446 Irrigation and Drainage 



The facts are, however, that there is so ready a 

 movement through the walls of ordinary tiles them- 

 selves, and through the joints when they are made as 

 perfect as possible, that every precaution should be 

 taken in laying tiles to make perfect joints, in order 

 that the silt and soil may be excluded, to prevent 

 clogging the drain. 



A series of observations on 2 -inch Jefferson, Wis., 

 tiles, relating to the rate of percolation through the 

 pores in the walls, showed that under a pressure of 

 23.5 inches the discharge per 100 feet into the tile was 

 at the rate of 8.1 cubic feet during 24 hours. This 

 occurred when the walls were surrounded by water 

 only. When the tiles were covered with a fine clay 

 loam, so that water had to flow through 3 inches of 

 this soil to reach the tiles, the discharge was reduced 

 to the rate of 1.62 cubic feet per 100 feet of tile in 

 24 hours. It is plain, therefore, that with this poros- 

 ity and with the openings at the joints, there is 

 ample opportunity for the water to find its way into 

 the drains after reaching them, and great pains 

 should always be taken to make as close joints as 

 possible. 



The use of collars to keep sediment from entering 

 the joints is not a good practice. They will not, as 

 a rule, fit closely ; they tend to encourage careless 

 laying ; they increase the first cost, and the soil, if 

 it works under the collars so as to fill the space, will 

 retard the entrance of water into the drain. Tile well 

 made, with ends square and Avhole, if properly laid, 

 make a sufficiently close joint, 



