Size of Tile. 301 



friction on the walls of small tile and the disturbance due 

 to eddies set up at the joints are greater in proportion to the 

 amount of water carried the capacities of tile, running full, 

 increase faster than the squares of their inside diameters. 



4. It is seldom advisable to use tile smaller than 3 inches 

 in diameter because so little variation above or below a true 

 grade will fill them with sediment. 



5. The size of mains must vary with the area they are to 

 drain, with their fall and their length. C. G. Elliott states 

 that where drains are laid 3 feet or more deep, and on a 

 grade not less than 3 inches in 100 feet, a 2-inch main not 

 more than 500 feet long will drain 2 acres. 



A three inch tile will drain 5 acres. 



A four " " " " 12 " 



A five " ' 20 " 



A six ' " .. 40 " 



He specifies further that a 2 inch main should not be 

 laid longer than 500 feet and a 3 inch not longer than 1,000 

 feet. 



375. A Practical Illustration of Sizes and Distances Apart 

 of Drains. The sizes of mains and sub-mains, the sizes of 

 laterals, the lengths of each size used and the distance be- 

 tween drains may be most clearly and briefly stated by 

 citing a practical example. The case selected is an SO acre 

 field laid out under the direction of C. G. Elliott where the 

 soil is a rich black loam approaching muck in its lowest 

 places and at 2.5 feet underlaid with a yellow clay subsoil. 

 The fall of the main is not less than 2 inches in 100 feet, 

 the laterals being more rather than less. This area is repre- 

 sented in Fig. 120. 



The main begins with 1,000 feet of T inch tile carrying 

 the water from 80 acres of flat land surrounded by level 

 fields. Next follow 1,200 feet of 6 inch, then 600 feet of 5 

 inch and closing with 157 feet of 4 inch tile into which no 

 laterals lead. Nothing smaller than 3 inch tile are used for 



