488 IOWA DEPARTMENT OP AGRICULTURE 



this kind of wall than any other. It is also claimed that more freezing 

 occurs within the masonry silos than in the two-Inch wooden walls. Dry 

 wood is warm, but the wood next to the silage is never dry. No more 

 freezing occurs within a six-inch concrete silo wall than within a two- 

 inch wocden wall. Finally it is claimed that the acid formed in the 

 fei mentation of the silage destroys any masonry mateiial, steel or any 

 other substance aside from wood. The peculiar thing is that this same 

 acid is supposed to preserve wood. This acid is one of the weakest 

 organic acids and occurs in very low percentages. It probably has no 

 perceptive action on any materials either causing disintergration or pre- 

 venting decay. ... .„ j _ .J 



IMPORTANT ESSENTIALS. 



Before going into the details of construction we should understand the 

 requirements of a silo. Freshly cut green ccrn is simply packed tightly, 

 as nearly unilormly as possiole, in a large circular building, in the 

 absence of air there is a slight fermentation — a heating of the corn 

 up to a sufficient temperature to cook it considerably. The silage is to 

 corn what kraut is to cabbage. After filling the excessive weight of 

 this feed causes it to settle considerable. 



If the wall is not smooth there will be air-pockets between the silage 

 and the wall. This same pressure will cause the silage to press out 

 slightly tending to fill the small recesses in the wall, but the wall should 

 be as smooth as possible. Also the walls must be air-tight because any 

 air admitted to the silage will cause it to mould and decay. In order to 

 make the dcors tight they should be "mudded" in. Of course air comes 

 in contact with the silage at the top and enough corn rots to shut off 

 the air from the silage below. Careful tramping after settling will 

 reduce the loss, as less corn will be required for this air-tight cover. 



EEINFOECING MATERIALS. 



The settling of the feed, its heating, and consequently expansion, causes 

 considerable outward pressure on the silo walls. In order to prevent 

 the pressure from bursting the walls they should always be reinforced 

 with steel. 



Theie are a few cases of successful silos having been built practically 

 without steel. This, however, is no sign that it is safe as we simply 

 have no factor of safety and nobody knows how near these silos come to 

 bursting. There are many bursted masonry silos in the country. Though 

 a few silos without reinforcements have happened to stand, it is abso- 

 lutely unsafe to depend upon masonry alone to withstand this pressure; 

 steel must be used. This pressure amounts to about 11 pounds per square 

 foot for every fcot in depth; that is, at a depth of 40 feet the pressure 

 would be approximately 440 pounds per square foot. 



The cost of reinforcing does not exceed five to eight per cent of the 

 total cost of the building and it is the only way to make the building 

 safe. This pertains entirely to horizontal reinforcement, all hoops and 

 bands placed in the concrete. 



