SILAGE PRESERVATION 21 



silo. The cold air falls, thus the circulation continues to 

 carry away heat from the silage. If the circulation of air 

 is restricted by horizontal partitions, this circulation and 

 consequent loss of heat does not occur. 



In double-wall wood silos, it is often well to provide for 

 circulation at times. After the silo is emptied, air can be 

 allowed to circulate in the walls, thus drying them and pre- 

 venting rapid decay, which would otherwise occur. This, 

 however, is not the case with masonry silos. There seems to 

 be no advantage of air circulation in the walls of masonry 

 silos, and there certainly are very marked disadvantages. 



Influence of Materials. Materials differ in the ease 

 with which heat passes through them; or, as it is generally 

 stated, there is a difference in their conductivity. Aside 

 from this, about the only general law of heat transfer which 

 need be considered is that, other things being equal, the rate 

 of heat flow through the wall will vary inversely as the 

 thickness of the wall or the distance which the heat must 

 travel. Heat will pass through a 1-inch wall twice as rap- 

 idly as through a 2-inch wall of the same kind. Also, the 

 content of moisture increases the conductivity of most 

 materials, because the pores of the material contain moisture 

 instead of air, and air is a poor or slow conductor of heat. 

 Thus it will be seen that while dry wood is a very poor 

 conductor, wet wood conducts heat very much more rapidly. 



Although there are several other features in silo building 

 more important, it seemed advisable to explain this 

 matter of freezing in order to correct the misunderstanding 

 that a 2-inch stave silo is so much warmer, or is so much less 

 subject to freezing, than a thicker masonry wall. The actual 

 facts do not bear out any such impression as this. In fact, 

 about the only way to secure marked improvement in this 

 respect is to build two walls entirely separate and if possible 



