DRAINAGE 



i6 7 



have been found which can be manufactured into good 

 tiles. The manufacture of drain tiles requires consider- 

 able skill as well as a due amount of business ability. 

 Some experimentation is necessary in making drain tiles 

 from any untried bed of clay. Chemical analysis is a 

 general guide as to whether the clay is of a suitable 



Figure 70. Portion of a drainage map. 



nature to " burn " and not be broken to pieces by the 

 action of the atmosphere nor by the freezing of the water 

 absorbed in the body of the burnt tile. It is always 

 wise to ship some of the clay to a factory already estab- 

 lished and have it tested, with a view of finding methods 

 of preparing and burning it, before going to the expense 

 of building a factory beside a given clay bed. Very often 

 it is necessary to mix together the surface soil and a 

 layer of clay lower down. In other cases, a layer of 

 mixed sand and clay found near at hand, when put with 

 the clay from the main layer, will give a mixture of the 



