DRAINAGE 91 



greater accuracy, a level-tube is sometimes placed on the 

 horizontal arm of the bracket. The height of the line above 

 the grade stake at each station is obtained by subtracting 

 the cut from the distance the line is placed above the grade 

 line. Thus, if 7 feet be selected as the length of the measur- 

 ing stick, and the cut at a certain station be 3 feet 5 inches, 

 then the line should be placed 7 feet less 3 feet 5 inches, 

 or 3 feet 7 inches above it. If this operation be performed 

 at all stations, it will be seen that the line will be parallel 

 to the bottom of the ditch and 7 feet above it. A fishline or 

 a fine wire makes an excellent line to use for this purpose, 

 as it may be stretched very tight, overcoming the sag to a 

 large extent. Some experienced tilers prefer the " target 

 method," as it is more convenient. It is, however, more pro- 

 ductive of errors. 



Selecting Tile. Great care must be used in selecting 

 drain tile. Farm drainage is too expensive for one to take 

 serious risks with tile of questionable durability. At the 

 present time there is much discussion in regard to the rela- 

 tive merits of clay and cement tile. Attention has been 

 called repeatedly to instances where both kinds have failed. 

 Clay tile has the advantage in that it has been in use a much 

 longer time than cement tile, and a good clay tile is as per- 

 manent as any material that can be secured. Careful speci- 

 fications for tile and methods for testing the same have not 

 as yet been prepared or devised. 



Clay tile should be well burned and of uniform shape and 

 color. They should be straight, with square ends, and when 

 two are held in the hands and struck together they should 

 give a good sharp ring. Large lumps of chalk or lime in the 

 clay must be guarded against. Inferior tile are those of light 

 color,, porous and laminated. These are quite sure to become 

 disintegrated when placed in the soil. 



