272 Bulletin 254. 



clay soil to place the drains nearer than 40 feet and they may be rela- 

 tively farther apart as the soil is more coarse in texture so that in very 

 porous soil they may, in extreme cases, be as much as 300 feet apart. 



Every drainage system should begin at the outlet and this should 

 be constructed with reference to the probable area from which it will 

 be expected to carry water. Then in developing the system of laterals, 

 it is wise to select some unit or minimum interval between laterals. 

 The tile may then be put in at this interval, at twice or four times this 

 interval and if in the course of time it is found that the larger interval 

 does not give sufficiently thorough drainage, the interval may be halved 

 or quartered by the installation of additional drains without in any way 

 affecting the system. 



The following tabic shozvs the number of feet of tile required per acre 

 when placed the specified distances apart. 



20 feet apart 2205 feet 



25 " " 1760 



30 " " 1470 



40 " " 1102 



50 " " 880 



100 " " 440 



150 " " 270 



200 " " 220 



g. Kinds of tile. 



There are two general types of tile as to hardness. These are first, 

 the soft, red tile, sometimes called brick tile which have not been sub- 

 jected to great heat in burning. Second, the hard tile designated as 

 vitrified or glazed tile. Between these two types there is every gradation 

 of hardness. Next to the vitrified tile which are very expensive the 

 semi-vitrified tile is most desirable. These have only the first beginning 

 of vitrification but are far superior to the very soft types. 



The hard tile have every advantage over the soft tile for agricultural 

 purposes. The soft tile absorb large amounts of water and when they 

 are subjected to even a small amount of freezing they quickly crumble. 

 On the other hand the hard tile absorbs very little water and are no 

 more injured by freezing when wet than any ordinary resistant stone. 

 In fact hard burned tile are equally as durable as good stone. If there 

 is the least danger of the tile freezing, the hard tile should be used and 

 since they can be purchased almost as cheaply as the soft tile, there is 

 every reason for their use. The water does not enter even soft tile 

 through the walls but through the joints so the impervious character of 

 the hard tile is no objection to their use. 



Another classification may be made as to their shapes (Fig. 214). 

 The m.ost practicable forms are the round or hexagonal tile because of 

 the ease with which they may be firmly placed on the bottom of the 



