74 SILOS: CONSTRUCTION AND SERVICE 



secure a scrap of lumber to the scaffold by one nail so the 

 end, in turning about the nail, will strike the wall. 



Hoisting. Two general methods have been followed in 

 hoisting materials to the scaffold. In one method a pulley is 

 secured to the outer end of a 2x6 projecting over the wall and 

 the material is hoisted by a horse. This method is found to 

 interfere with the use of the guide of Fig. 22; therefore a der- 

 rick after the plan of Fig. 22 has been devised. 



This derrick, 48 feet high, is built of three 2x6's 16 feet 

 long, A, and six Ix6's 16 feet long, B, besides the pieces neces- 

 sary for the arm at the top. As seen in the cross-sectional 

 view in the center, the 1x6 V are nailed flatwise upon the 

 edges of the 2x6's, thus forming an I beam. All of the mem- 

 bers are so placed that no joints are closer than 5 feet 4 inches. 

 Two short 1x6 struts, E, supports each end of the 1x6 pieces, 

 C. Two No. 9 guy wires, F, are secured to the end of C 

 toward the silo and fastened to stakes driven into the ground 

 a considerable distance away from the bottom of the derrick. 

 These prevent any side motion of the arm where the pulley 

 is attached, while a third guy wire is fastened to the other 

 end of C and secures the derrick in the other direction. This 

 derrick has been thoroughly tried out with loads up to 400 

 pounds. With the usual loads of less than 100 pounds it is 

 entirely safe. The derrick itself is most easily raised by 

 being constructed on the ground and raised after the guy 

 wires, pulley and rope have been attached. 



DOOR FRAMES 



Reinforcement. The door frames are reinforced both 

 vertically and horizontally with steel having a cross-sectional 

 area equivalent to J4 square inch, or a square reinforcing 

 bar % inch by y% inch. 



