298 SOILING CROPS AND THE SILO. 



above the surface of the ground. Flat stones are 

 preferable to round ones, but round stones will 

 answer. The wall may be flat on top, but many 

 favor making a shoulder on the outside as shown in 

 figure 30. The staves of the silo should stand inside 

 the shoulder and close against it. If, when the 

 hoops are drawn tightly, the staves should be drawn 

 away from the shoulder, the space should be filled 

 by pouring thin cement into it. 



When building the foundation wall, some 

 authorities recommend digging a trench of the de- 

 sired depth and filling it with stones, putting the 

 largest stones in the bottom. Smaller stones are 

 worked into the intervening spaces, or they are filled 

 with gravel. In either case they are pounded down 

 until quite firm. When the wall is finished, a thin 

 cement is made and poured over the wall so 

 as to go down in the interstices. When it has 

 set, stronger cement is spread over the surface 

 with a trowel. It is questionable, however, if 

 cement thus applied has any advantage in cheap- 

 ness or otherwise over the good old-fashioned 

 mortar for holding in place the stones of a foun- 

 dation wall. 



When a shoulder is not used on the wall the 

 time for striking a circle to serve as a guide in set- 

 ting up the staves is opportune, while the cement or 

 mortar on top of the foundation wall is still soft. 

 In making it a stake may be driven into the center 

 of the floor of the silo. The circle on the wall is 

 then marked by some suitable implement attached 

 to a cord which moves around on the central pivot 

 while the circle is being marked. 



