No. 4.] HINTS OX LAND DRAINAGE. 379 



rarely exceed the full capacity of a two-inch tile with round 

 bore, laid at such a grade or foil that the water flowing 

 through the same will carry along such line silt as may un- 

 avoidably enter at the joints, say not flatter than three to 

 four inches in a hundred feet. With a fall of six inches in 

 a hundred feet the same size of tile will carry the water 

 collected by about fifteen hundred feet of drains, and will 

 therefore be sufficient for an acre and one half of land; 

 while with a foil of twelve inches in a hundred feet two-inch 

 tile will serve about tw T o thousand feet of drains, or two 

 acres of porous land. 



In clayey lands less of the rainfall percolates into the 

 soil, consequently drains therein will receive a smaller 

 quantity of water per acre, wdiich in ordinary practice may 

 be assumed to be about one-half as great as that in lands 

 underlaid by free water-bearing sand. Therefore the same 

 size of tile or capacity of main drain will suffice for about 

 double the area of clayey subsoils that would be needful for 

 sandy subsoils ; and, inasmuch as the drains should be placed 

 at about one-half the distance in clayey soil, it follows that 

 the amount or length of drain that may be discharged through 

 a two-inch tile for such lands is about four times as great as 

 in those having a free subsoil. Thus, while a thousand feet 

 of two-inch tile, laid forty-five feet apart in a free subsoil, 

 will serve one acre, four thousand feet of the same size, laid 

 twenty-two and one-half feet apart, will serve two acres of 

 clay land. 



The relative capacities of different sizes of tiles are ap- 

 proximately as follows, that of a two-inch tile being in- 

 dicated by 1, to wit : — 



Capacity of two-inch tile equals, 1.00 



Capacity of two-and-one-half-inch tile equals, .... 1.50 



Capacity of three-inch tile equals, 2.50 



Capacity of four-inch tile equals, 5.00 



Capacity of five-inch tile equals, 7.50 



Capacity of six-inch tile equals, .12.50 



Capacity of eight-inch tile equals, 25.00 



Thus for land requiring two-inch tile to carry the maxi- 

 mum drainage from one acre, a main drain of four-inch tile 



