IMPROVEMENT OF THE SOIL. 47 



of reach of the subsoil plow and frost, and at the same 

 time to render them efficient in the work they are to per- 

 form. Experience has proven that three to four feet 

 below the surface will yield the best results. The fall 

 must be sufficient to readily and rapidly carry off the 

 water entering the system. Ordinarily, three inches fall 

 to each one hundred feet distance will give a flow strong- 

 enough to meet the demands of the soil, but a greater fall 

 will yield better results. In determining the size of the 

 drain pipes the following fact must be borne in mind: 

 The smaller the pipe the more concentrated the flow and 

 the greater the chance for sweeping along solid matters, 

 and thus ridding the pipe of clogging materials. The 

 capacity of a pipe is proportionate to the square of the 

 diameter, so that a tile one inch in diameter will have 

 a capacity of one inch of water, while a pipe two inches 

 in diameter will take four inches; one three inches in 

 diameter w T ill take nine inches. As a general rule, a 

 three-inch pipe will drain two and one-half acres when 

 placed five hundred feet apart, a four-inch pipe four acres, 

 six-inch pipe nine acres, when the grades are less than 

 three feet to the hundred. 



The distance between the trenches to hold the tiles may 

 vary from fifteen to fifty feet, depending upon whether 

 the land is stiff clay or sandy. The mains must be large 

 enough to readily take the water which the laterals 

 collect and transmit to them. 



The water goes in at the joints and not through the 

 pores of the tiles, as some people assert, so that in laying 

 the system care must be taken simply to place the pipes 

 end to end without cementing or obstructing the joints, 

 and thus preventing the free and ready flow of water into 

 the system. 



The old notion of covering the land with an elaborate 

 system of piping has been abandoned, and it has been 



