222 SOILS 



to a 4-inch, making the joint much more perfect 

 than if the 3-inch tile were butted against the 

 larger one. 



When buying tiles it is important to stipulate 

 that all be perfect. Some lots of tiles contain 

 many that are not fit to be used in a drainage 

 system; one poor tile may undo the work of many 

 good ones. Good drainage tiles do not crumble 

 and when struck on iron have a ringing, metallic 

 sound, not a dull, wooden sound, showing that they 

 have been well burnt. Tiles that are baaly warped 

 or chipped at the ends are worse than useless. 

 They should be smooth inside and cut square on 

 the ends. Glazed tiles are more durable than 

 unglazed, but there is little difference in efficiency. 



SIZE OF TILES 



A system of tile drainage should have sufficient 

 capacity to carry off the excess water of the heaviest 

 rains that fall, inside of twenty-four to forty-eight 

 hours. The time when under-drains are most 

 taxed is in early spring when the soil is already 

 saturated. The greater the fall of the system the 

 smaller the tiles may be, because water is carried 

 off more rapidly. Formerly 1- and 1^-inch tiles 

 were quite commonly used for lateral drains; now 

 2-inch tiles are the smallest used, for it costs but 

 little more to make them than the smaller sizes. 

 They are easier to lay to grade and safer. Two- 

 inch tiles are still used in the Eastern States, but 

 not so much as formerly, being largely replaced by 

 the 3-inch size. 



The sizes of mains and sub-mains are capable 

 of fairly accurate calculations, as their capacity 

 varies with the square of their diameters. 



