278 SOILING CROPS AND THE SILO. 



stone, concrete or grout, bricks and metal. More 

 than one class of the materials named is sometimes 

 used in building the same silo. They are desig- 

 nated chiefly by the material used in their construc- 

 tion. For instance a stone silo though lined with 

 bricks is usually spoken of as a stone silo. 



Metal silos, according to Prof. Woll, are built of 

 homogenous steel plate, lapped and double riveted 

 so as to make them tight. They are objectionable, 

 at present, because of their cost ; because of the ease 

 with which frost penetrates them and because of 

 the quickness with which they corrode. It has been 

 computed that they cost about twice as much as 

 stone silos of similar capacity, while the latter are 

 much more enduring. Being easily penetrated by 

 frost, this one objection would render them unsuit- 

 able for use in a northern climate. Nor has any 

 preservative been found up to the present time that 

 can be applied to them inside which will effectively 

 resist for any lengthened period the corroding in- 

 fluences of the silage juices. Because of these 

 objections, metal silos will not be further considered. 



Concrete or grout silos have the walls made of 

 small stones held together by well tempered mortar. 

 In localities where the materials of construction 

 abound, it may be proper to use them, but since in 

 cold climates the walls must be protected by an outer 

 lining of wood with an air space between, their 

 construction, at the best, is costly. When used they 

 should be built circular in form, if practicable in the 

 location chosen, to facilitate the even settling of the 

 silage, and they should also be lined inside with 

 cement, or, if unprotected outside, with bricks and 



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