DRAINAGE OF IRRIGATED LAND. 7 
inches in width, however, nor to make the sides from two widths 
oleated 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 bo 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 planks. 
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 TILE. 
Clay tile, when properly made of suitable materials, are very durable 
and may be depended upon, however strongly alkaline 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 cylindrical and the ends smooth. There should be no 
serious cracks or blisters, 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 are 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. 
The carrying capacity of a tile drain depends upon the diameter 
of the tile, the slope of the drain, the accuracy with which the tiles 
are laid and the smoothness of their inner walls, and the general plan 
of the system as regards turns, changes in slope, manholes, etc. The 
carrying capacity of a box drain depends upon the above-named 
factors and upon the shape of the box, the most advantageous shape, 
so far as capacity is concerned, being that in which the width is twice 
the depth of flow. The velocity should be high enough to prevent 
