THE IOWA SILO 73 



then follow the end of the guide around the wall. All blocks 

 should be within less than J^ or % inch of the guide, and even 

 these variations should be gradual so as not to form shoulders 

 in the wall. 



The device is shown in Fig. 21. A piece of 1-inch, or 

 larger, straight gas pipe, indicated by A, 7 or 8 feet long may 

 be secured as a center about which to revolve a light arm, B. 

 The outer extremities of this arm, X, are hinged, in order that 

 it may not interfere with walking around the scaffold. Also, 

 when not in use, C may be placed in the position shown in the 

 figure. It is not necessary to use the guide for each block, 

 but it is convenient for determining whether or not the blocks 

 are properly placed by means of this guide, before the mortar 

 joints are pointed. 



The stand, D, is made of 2x4's or any convenient lumber 

 by means of which the gas pipe may be held in a vertical 

 position in the center of the scaffold. The collar and set 

 screw, E, are used to raise the revolving arm to a level with 

 the top of the course being laid. The upright, F, and two 

 laths, G, serve the purpose of holding B in a horizontal posi- 

 tion. 



It will be readily seen that this guide at once becomes use- 

 ful not only in securing a circular wall but in making the 

 course level, as the end of the arm, of course, revolves in a 

 horizontal plane. This device has proven itself to be very 

 convenient. In order that the pipe A may be in the center of 

 the silo after each raising of the scaffold, it is only necessary 

 to pass a plumb line from the center of the pipe through the 

 board supporting the pipe to a nail in a stake in the bottom 

 of the silo. With this as an indication of the proper location 

 of the guide stand, the latter may be moved to place and 

 nailed lightly. After raising the scaffold, the first thing to 

 do, of course, is to drop wedges between scaffold and wall or 



