14 



nail flatwise to this frame. This will provide a jamb of 1 inch when the form 

 is removed, and if pieces of 2-inch stuff are placed flush with the front of 

 the frame, it will give a 2-inch shoulder. This form should be deep enough 

 to fit closely between the inside and outside form of the silo-moulds. The 

 doors are double, of one-inch material, with tar-paper between, and are made 

 carefully to have air-tight joints. The door openings should be no more than 

 4 feet apart. The doors are held in their places by cross-pieces of 2- by 4- 

 inch material. When fitting doors, before filling any silo, if a layer of tar 

 or building paper be placed between the jambs and the jambs and the doors, 

 it excludes the air. 



ROOF. 



The roofs of cylindrical silos may be made in several ways, but the 

 simplest of construction, and the one requiring the least amount of material, 

 is that represented in Fig. 7, which is the cone. If the silo is not larger 



(Fig. 7.) Cone-shaped roof. 



than 15 feet in diameter, no rafters need be used, and only one hoop besides 

 the circle in the centre. This circle is made of 2-inch stuff, cut in sections 

 in the form of u circle, and two layers spiked together breaking joints. 



The roof-boards are put on by nailing them to the inner circle, and to the 

 plate as shown in the drawing, the boards having been sawn diagonally, 

 making the wide and narrow ends the same relative widths as the circum- 

 ference of the outer edge of the roof and of the inner circle. If the inside 

 diameter exceeds 15 feet, use two or three hoops, according to diameter. If 

 over 18 feet, use rafters. Prepared roofings are preferred to shingles for a 

 silo-roof, as they make a tighter roof, which retains the heat in winter. Leave 



