Fall necessary in Tile Drainage. I consider one foot in one hundred yards the least fall to work upon with safety.
Securing Outlets. All the outlets from main-drains should be well secured against the intrusion of vermin, by a wrought-iron grating, built in mason-work. The water may flow into a stone trough provided with an overflow-pipe, by which the quantity discharged may be ascertained at any time, so as to compare the drainage before and after rain, &c.
Traps, or Silt Ponds. Where extensive drainage is carried on in low-lying districts, and the principal outlet at a considerable distance, it may be found necessary to have traps at several points where the silt from the tiles will be kept. These traps may be of cast-iron, or mason-work, cemented; and provision should be made, by which they can be cleaned out and examined regularly—the drainage at these periods also undergoing inspection at the different traps.
Plow-Draining. We have no draining-plows in use in Ireland, that I know of; the common plow is sometimes used for marking off the drains, cutting the sides, and throwing out the earth to a considerable depth, thereby lessening the manual labor considerably. Efforts have been made in England to produce an efficient implement of this description; but it would appear there is ample room for an inventive Jonathan to walk in for a profitable patent in this department, and thus add another to the many valuable ones brought out in your great country.
Case of Obstruction in Tiles. Some years since, one of the principal main-drains on this farm was observed not discharging the water freely, as it hitherto had done, after a heavy fall of rain; and the land adjoining it showed unmistakable signs of wetness. The drain was opened, and traced to the point of obstruction, which was found to be convenient to a small poplar tree, the rootlets of which made their way into the tiles, at the depth of five and a half feet, and completely filled them, in the direction of the stream, for several yards. We have some of the tiles (horse-shoe) in our museum here, as they were then lifted from the drain, showing clearly the formidable nature of the obstruction. Another serious case of obstruction has come to my knowledge, occasioned by frogs or toads getting into the tiles of the main-drain in large numbers, on account of the outlet being insufficiently protected. In this case, a large expenditure had to be incurred, to repair the damage done.
I have not observed any case of obstruction from the roots of our cultivated plants. It has been said by some that the rootlets of mangold will reach the drains under them; and, particularly, where the drains contain most water in rapid motion. I took up the tiles from a drain on this farm, in '54, which had been laid down (by a former occupier), about the year '44, at a depth not exceeding two-and-a-half feet, and not one of these was obstructed in the least degree, although parsnips, carrots, cabbages, mangolds, &c., had been grown on this field. Obstructions may occur through the agency of mineral springs; but very few cases of this nature are met with, at least in this country. I would anticipate this class of obstruction, if from the nature of the land there was reason to expect it, by increasing the fall in the drains and having traps more frequent, where the main outlets are at a distance to render them necessary. In my opinion, the roots of trees are the great intruders to be guarded against, and more particularly the soft-wooded sorts, such as poplars, willows, alders, &c. The distance of a drain from a tree ought always to be equal to the height of the latter.
Tiles flattening in the drying process. With this subject, I am not practically familiar. In most tile-works, the tiles, after passing through the moulding-machine, are placed horizontally on shelves, which rise one above another to any convenient height, on which the tiles are dried by means of heated flues which traverse the sheds where the work is carried on; or they are allowed to dry without artificial heat. I prefer the tiles prepared by the latter method, as, if sufficient time be given them to be well dried, they will burn more equally, and be more durable. The tiles will flatten more or less for the first day or two on the shelves, after which they are rolled. This is done by boys (who are provided with pieces of wood of a diameter equal to the bore of the tile when made), who very soon learn to get over a large number daily. The "roller" should have a shouldered handle attached, the whole thickness of which should not be greater than that of the tile. The shoulder is necessary to make the ends of the tiles even, that there may be no very open joints when they are placed in a drain. Once rolled, the tiles are not likely to flatten again, if the operation be performed at the proper time.
As good tiles as I ever saw were dried in a different way, and not rolled at all. As they were taken from the machine—six at a time—each carrier passed off with his tray, and placed them on end carefully, upon an even floor. When five or six rows of tiles were thus placed, the whole length of the drying-house, a board was set on edge to keep them from falling to one side; then followed five or six other rows of tiles, and so on, till the drying-ground was filled.
This was the plan adopted in a tilery near Dublin, some years ago. It is only a few days since I examined some of the tiles made at these works, which had been taken from a drain, where they had been in use for nine years; and the clear ringing sound produced by striking them against each other, showed what little effect that length of time produced upon them, and how well they had been manufactured.
Cost of Tiles. We have recently paid at the works—