424 IRRIGATION FARMING. 



machine used in laying this system is illustrated in 

 Fig. 25, Chapter VIII. 



Another form of tile consists of short lengths of 

 cement pipe made in sheet-iron molds, which have 

 their joints closed with cement when they are laid. 

 These distributing pipes are often connec5led into sys- 

 tems of considerable size by being joined at one end to 

 a main supply pipe, which is generally of sheet iron 

 coated with asbestos. Sometimes what is known as 

 laminated pipe, which consists of two thicknesses, is 

 used. This may be made of two pipes of such a size 

 that when placed one within the other there will be a 

 space of one-sixteenth of an inch between them, which 

 space is filled with asbestos, while the inner and outer 

 surfaces are coated with the same material; or it may 

 be made from one piece of sheet iron rolled so that it 

 will form a double thickness of iron. The elbows and 

 T's are of iron laid in cement. When used for irri- 

 gating small fruits and vegetables, the laterals are 

 placed twelve to twenty feet apart and the holes are 

 at intervals of from six to eight feet. 



Tiling. — Scientists who have given thought to the 

 subje<5l are agreed that, theoretically, subirrigation by 

 porous tiles is the ideal plan. The tiles may be made 

 porous by mixing sawdust with the mortar, which being 

 burned out in the baking process leaves the tiles 

 porous to the exa(5l degree desired and prepared for in 

 the mixing. The first cost of laying a system of pipes 

 has been estimated at $400 an acre. The tiling has the 

 advantage of furnishing drainage when there is too 

 much water in the soil. The ground is first graded 

 and leveled, and a ditch is dug with plows and spades 



