470 



AGRICULTURAL ENGINEERING 



blocks are of the same material and have the same character- 

 istics as brick; in fact, in certain localities they are called 



hollow brick. If these 

 blocks are of good mate- 

 rial and hard-burned they 

 are very durable. 



The 4x8xl2-inch block 

 has proven to be a very 

 satisfactory size. Larger 

 blocks are too large to 

 handle with one hand, and 

 smaller ones require more 

 labor in laying. These 

 blocks are laid on edge, 

 making a four-inch wall. 

 The Cement Wash. If 

 curved blocks are used 

 and care is used in point- 

 ing and filling the mortar 

 joints, the wall will be suf- 



Fig. 296. The Iowa silo made of hollow ficiently SHlOOth On the m- 



side to omit the plastering. 



To seal the mortar joints and make the whole impervious, 

 a cement wash should be applied before the mortar becomes 

 hardened. 



Reinforcement. The . entire bursting pressure of the 

 silage should be carried by steel wire imbedded in the mortar 

 joints. Number 3 wire has been found to be a very satis- 

 factory size. It is small enough not to interfere with the 

 laying of the blocks, and fewer strands are required than of 

 the smaller sizes. This wire should be unannealed, and may 

 be straightened to the curvature of the silo by drawing it 

 through a piece of pipe bent to the proper angle. 



