30 
The Colorado Experiment Station. 
circle was 6 inches outside of this. Then with a tiling spade we dug 
out the space between these two circles to a depth of I foot, taking 
care to keep the inner side of the trench thus formed smooth and per- 
Fig. I. Digging a pit silo. Note the concrete ring at the top of silo. 
Also the trimmer tool in place on the pipe. The test auger for sinking a 
hole for the pipe is shown at the left. (Photo by Lauck.) 
pendicular. This trench was then filled with concrete. We now 
built the adobe walls on this concrete ring, trimming the inside of 
adobe walls with the same tool we used for trimming walls of the pit. 
(See illustration of tool used for trimming walls, Cut i.) The adobe 
walls should be io inches thick. The concrete ring being only 6 inches 
thick, the adobe will lap onto the ground on the outside. In digging, 
we left an inch or two on the outside to be cut down with the trim¬ 
ming tool. This tool was made by bolting an “L” shaped knife on the 
end of a 2x4, then measuring from the knife half the diameter of the 
silo, plus one-half inch, to allow for plaster, on the 2x4 and bored a 
hole to fit on the pipe in the center of the silo. Then, by bracing in 
the manner shown in Cut 1, the 2x4 is held in a horizontal position 
and by swinging it around the pipe the walls will be trimmed per¬ 
fectly smooth and perpendicular. The edge of the knife should be 
set to draw into the wall slightly. If the ground is very dry and 
hard, some difficulty will be experienced in making the knife cut. 
but in ordinary soil the trimming is an easy job. If you should find 
the ground too hard to trim with the knife, then use it as a guide 
to trim with the pick. We were obliged to do this the last four feet 
of our last silos. 
For hoisting the dirt, we erected a crane (See Cut 2) and 
placed it so the arm would swing over either of the two silos and 
then swing outside to deposit the dirt. We used a tub made from 
