468 AGRICULTURAL ENGINEERING 



doing this is to treat the inside of the wall, as soon as the 

 forms are removed, with a wash of pure cement and water 

 reduced to the consistency of paint. This wash thoroughly 

 seals the pores of the walls and prevents the loss of mois- 

 ture and the admission of air. A coat of coal tar has been used 

 with good results, and there are many patented compounds 

 on the market which ought to be entirely satisfactory. In 

 several cases where no attempt was made to seal the walls the 

 juices of the silage apparently accomplished that result, after 

 two or three fillings, but this should not be relied upon. 



Reinforcement. Another common mistake is the lack of 

 reinforcement or the improper use of reinforcement. The 

 bursting pressure of silage is considerable, about 11 pounds 

 per square foot for each foot of depth, as an average; and this 

 pressure must be fully cared for or the walls are sure to crack. 



A mixture of one part of cement, two of sand, and four of 

 broken stone or screened gravel ought to make a good silo 

 wall. If good natural gravel and sand are at hand, a mix- 

 ture of one to five will be satisfactory. 



The Block Silo. There are two methods of using con- 

 crete: (1) in the form of blocks, which are made and cured 

 before being laid in the wall; (2) the monolithic wall, require- 

 ing the use of forms. The first method involves a large 

 amount of labor in making and handling the blocks and lay- 

 ing them in the silo wall. So much labor is involved that 

 it is likely to be the most expensive item of the entire cost. 

 The use of forms in the monolithic construction dispenses 

 with a large part of the labor, but in turn offers some serious 

 disadvantages. To obtain good, smooth walls, rather 

 expensive forms must be made; and as the silo reaches some 

 height, the forms are difficult to handle without expensive 

 scaffolding and hoisting apparatus. 



