DEAINAGE OF IREIGATED LAND. 7 



inches in width, however, nor to make the sides from two widths 

 cleated together. For the larger sized box drains, it is best to build 

 the box in short sections as shown in figure 2, c. This type of con- 

 duit is especially useful in bad ground, as it may be laid in much the 

 same manner as tile. The lumber should be milled to provide 

 shoulders. The sections should interlock, as shown in figure 2, c. 

 These shoulders may be easily and cheaply cut by passing each end 

 of the top and bottom pieces over a circular saw, the latter being so 

 set as to cut out a rabbet as deep as the thickness of the saw and as 

 wide as the thickness of the side planlis. 



CEMENT TILE. 



The use of cement tile has occasioned much discussion, owing to the 

 failure of lean, improperly-made tile. However, even the best of 

 cement tile is open to suspicion where sodium or magnesium sulphates 

 are present in the soil. Cement tile should be made very rich, usually 

 not leaner than 1:2:4; the materials should be well gauged, mixed 

 very wet, and carefully tamped into form, after which the tile must be 

 properly cured, preferably by steam. These requirements absolutely 

 ehminate hand-tamped tile made so dry that they may be taken from 

 the forms at once. 



CLAY TELE. 



Clay tile, when properly made of suitable materials, are very durable 

 and may be depended upon, however strongly alkahne the drain 

 water may be. They should be vitrified and as impervious as possible; 

 the walls should be smooth and of fairly uniform thickness; the bore 

 should be cyhndrical and the ends smooth. There should be no 

 serious cracks or bhstere, and the content of foreign material should 

 be small. Lime, especially, should be avoided. The tiles usually 

 come in lengths of either 1 or 2 feet in the smaller sizes, and 3 feet in 

 the larger sizes. Under ordinary circumstances the 2-foot length 

 is preferable for the smaller sizes, as tiles of this length ^re more 

 easily handled and keep their positions better, while sufficient inlet 

 area is afforded by the 2-foot spacing of joints. The walls should be 

 sufficiently thick to give the tile the strength necessary to withstand 

 the pressure of the saturated earth. 



SIZE OF CONDUIT. 



Th(! currying (capacity of a tile draiji depends upon the diameter 

 of the tile, 1 \u\ slope of the drain, the accuracy with which the tiles 

 are laid and \\u' smoothness of tlx'ir inner walls, and the general plan 

 of the system as regards tums, changes in slop(!, manJiolos, etc. The 

 carrying capacity of a box draiji depends upon the above-named 

 factors and upon th(! shu])c of the 1k)X, the most ndvantagiunis shnpe, 

 so far as capH(;ity is conctrnu^d, bcijig that in which i\w width is twice 

 the depth of flow. Tlu; velocity should be high (^n(n^gh to prevent 



