292 Ground Water, Wells and Farm Drainage. 



are broken. It will often happen that such tile may be laid 

 in place and covered before the slacking occurs. 



Besides being hard burned, strong, giving a clear ring 

 when struck and free from lime the tile should be smooth 

 and straight, with square cut ends and true circular outline 

 so "that they may be laid with close joints which will ex- 

 clude silt, 



363. How Water Enters Tile. The texture of a tile is like 

 that of common brick and will allow water to flow readily 

 through the walls, but even were the walls water tight the 

 water could still find access to the tile through the joints 

 formed by the abutting sections as rapidly as it can be 

 brought by ordinary soils requiring drainage. 



Measurements made of the rate of percolation through 

 2-inch Jefferson, Wisconsin, tile showed a flow of 8.1 cubic 

 feet per 100 feet of length in 24 hours, under a pressure of 

 23.5 inches, when surrounded by clear water only. When 

 the same tile were bedded in a fine clay loam, so that the 

 water had to percolate through the soil, the discharge was 

 reduced to 1.62 cubic feet per 24 hours and per 100 feet. 



364. The Use of Collars. It has sometimes been the 

 custom to use collars to slip over the joints formed by the 

 meeting of the sections of the tile, with the idea of better 

 excluding the silt and of holding a better alignment. The 

 collars are short sections of a size of the tile large enough 

 to slip over the joints readily. 



The use of collars is not advisable, first, on account of the 

 greater cost, and second, because when good tile are prop- 

 erly laid they are not needed. 



365. Depth at which Drains Should be Laid. It is seldom 

 necessary to lower the ground water more than four feet 

 below the surface and except in very springy places a depth 

 of 3 feet will answer most purposes. 



Since the level of the ground water changes with the 

 season and since many lands which are benefited by drain- 



