THIRTY-SIXTH ANNUAL CONVENTION. 309 



Imperviousness of the Walls. 



Hard burned hollow clay building blocks will not absorb a 

 large amount of water. Moisture is not readily transferred 

 through a wall of such material. We recommend that only 

 blocks which have a low absorption be used for silo construction. 

 Blocks of this kind are more durable, and a silo built of them 

 will preserve silage better. 



The mortar used in laying the blocks should be a rich, water- 

 tight mixture. This will resist the passage of moisture or air 

 through the joints. To secure a more perfect wall, it is recom- 

 mended that the inside be washed with cement. This will seal 

 any minute openings or imperfections. 



A careful personal inspection has been made of the silage in 

 the thirteen Iowa silos which have been built up to the time of 

 writing and, with one unimportant exception, the silage was 

 found in first-class condition throughout the entire feeding 

 season. There is no reason why the walls of the Iowa silo 

 should not be entirely satisfactory for the preservation of silage. 

 That they are satisfactory has been demonstrated by actual test.. 



Rigidity, Strength and Smoothness of Walls. 



The outward or bursting pressure of silage has been found 

 by previous experiment to amount to about 1 1 pounds per cubic 

 foot. To be well designed, any silo must be constructed of ma- 

 terial of sufficient strength to resist this pressure. Square silos 

 are not well adapted to resist this bursting pressure on account of 

 their flat sides. They are almost sure to bulge. For this reason 

 the round silo is the most desirable form. 



The silo, owing to its diameter and height, offers a rather 

 large amount of surface upon which the force of the wind may 

 act. For this reason the silo walls should be of rigid construction 

 and not readily distorted or damaged by high winds. Further- 

 more, it is best that the structure should be heavy enough when 

 empty to resist being moved readily from its foundation by strong 

 winds. Some types are so light that they must be thoroughly 



