TENTH ANNUAL YEAR BOOK— PART X 423 



the swelling action of the staves. The form of reinforcement which has 

 been found the most convenient for the Iowa silo is hard black, No. 3 

 steel wire which is laid in the mortar joints as described later. 



Some silo walls have ben known to crumple at the bottom, due to the 

 weight of the walls themselves and to the friction of the silage. The 

 4-inch block wall of a 16-foot Iowa silo, 35 feet high, will carry not only- 

 its own weight at the bottom, but that of all the silage which could be 

 placed in the silo several times over. 



When constructed of curved blocks, the Iowa silo has been made reas- 

 onably smooth on the inside, there has been no loss of silage from the 

 roughness of the wall. Silo No. 1, which was constructed of 16-inch 

 blocks with little curvature, permitted a few air pockets to form, result- 

 ing in a small amount of spoiled silage after being stored in the silo for 

 two years. 



DURABILITY. 



The walls of the Iowa silo are constructed of hollow, vitrified clay 

 building blocks which, as far as weather resistance i-s concerned, are as 

 durable as any building material which can be obtained. Their durability 

 corresponds with the durability of brick which is to be found in all parts 

 of the state. This does not mean that all hollow building blocks are 

 durable, for there are good and bad blocks on the market. Good blocks 

 are so plentiful that no one need make the mistake of selecting blocks 

 of questionable merit. A discussion of the quality of blocks is given 

 later. 



The roof of the Iowa silo, like the walls, is made of durable material. 

 A cheaper roof may be used if desired, but it is strongly advised that the 

 concrete roof be used Avhere possible. 



One common mistake met with in silo construction is that the door 

 frame is made of material which will soon decay or rust and have to be 

 replaced. The door frame of the Iowa silo is made of reinforced con- 

 crete which, when properly constructed, should be as durable as the 

 walls themselves. 



The materials used in the Iowa silo will resist decay, disintegration, 

 the action of frost, and any implied or real action of the acidity of the 

 silage. Even the steel which is placed in the mortar joints and concrete 

 door frame as reinforcement, is thoroughly protected from rust. So care- 

 fully has the matter of durability been considered in the design of the 

 Iowa silo that it would be difficult to estimate its life. When carefully 

 built it ought to last for several generations. 



The doors of the Iowa silo are designed to be made of wood. They will 

 decay and must be replaced after several years. The convenience and low 

 cost of the wooden doors, which may be easily replaced, justifies their use. 



CARE AND REPAIR. 



The Iowa silo when properly constructed is practically free from any 

 expense for repair and maintenance. The only possible expense may be the 

 occasional washing of the inside of the walls at intervals of not less than 

 fivp years, with a cement wash and the replacement of the doors after they 

 have become rotten from use. 



