148 ENGINEERING FOR LAND DRAINAGE. 



When placed in the ground, however, they are durable 

 and in every way satisfactory, provided they are well 

 burned. The vitrified tile are made of clay which will 

 endure such heat that the peculiar elements which are 

 a part of their composition will form a glassy material 

 which is hard and as durable as the best quality of 

 stone. They are always desirable drain-tile. 



The manner of designating the size is by naming the 

 inside diameter, as 4-inch, 6-inch, meaning tile are 4 

 inches and 6 inches inside diameter respectively. They 

 are sold by the thousand feet or by the thousand pieces, 

 each piece supposed to be i foot long. 



The required number of junction tile for connecting 

 the several laterals with the mains should be specified, 

 as the practice of making them in the field by chip- 

 ping and breaking the tile is not to be commended. 

 The Y junction in preference to the T junction 

 should be selected. Curved tiles, such as are used in 

 making curves in sewers, are not required for drains. 

 The turns can be made sufficiently long so that the 

 ordinary tile can be used if care is taken in fitting them. 

 There is a tendency on the part of some manufacturers 

 to make the walls of tiles too thin, which causes them 

 to break too easily in handling. The following is a 

 safe minimum thickness for the walls of drain tiles: 



3 inch f inch 



4 to 5 

 6 and 7 



T/1 ** T << 



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