in of loose dirt in laying, and giving twice the space for the entrance of water at the joints. A chief advantage of the larger sizes is, that they may be laid on any side. and thus made to fit closely. The usual sizes of these tiles are 1 inches, 24 inches, and 3 inches in interior diameter. Sections of the 2 inch make collars for the 1

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Fig. 16.-ROUND TILE AND COLLAR, AND THE SAME AS LAID. inch, and sections of the 3 inch make collars for the 21 inch. The 3 inch size does not need collars, as it is easily secured in place, and is only used where the flow of water would be sufficient to wash out the slight quantity of foreign matters that might enter at the joints.

The size of tile to be used is a question of consequence. In England, 1-inch pipes are frequently used, but 1 inch* are recommended for the smallest drains. Beyond this limit, the proper size to select is, the smallest that can convey the water which will ordinarily reach it after a heavy rain. The smaller the pipe, the more concentrated the flow, and, consequently, the more thoroughly obstructions will be removed, and the occasional flushing of the pipe, when it is taxed, for a few hours, to its utmost capacity, will insure a thorough cleansing. No inconvenience can result from the fact that, on rare occasions, the drain is unable, for a short time, to discharge all the water that reaches it, and if collars are used, or if the clay be well packed about the pipes, there need be no fear of the tile being displaced by the pressure. An idea of the drying capacity of a 1-inch tile may be gained from observing its wetting capacity, by connecting a pipe of this size with

*Taking the difference of friction into consideration, 14 inch pipes have fully twice the discharging capacity of 1-inch pipes.

a sufficient body of water, at its surface, and discharging over a level dry field, all the water which it will carry. A 12-inch pipe will remove all the water which would fall on an acre of land in a very heavy rain, in 24 hours,much less time than the water would occupy in getting t the tile, in any soil which required draining; and tiles of this size are ample for the draining of two acres. In like manner, 24-inch tile will suffice for eight, and 31-inch tile for twenty acres. The foregoing estimates are, of course, made on the supposition that only the water which falls on the land, (storm water,) is to be removed. For main drains, when greater capacity is required, two tiles may be laid, (side by side,) or in such cases the larger sizes of sole tiles may be used, being somewhat cheaper. Where the drains are laid 40 feet apart, about 1,000 tiles per acre will be required, and, in estimating the quantity of tiles of the different sizes to be purchased, reference should be had to the following figures; the first 2,000 feet of drains require a collecting drain of 24-inch tile, which will take the water from 7,000 feet; and for the outlet of from 7,000 to 20,000 feet 3-inch tile may be used. Collars, being more subject to breakage, should be ordered in somewhat larger quantities.

Of course, such guessing at what is required, which is especially uncertain if the surface of the ground is so irregular as to require much deviation from regular parallel lines, is obviated by the careful preparation of a plan of the work, which enables us to measure, beforehand, the length of drain requiring the different sizes of conduit and, as tiles are usually made one or two inches more than a foot long, a thousand of them will lay a thousand feet,leaving a sufficient allowance for breakage, and for such slight deviations of the lines as may be necessary to pass around those stones which are too large to remove. In very stony ground, the length of lines is often materially in creased, but in such ground, there is usually rock enough

or such accumulations of boulders in some parts, to re duce the length of drain which it is possible to lay, at least as much as the deviations will increase it.

It is always best to make a contract for tile considerably in advance. The prices which are given in the advertisements of the makers, are those at which a single thou sand, or even a few hundred,-can be purchased, and very considerable reductions of price may be secured on large orders. Especially is this the case if the land is so situated that the tile may be purchased at either one of two tile works,-for the prices of all are extravagantly high, and manufacturers will submit to large discounts rather than lose an important order.

It is especially recommended, in making the contract, to stipulate that every tile shall be hard-burned, and that those which will not give a clear ring when struck with a metallic instrument, shall be rejected, and the cost of their transportation borne by the maker. The tiles used in the Central Park drainage were all tested with the aid of a bit of steel which had, at one end, a cutting edge. With this instrument each tile was "sounded," and its hardness was tested by scraping the square edge of the bore. If it did not "ring" when struck, or if the edge was easily cut, it was rejected. From the first cargo there were many thrown out, but as soon as the maker saw that they were really inspected, he sent tile of good quality only. Care should also be taken that no over-burned tile,—such as have been melted and warped, or very much contracted in size by too great heat,-be smuggled into the count.

A little practice will enable an ordinary workman to throw out those which are imperfect, and, as a single tile which is so underdone that it will not last, or which, from over-burning, has too small an orifice, may destroy a long drain, or a whole system of drains, the inspection should be thorough.

The collars should be examined with equal care. Con cerning the use of these, Gisborne says:

"To one advantage which is derived from the use of "collars we have not yet adverted--the increased facility "with which free water existing in the soil can find entrance into the conduit. The collar for a 1-inch pipe 'has a circumference of three inches. The whole space "between the collar and the pipe on each side of the "collar is open, and affords no resistance to the en"trance of water; while at the same time the superin"cumbent arch of the collar protects the junction of two "pipes from the intrusion of particles of soil. We con❝fess to some original misgivings that a pipe resting only "on an inch at each end, and lying hollow, might prove "weak and liable to fracture by weight pressing on it "from above; but the fear was illusory. Small particles "of soil trickle down the sides of every drain, and the "first flow of water will deposit them in the vacant space "between the two collars. The bottom, if at all soft, will also swell up into any vacancy. Practically, if you reopen a drain well laid with pipes and collars, you will "find them reposing in a beautiful nidus, which, when they are carefully removed, looks exactly as if it had been "moulded for them."

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The cost of collars should not be considered an objec tion to their use; because, without collars it would not be safe, (as it is difficult to make the orifices of two pieces come exactly opposite to each other,) to use less than 2inch tiles, while, with collars, 1-inch are sufficient for the same use, and, including the cost of collars, are hardly more expensive.

It is usual, in all works on agricultural drainage, to insert tables and formulæ for the guidance of those who are to determine the size of tile required to discharge the water of a certain area. The practice is not adopted here,

for the reason that all such tables are without practical va.ue. The smoothness and uniformity of the bore; the rate of fall; the depth of the drain, and consequent "head," or pressure, of the water; the different effects of different soils in retarding the flow of the water to the drain; the different degrees to which angles in the line of tile affect the flow; the degree of acceleration of the flow which is caused by greater or less additions to the stream at the junction of branch drains; and other considerations, arising at every step of the calculation, render it impossible to apply delicate mathematical rules to work which is, at best, rude and unmathematical in the extreme. In sewerage, and the water supply of towns, such tables are useful, though, even in the most perfect of these operations, engineers always make large allowances for circumstances whose influence cannot be exactly meas ured, but in land drainage, the ordinary rules of hydrau lics have to be considered in so many different bearings. that the computations of the books are not at all reliable. For instance, Messrs. Shedd & Edson, of Boston, have prepared a series of tables, based on Smeaton's experi ments, for the different sizes of tile, laid at different inclinations, in which they state that 1-inch tile, laid with a fall of one foot in a length of one hundred feet, will discharge 12,054.81 gallons of water in 24 hours. This is equal to a rain-fall of over 350 inches per year on an acre of land. As the average annual rain-fall in the United States is about 40 inches, at least one-half of which is removed by evaporation, it would follow, from this table, that a 1-inch pipe, with the above named fall, would serve for the drainage of about 17 acres. But the calcu lation is again disturbed by the fact that the rain-fall is not evenly distributed over all the days of the year,-as much as six inches having been known to fall in a single 24 hours, (amounting to about 150,000 gallons per acre,) and the removal of this water in a single day would re