METHODS OF DRAINING IRRIGATED LANDS. 497 



CEMENT DRAIN TILE. 



No little discussion has arisen concerning the utility of cement tile 

 for draining seeped lands, especially those which are strongly charged 

 with alkali. The scarcity of well-burned clay tile, as well as of good 

 clay for manufacturing them, in regions where they are most needed, 

 makes it desirable to use cement if it is possible to do so. The experi- 

 ments made in 1909 by R. A. Hart, drainage engineer of this office, 

 published in the Transactions of the American Society of P^ngineers,^ 

 indicate that the presence of salts such as are found in soils hastens 

 the setting of the cement and increases its tensile strength on a 

 80-day test. Exposure for 28 days in solutions of different kinds of 

 alkali appears to point to the fact that the suli^hates attack and 

 destroy the solidity of the sample, while the chlorids and carbonates 

 do not. The evidence furnished by tiles which have been in opera- 

 tion is conflicting, some having remained intact for 10 years and 

 still manifest no sign of disintegration, while others apparently as 

 well made have failed within a year. Those who have experience 

 in the use of this material maintain that if tiles are molded from a 

 mixture of one part good cement and three parts of the aggregate 

 used in a wet state, they will resist injury by alkali. The varieties 

 of alkaline salts which are found in seeped lands is so great, and their 

 possible combinations are so numerous, that the use of cement tile 

 for draining such lands is attended with considerable risk. Ex- 

 perience so far suggests that the pipes should be made dense and 

 practically nonabsorptive if they are to be safely used in w^ater which 

 contains a considerable amount of alkaline salts from the soil. Even 

 clay tiles which are soft or poorly burned should be discarded on the 

 score of probable disintegration if they absorb w^ater freely. What 

 are known as "seconds" at sewer-pipe factories are excellent for 

 draining and are quite commonly employed where tiles of large size 

 are needed. 



WOODEN BOX DRAINS. 



The subject of material which is used for drains should not be 

 passed without reference to wooden boxes, which, of necessity, are 

 employed in many localities because more lasting material can not 

 be obtained at a reasonable cost. They serve an excellent purpose 

 while they last and have been exceedingly useful in experimental 

 drainage where the doubtful results of the experiment did not seem 

 to warrant the use of more expensive material. They are made in 

 rectangular form, with or without bottoms, according to the ground 

 in which they are to be used. If the bed upon which they are to bo 

 laid is hard clay or gravel, no bottoms are needed unless the fall of 



1 Trans. Amer. Soc. Civ. Engin., vol. 67, p. 587. 

 91SG6°— 11 32 



