DRAINAGE 
takes the place of that removed by per- 
colation. Water moves downward and 
laterally toward the drain, and the lateral 
distance through which the drain will 
relieve the soil of water is governed by 
the resistance which the soil particles 
offer to the flow of water among them. 
This process does not leave the soil with- 
out moisture, but simply removes the 
excess or free water and makes more 
room for the storage of capillary or 
usable water. It does not remove the 
free water from points below the level of 
the drain. The free water removed by 
tile drains may come from rain, or it may 
come from seepage. 
Kinds of Tile 
1. Red tile. 
2. Vitrified. 
3. Cement—except the very large 
ones——is more expensive than the red clay 
tile. Jt becomes harder as it ages, and 
is more durable. 
The tile should be round in form, 
straight, and every particle of clay used 
in making them should be completely 
burned. Such a tile will last indefinitely 
in earth and water. Where exposed to 
long-continued freezing and thawing, as 
at the outlet, the best vitrified tile should 
be used. After one has become familiar 
with the product of a given factory, pro- 
perly burned tiles may be readily dis- 
tinguished by their color and by their 
ring when struck with a piece of steel. 
Good clay may be semi-vitrified by skil- 
ful burning. Porosity of the finished 
tile is not important, since the per cent 
of water that passes through the walls 
of the tile is very small. Vitrification is 
desirable. 
Systems of Drainage 
Mains, sub-mains, laterals. 
Single, double, natural, grouping, grid- 
iron, parallel. 
The natural and grouping systems are 
used where the aim is not to secure per- 
fect drainage, but rather so nearly suffi- 
cient for ordinary crops as to make the 
increase in yield pay a fair return for 
the money invested. They can be used 
to remove water that has collected in 
low places. 
901 
Compare the amount of double drain- 
ing with the gridiron system and parallel 
system. The latter has the advantage 
here, but long parallel lines will require 
large tile, or else many junctions. The 
parallel system is generally the best. 
Depth, Frequency and Size of Tile 
Principles of Drainage—In general 
we should drain the land where the water 
collects. 
1. Lay the mains in the line of natu- 
ral drainage, except where a “cut-off” 
will be in line of economy. 
2. Lay the laterals in the line of 
greatest slope, otherwise the water may 
ooze out of the tile in the upper part of 
its course. 
8. Use long parallel laterals in place 
of short ones where possible. 
4, Make the lines straight and with 
easy curves-—easy to lay. 
5. Bring all the land needing drainage 
under the influence of the drains. 
6. Use the level wherever in doubt. 
In addition to this, keep the water 
spread out. Small tile are cheaper. 
Depth, Frequency and Size of Tile— 
These three factors are closely related 
and constitute the most important part 
of drainage. These factors will depend 
on—- 
1. The character of the soil and sub- 
soil. 
2. The amount and distribution of 
rainfall. 
3. The topography of the surface. 
4. The crop to be grown. 
5. Prevalence of underground water. 
6. Level of the ground water. 
The system should always be arranged 
with reference to these conditions. 
Depth 
The depth must be such that water can 
get to the tile before it shall have caused 
serious injury to the crop. The drain 
should be near the water to be removed, 
and below the bulk of the roots. This 
necessitates that it be shallower in 
clay to work properly. In coarse texture 
soils the drains attain their full efficiency 
almost at once, but in dense clay there is 
an increasing efficiency as the soil be- 
comes granulated and the system is estab- 
