SIZE OF THE SILO. 23 



the mass from settling uniformly, and air spaces in the mass thus 

 formed will cause the surrounding silage to spoil. 



4. The walls of the silo must be rigid and very strong so as 

 not to spring- when the siloed fodder settles. The lateral (out- 

 ward) pressure of cut fodder corn when settling at the time of 

 filling is considerable, and increases with the depth of the silage 

 at the rate of about eleven pounds per square foot for each foot of 

 depth. At a depth of 20 feet there is, therefore, an outward pres- 

 sure of 220 pounds; at 30 feet, 330 pounds, etc. In case of a 16- 

 foot square silo where the sill is 30 feet below the top of the silage 

 the side pressure on the lower foot of the wall would be about 

 16x330, or 5,280 pounds. 



It is because of this great pressure that it is so difficult to 

 make large rectangular silos deep enough to be economical, and 

 it is because the walls of rectangular silos always spring more or 

 less under the pressure of the silage that this seldom keeps as 

 well in them as it does in those whose walls cannot spring. 



As the silage in the lower part of the silo continues to settle, 

 the stronger outward pressure there spreads the walls more than 

 higher up and the result is the wall may be actually forced away 

 from the silage so that air may enter from above; and even if 

 this does not occur the pressure against the sides will be so 

 much lessened above by the greater spreading below that if the 

 walls are at all open, air will more readily enter through them. 



In the round wooden silos every board acts as a hoop and as 

 the wood stretches but little lengthwise there can be but little 

 spreading of such walls, and in the case of stave silos the iron 

 hoops prevent any spreading, and it is on account of these facts 

 that the round silo is rapidly replacing every other form. 



After the silage has once settled, there is no lateral pressure 

 in the silo; cases are on record where a filled silo has burned down 

 to the ground with the silage remaining practically intact as a 

 tall stack. 



Other points of importance in silo building which do not apply 

 to all kinds of silos, will be considered when we come to describe 

 different kinds of silo structures. Several questions present them- 

 selves at this point for consideration, viz., how large a silo shall 

 be built, where it is to be located, and what form of silo is pre- 

 ferable under different conditions? 



