bricks.

Wood will last almost forever below the level of the drain, where it will always be saturated with water, but in the drier earth above the tile, it would be quite sure to decay.

T

The trimming and perforating of the tile is done with a "tile-pick," (Fig. 32,) the hatchet end, tolerably sharp, being used for the trimming, and the point, for making the holes. This is done by striking lightly around the circumference of the hole until the center piece falls in, or can easily be knocked in. If the hole is irregular, and does not fit the tile nicely, the open space should be covered with bits of broken tile, to keep the earth out.

Fig. 32.-PICK

FOR

DRESSING AND PER

FORATING TILE.

As fast as the laterals are laid and inspected, they should be filled in to the depth of at least a foot, to protect the tile from being broken by the falling of stones or lumps. of earth from the top, and from being displaced by water flowing in the ditch. Two or three feet of the lower end may be left uncovered until the connection with the main is finished.

In the main drains, when the tiles are of the size with which collars are used, the laying is done in the same manner. If it is necessary to use 34-inch tiles, or any larger size, much more care must be given to the closing of the joints. All tiles, in manufacture, dry more rapidly at the top, which is more exposed to the air, than at the bottom, and they are, therefore, contracted and made shorter at the top. This difference is most apparent in the larger sizes. The large round tiles, which can be laid on any side, can easily be made to form a close joint, and they should be secured in their proper position by stones or lumps of earth, wedged in between them and the sides of the ditch. The sole tiles must lie with the shortest sides

np, and usually, the space between two tiles, at the top, will be from one-quarter to one-half of an inch. To remedy this defect, and form a joint which may be protected against the entrance of earth, the bottom should be trimmed off, so as to allow the tops to come closer to gether. Any opening, of less than a quarter of an inch can be satisfactorily covered,-more than that should not be allowed. In turning corners, or in passing around curves, with large tiles, their ends must be beveled off with the pick, so as to fit nicely in this position.

The best covering for the joints of tiles which are laid without collars, is a scrap of tin, bent so as to fit their shape, scraps of leather, or bits of strong wood shavings, answer a very good purpose, though both of these latter require to be held in place by putting a little earth over their ends as soon as laid on the tile. Very small grass ropes drawn over the joints, (the ends being held down with stones or earth,) form a satisfactory covering, but care should be taken that they be not too thick. Strips of newspaper, doubled and laid over the joints, answer an excellent purpose. Care, however, should always be taken, in using any material which will decay readily, to have no more than is necessary to keep the earth out, lest, in its decay, it furnish material to be carried into the tile and obstruct the flow. This precaution becomes less necessary in the case of drains which always carry considerable streams of water, but if they are at times sluggish in their flow, too much care cannot be given to keep them free of all possible causes of obstruction. As nothing is gained by increasing the quantity of loose covering beyond what is needed to close the joints, and as such covering is only procured with some trouble, there is no reason for its extravagant use.

There seems to remain in the minds of many writers on drainage a glimmering of the old fallacy that underdrains, like open drains, receive their water from above, and it is

too commonly recommended that porous substances be placed above the tile. If, as is universally conceded, the water rises into the tile from below, this is unnecessary. The practice of covering the joints, and even covering the whole tile, (often to the depth of a foot,) with tan-bark, turf, coarse gravel, etc., is in no wise to be commended; and, while the objections to it are not necessarily very grave in all cases, it always introduces an element of insecurity, and it is a waste of money, if nothing worse.

The tile layer need not concern himself with the question of affording entrance room for the water. Let him, so far as the rude materials at hand will allow, make the joints perfectly tight, and when the water comes, it will find ample flaws in his work, and he will have been a good workman if it do not find room to flow in a current, carrying particles of dirt with it, unless muslin is used.

In ditches in which water is running at the time of laying the tiles, the process should follow closely after the grading, and the stream may even be dammed back, section after section, (a plugged tile being placed under the dam, to be afterwards replaced by a free one,) and graded, laid and covered before the water breaks in. There is one satisfaction in this kind of work, that, while it is difficult to lay the drain so thoroughly well as in a dry ditch, the amount of water is sufficient to overcome any slight ten dency to obstruction.

Connections. As has been before stated, lateral drains should always enter at the top of the main. Even in the most shallow work, the slightly decreased depth of the lateral, which this arrangement requires, is well compen sated for by the free outlet which it secures. (See Chap. 12.)

After the tile of the main, which is to receive a side drain, has been fitted to its place, and the point of junction marked, it should be taken up and perforated; then the end of the tile of the lateral should be so trimmed as

to fit the hole as accurately as may be, the large tile re place in its position, and the small one laid on it,reaching over to the floor of the lateral ditch. Then con

ect it with the lateral as previously laid, fill up solidly the space under the tile which reaches over to the top of the main, (so that it cannot become disturbed in fillmg,) and lay bits of tile, or other suitable covering, ⚫ around the connecting joint.*

When the main drain is laid with collars, it should be so arranged that, by substituting a full tile in the place of the collar, leav

ing, within it, a

space between the

smaller pipes, -a

Fig. 33.-LATERAL DRAIN ENTERING AT TOP.

connection can be made with this larger tile, as is represented in Figures 33 and 34.

Silt Basins,t-should be used at all points where a drain, after running for any considerable distance at a certain rate of fall, changes to a less rapid fall,-unless, indeed,

the diminished fall be still sufficiently great for the removal of silty matters, (say two feet or more in a hundred). They may be made in any manner which will secure a stoppage of the direct current, and afford room below the floor of the tile for the deposit of the silt which the water has carried in suspension; and they may be of any suitable material; --even a sound flour barrel will serve a pretty good

Fig. 34.-SECTIONAL VIEW OF JOINT.

*When such covering is used, it is well to cover them with a mortar of wet clay, to keep them in place until the ditches are filled.

†See a note on Silt-basins at the end of this chapter.

purpose for many years. The most complete form of basin is that represented in Figure 24. When the object is only to afford room for the collection of the silt of a considerable length of drain, and it is not thought worth while to keep open a communication with the surface, for purposes of inspection, a square box of brick work, (Fig. 35,) having a depth of one and a half or two feet below the floor of the drain,tiles for the drains being

built in the walls, and the top covered with a

broad stone, - will an- Fig. 35.-SQUARE BRICK SILT-BASIN. swer very well.

A good sort of basin, to reach to the surface of the ground, may be made of large, vitrified drain pipes, such as are used for town sewerage, having a diameter of from six to twelve inches, according to the requirements of the work. This basin is shown in Figure 36. Figure 37 represents a basin made of a 6-inch tile, similar to that described on page 130, for turning a short corner. A larger basin of the same size, cheaper than if built

Fig. 36.-SILT-BASIN OF

VITRIFIED PIPE.