Size of Tile 451 



tile will drain 12 acres ; a 5 -inch, 20; a 6 -inch, 40 ; 

 and a 7 -inch tile 60 acres." 



In the earlier practice of underdraining with cylin- 

 drical tiles, sizes as small as 1/4 inches were used for 

 the laterals, leading the water into the mains, but the 

 general tendency has been to abandon the smaller 

 sizes and to use nothing less than 3 inches in 

 diameter, even for the laterals. The labor of making 

 the small sizes is nearly as great as that required for 

 those 3 inches in diameter, thus leaving the differ- 

 ence in cost chiefly that of the extra amount of stock 

 used in the manufacture. But the 3 -inch size is so 

 much safer to use than the smaller ones that the 

 latter should generally be abandoned. The most seri- 

 ous objection to the small sizes is the great difficulty 

 in laying them so exactly to grade as not to have 

 them silt up. 



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

 laterals, the lengths of each size used, and the dis- 

 tance between drains, can best be shown by citing a 

 specific case where the conditions to be met have 

 been considered in making the selections and adjust- 

 ments. The case selected was laid out under the 

 supervision of C. G. Elliott, C. E., and is an 80 -acre 

 farm in northern Illinois, where the soil is a deep, 

 rich, black loam, approaching muck in its lowest 

 places, and underlaid at a depth of 2.5 feet with a 

 yellow clay subsoil. The fall of the main drains in 

 this case is not less than 2 inches, per 100 feet, and 

 at of the laterals is more rather than less. 



The diagram, Fig. 141, shows that the least distance 



