6 BULLETIN 190_, U. S. DEPARTMENT OF AGRICULTURE. 



does not depend upon the nailing. Under ordinary conditions the 

 soil becomes compacted within a few months after installation, so that 

 the boxes hold together, although the nails may have been eaten 

 entirely away. Boxes are less liable to displacement than are tile, 

 but if the ground is very mushy it is difficult to lay the former before 

 caving takes place. Boxes are also the more likely to be buoyed 

 upward by the fluid soil, but on the other hand it is often necessary 

 to lay planks under tile to maintain grade and line, a precaution which 

 is unnecessary in the case of boxes! On the whole, however, it may 

 be said that lumber boxes should not be used where tile is available at 

 a comparable price. 



In no case should a triangular or V-shaped box, or an open-bottom 

 box be employed. 



The simplest form of lumber box drain is shown in figure 2, a. The 

 lumber runs the long way of the box and the sections may be as long 

 as 16 feet if the soil conditions warrant. If the ground tends to cave, 



Fig. 2. — Types of lumber box drains. 



shorter sections should be employed. The top is nailed tightly to the 

 sides, but the bottom is separated from the sides by short pieces of 

 lath placed at intervals of 2 or 3 feet. The sHt thus left provides for 

 the entrance of the water. In soft ground the slit should be pro- 

 tected against the entrance of silt and sand by a gravel or cinder filter. 

 One-inch lumber may be used for boxes up to 8 inches in width, and 

 2-inch lumber for boxes up to 12 inches in width. For somewhat 

 larger boxes the lumber should run crosswise, as shown in figure 2, 6. 

 It is a convenient arrangement to employ 2 by 12 inch planks for the 

 sides and to have the top and bottom pieces cut to the proper length. 

 These should be milled, as shown, to afford shoulders which wiU hold 

 the box together after the nails are destroyed. One-inch material 

 may be used for the bottoms, except in soils so fluid that an upward 

 pressure is exerted. The top pieces should fit tightly together but 

 the bottom pieces should be separated from one-fourth to one-half 

 inch to provide for the entrance of the water. Such boxes should not 

 be over 24 inches in width. 



For still lai^er sizes, 3-inch material should be used and the side 

 planks should be wider. It is not advisable to use lumber over 16 



