74 LAND DRAINAGE 



On the precautions to be exercised in the choice of 

 drain tile, Fippin writes as follows : l 



" The preeminent material for modern land drainage is 

 tile. It comes in different shapes and quality. By a 

 process of evolution we have come to prefer round or 

 hexagonal tiles because they are easiest to lay and least 

 likely to clog. They may be made of burned clay or of 

 concrete. Clay tile may be either vitrified or unverified. 

 The former is the more durable because its walls are less 

 porous. The difference lies in the quality of clay used 

 and the degree of heat applied in burning. Vitrification 

 means partial melting of the clay particles, which run 

 together in a very dense mass. A low degree of porosity 

 coincident with a moderate degree of vitrification is 

 especially desired where the tile is likely to freeze. In 

 the soil the pores in the tile become filled with water, 

 and if it freezes in this condition the walls of the tile 

 may be fractured and broken up into scales. If even 

 one or two tiles in a long line are thus destroyed, the 

 service of the drain is jeopardized. Since vitrified tile 

 costs no more on the average than soft tile, there is no 

 excuse for taking the risk in using the soft tile. The 

 drainage efficiency of the tile is not affected by the dif- 

 ference in the porosity of the walls, since the water enters 

 at the joints. 



" Cement tile that are of fairly good quality may be 

 made by hand or in machines. It is doubtful whether 

 they can be made as durable as the best clay tile. They 

 should be carefully made of a rich mixture. Sand that is a 

 little loamy improves the quality, if the mixing is thorough, 

 as it reduces the amount of pore space. Whether cement 

 tile can be made at prices to compete with clay tile depends 

 1 Cornell Reading-Courses, iv. No. 78 (1914). 



