4. _Outlets._ A small per-centage should be added to the items already noticed, for the cost of the general outfall, which should be secured with great care; although, from such examination as the writer has made in this country, and in England also, in the large majority of cases, drains are discharged with very little precaution to protect the outlets. Works completed under the charge of regular engineers, form an exception to this remark; and an item of 37 cents per acre, for iron outlets and masonry, is usually included in the estimated cost per acre of drainage. 5. _Collars._ It is not known to the author that collars have been at all used in America, except at the New York Central Park, in 1858; round pipes, upon which they are commonly used abroad, when used on any, not being yet much in use here. In the estimates of Mr. Denton, in his tables, collars are set down at about half the cost of the mixed tiles. The bore of them being large enough to receive the end of the tile, increases the price in proportion to the increase in size. It is believed, however, that a smaller size of tiles may prudently be used with collars than without, because the collars keep the tiles perfectly in line, and freely admit water, while they exclude roots, sand, and other obstructions. A drain laid with one and a half inch tiles with collars is, no doubt, better in any soil than two-inch tiles without collars. Some compensation for the cost of collars may thus be found in the less price of the smaller tiles. 6. _Laying._ The cost of laying tiles is so trifling as hardly to be worth estimating, except to show its insignificance. The estimate, by English engineers, is two cents per rod for "pipe laying and finishing." What is included in "finishing," does not appear. From the personal observations of the writer, it is believed that an active man may lay from 60 to 100 rods of tiles per day, in ditches well prepared. Indeed, we have seen our man James, lay twelve rods of two-inch tiles, in a four-foot ditch, in forty-five minutes, when he was not aware that he was working against time. This is at the rate of sixteen rods an hour, which would give just 160 rods, or a half-mile, in a day of ten hours. 7. _Number of Tiles to the Acre._ The number of tiles used depends, of course, upon the distances apart of the drains, and upon the length of the tiles used. The following table gives the number of tiles of various length, per acre, required at different intervals: