments. Grisdale and Archibald of the Dominion 

 Experimental Farms at Ottawa have made an interesting study of the 



t 



IT 



KING SYSTEM 



Masonry 



Stone Wall 

 Air Space and Wooden 



Lining 



Building Papers 

 ir Sr>;ire 



RUTHERFORD SYSTEM 



FIG. 26.' 



The King and the Rutherford systems of ventilation. (From Bui. 72, 

 Dominion Experimental Farms.) 



