ferent
sizes to be purchased, reference should be had to the following figures;
the first 2,000 feet of drains require a collecting drain of 2-1/4-inch
tile, which will take the water from 7,000 feet; and for the outlet of
from 7,000 to 20,000 feet 3-1/2-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 increased, but
in such ground, there is usually rock enough or such accumulations of
boulders in some parts, to reduce 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 thousand,--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 t