290 ENGINEERING ON THE FARM 



above the grade line of the ditch. The tile-layer, by holding 

 a rod 5 feet in length on the bottom of the ditch, can deter- 

 mine if the ditch is at the right grade by sighting across the 

 upper end of the rod at the strings. If it is in line with the 

 strings, the ditch is at the proper grade. Hence, by testing 

 every foot of the bottom of the trench with this rod, and 

 sighting over the top of the rod at the three strings, he can 

 construct the bottom of the ditch to the exact grade. 

 When the strings are being put up, if the three are not in 

 line, it shows that there has been an error, either in the 

 surveying or in figuring the height of the strings, for the 

 three will be in line if the work is correct. Hence this method 

 of grading the bottom of the ditch is a check on the accu- 

 racy of the survey. 



Laying tile. The laying of the tile should begin at the 

 outlet and be continuous upstream. For convenience, the 

 tile should have been distributed close to the trench 

 so that they can be reached by the tile-layer without loss 

 of time. In being laid the tile should be turned until they 

 fit tightly on top, the open space being left on the under 

 side. The fit is usually best obtained in crooked tile when 

 the bowed side of the tile is turned up. When a crack of 

 over yi inch in width is left, it should be neatly covered with 

 a piece of broken tile. 



Tile up to and including 6 inches in diameter are usually 

 laid with a tile hook (Fig. 238), the workman standing on 

 the bank of the trench. The tile is picked up with the hook, 

 lowered into the trench, and turned on the hook until it will 

 fit, when it is laid in position. A sharp rap with the hook 

 on the end of the tile after it is laid often causes it to fit the 

 preceding tile more snugly. Tile hooks are not carried in 

 stock by dealers, but they can readily be made by a black- 

 smith. The hook is made of one-half inch round iron, the 

 long part being 9 inches and the short part 4 inches in length. 

 The bend is of sufficient width to admit the wall of the tile 

 without binding. The handle is a rake handle. 



