THE IRRIGATION AGE. 



1103 



a circle, which are covered with sheet metal or wooden 

 lagging. Each piece must be long enough to provide for 

 a 6-foot 3-inch length of the circumference of the circle as 

 well as several inches for the lap or strap joints. The 

 forms are raised by loosening them at the joints and set- 

 ting them up again on the finished section of the silo. 



Mixing and Placing the Concrete. 



Concrete for silos should be rich in Portland cement 

 and should be put into the forms mushy wet. Mix it 1 

 part cement to 2 parts sarjd to 4 parts crushed rock. Four 

 parts of clean pit or bank-run gravel may be used instead of 

 the sand and rock. Measure all materials on the basis that 1 

 bag of cement equals 1 cubic foot. Many persons raise the 

 concrete in buckets, but the work can be done more 

 quickly and easily by using a horse, together with a der- 

 rick or a well braced jib-boom fixed to an adjoining 

 building. 



Building the Silo. 



The finished silo 

 shown above is 15 

 feet in diameter (in- 

 side) and 36 feet 

 high, of which 4 feet 

 is below ground. At 

 odd times all of the 

 materials were hauled, 

 so that there would be 

 no delay when the 

 work was started. 

 After the pit was dug 

 to solid clay, the con- 

 crete footings (2 feet 

 wide and 1 foot thick) 

 were placed, and a 4- 

 inch concrete floor 

 was laid upon the nat- 

 ural clay bottom. The 

 next day the forms 

 were set up, the re- 

 inforcement placed, 

 and the walls begun. 

 These forms were 4 

 feet high and were 

 made in eight sec- 

 tions 6 feet 3 inches 

 long. 



Since silage con- 

 tains so much water, 

 steel rods are neces- 

 sary as reinforcement to withstand the pressure. To get 

 the best results, this reinforcing should be placed exactly 

 1J-2 inches from the outside of the silo wall. Rods 

 54-inch in diameter and 10 feet long were used. The ver- 

 tical rods were spaced 18 inches apart. Measuring down 

 from the top of the silo, the horizontal rods were spared 

 as shown in the tables below. 



Spacing of Horizontal Reinforcement. 



Feet distant from top 40-35 35-30 30-35 25-30 20-15 15-10 10-0 



Spacing in inches 6 7 8 10 12 15 18 



The horizontal rods were carefully made into solid hoops 

 by bending the ends so as to hook together. They were 

 also wired to the inside of the vertical rods. (Complete 

 plans for silos may be obtained free from any Portland 

 cement company.) Two extra lengths were placed in the 

 concrete l l / 2 inches above the door openings for removing 

 the silage. These openings were made by a removable 

 form (also cut to the circle), which fitted snugly be- 

 tween the molds for the silo wall. 



The silo forms were filled with concrete and allowed 

 to stand over night. The next morning they were loos- 

 ened, raised and again filled. These operations were re- 

 peated daily until the side walls were finished. 



With a 4-inch concrete roof, the silo is entirely fire- 

 and repair-proof. The roof was built on a temporary 

 wooden roof, which was entirely removed after three 

 weeks. The concrete roof is cone-shaped with a rise in 

 the center of 2 feet and a drip or overhang of 1 foot. One 

 inch from the under side, this roof is reinforced with 

 J't-inch rods laid like the spokes of a wheel and spaced 18 

 inches at the rim. Every other rod reached only half- 

 way to the peak of the roof. To hold the spokes in posi- 

 tion so that the concrete could be forced between them 



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TV: 



and the temporary wooden roof, one ring of f^-inch rods 

 was wired to this reinforcing just over the side walls and 

 another half-way to the peak. These rods strengthen the 

 roof greatly and must not be left out. Water-soaked 

 weather boards were used to form the circular edge of the 

 roof. An opening for the blower tube from the cutter 

 was formed in the silo roof in the same manner as the 

 doors in the side walls. 



The Cost of Concrete Silos. 



The list of materials required for this silo is given 

 below together .with a very liberal estimate of the cost of 

 the same. The silo was built by five farm laborers in 

 thirteen days. As a raise was made each day, the four 

 extra days were spent in framing the forms, digging the 

 pit and building the roof. The owner used gravel from 

 his own farm pit instead of stone and sand. 



BILL OF MATERIALS. 

 Crushed rock, or screened gravel ...... 40 cu. yds. at $1.10....$ 44.00 



Sand ................................ 20 cu. yds. at $1.00 ---- 20.00 



Portland cement ....................... 54 barrels at $2.50 ---- 135.00 



Reinforcing, 425 pieces of ^6-inch x 



10-foot rods ....................... 1504 pounds at $0.03 'A... 39.10 



$238.10 



The first cost of 

 concrete silos may 

 or may not be great- 

 er than that of the 

 best of any other 

 kind. The time is 

 now at hand when 

 farmers, like rail- 

 roads and corpora- 

 tions, are consider- 

 ing the lasting qual- 

 ities of buildings. 

 Concrete silos need 

 no insurance; they 

 do not blow down 

 or burn up. They 

 never have to be 

 painted or repaired. 

 With other kinds of 

 silos during their 

 short lives, these ex- 

 penses alone equal 

 the first cost. Con- 

 crete lasts forever. 



The two cuts shown 

 herewith give a good 

 idea of the work. 



OUR UNDERGROUND WATERS. 



Water is found in some amount in all formations be- 

 low the earth's surface, from the loosest and most porous 

 sands and gravels to the hardest slate and granite. The 

 amount varies from the merest trace chemically combined 

 in the molecules of the rocks to immense reservoirs which 

 supply wells flowing hundreds of thousands of gallons a 

 ^day. Some waters are so pure that a refined chemical 

 snalysis shows only minute traces of organic and mineral 

 matter; others are so heavily charged with minerals or 

 ether impurities as to be unsuitable for use. 



The slope of the surface at any point is one factor 

 determining the amount of water absorbed by the ground. 

 The direction and amount of slope also determine the 

 form of the water table that is, of the upper limit of 

 saturation. Except where the surface is flat the water 

 table is generally not parallel with the surface; it is almost 

 invariably farthest from the surface on the summits of 

 hills and mountains and nearest to it in valleys and along 

 the coast, reaching the surface in swamps and along 

 rivers, lakes, and beaches. The surface of the water table 

 K always in motion, its higher portions flowing toward 

 the lowest outlets along rivers or the sea. This direction 

 of flow explains why fresh water is usually found when 

 a well is dug in a sandy beach. From Water-Supply 

 Paper 223, United States Geological Survey. 



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