profit and contingencies, the latter amount when the work is to be done under great risks and subject to possible losses. Out of a dozen bids made on one sewer contract there are generally one or two quite low, two or three others quite high, and the remainder more or less close together midway between these, and usually representing a fair price for the work, which also the engineer's estimate should do. The estimate should not be too low, as this often gives rise to suspicion of intentional deception, and if made the basis of an appropriation of funds for construction may lead to a forced curtailment of the amount of work done. On the other hand, an unduly high estimate may discourage any appropriation whatever. Probably no act of the sewerage engineer is more readily appreciated by the public at large than the making of an estimate closely approximating the actual cost. The cost of brick, lumber, and sand varies with each locality and should be obtained from local dealers. That of cement and pipe varies little except with the freight, and this variation is slight between different places in the same section and on main freight-lines. A schedule price has been adopted by all sewer-pipe makers, from which large discounts are allowed. Such a list is given below. The discount allowed contractors for car-load lots at present (1902) near New York City is about 70 to 72 per cent for sizes under 24 inches. TABLE NO. 17. LIST PRICES OF VITRIFIED CLAY SEWER-PIPE, AND WEIGHTS OF Slants are charged three times as much as plain pipe, and measured on the long side of the slant, but none less than 12 inches long. Each additional branch or trap is charged branch price. Double-strength pipe is allowed 10 per cent less discount than standard pipe. Increasers are pipe with the hub on the small end and reducers with the hub on the large end, and are charged double the price of 2 feet of pipe of the size of the large end. Channel or split pipe, which is pipe cut in two or more pieces lengthwise, costs the price of whole pipe. Stoppers or plugs for closing pipe cost as much as I foot of pipe of the size in which they are used. 36- and 38-inch WOODEN-STAVE PIPE in Los Angeles, Cal., cost $2.25 to $2.50 per foot, complete.* Light-weight CAST-IRON PIPE, first quality, cost in 1902 about as follows: Size, inches... TABLE NO. 19. COST OF LIGHT IRON PIPE. 4 6 8 10 12 14 16 18 20 22 24 27 30 33 .40.52 .77 .961.101.30 L.50 2.00 2.25 2.75 3.10 3.75 4.15 Cost per foot.. 30 One barrel of cement, used neat, should lay the following lengths of sewer, pipes 3 feet long: TABLE NO. 20. LENGTHS OF PIPE SEWER ONE BARREL OF CEMENT WILL LAY. The following gives approximately the lowest practicable cost of excavating trenches in compact loam or material * See also "Water-supply Engineering," page 448. excavated with equal ease. The prices for shoring and sheathing are to be added where necessary. These are based on continuous work with gangs of the most economical size. House-connections or other short lines would cost more. Profit is not included. Trench machines excavate at a cost of 12 to 18 cents per cu. yd., plus $175 to $400 per month rental. TABLE NO. 21. COST OF EXCAVATING AND BACK-FILLING AND OF SHEATHING; DOLLARS PER LINEAL FOOT. (Compact Loam; No Ground-water; No Machinery.) used the second time, the third time, the fourth time. With care good sheathing may be used an average of five times. two to ten times the above. ROCK EXCAVATION in sewercents to $2 per cubic yard. QUICKSAND may cost from No estimate can be given for it. trenches usually costs from 75 The greater the amount of rock per running foot to be excavated the more cheaply it can be done. The approximate cost of laying sewer-pipe, including all but the excavation, is given in the following table: TABLE NO. 22. COST OF LAYING SEWER-PIPE, CENTS PER LINEAL FOOT. and distributing. 0.15 0.18 0.21 0.35 0.38 0.41 0.63 0.90 1.20 1.50 2.10 Laying, cost of jute, calking. Cement, mixed. Total 3.00 4.00 4.46 5.25 1.23 1.38 1.55 1.62 1.78 1.97 2.31 2.58 3.00 3.704 50 5.06 5.48 6.00 6.80 0.44 0.50 0.55 0.58 0.65 0.75 0.93 1.11 1.32 1.55 2.00 2.35 2 90 3.86 4.57 1.82 2.06 2.31 2.55 2.81 3.13 3.87 4.59 5.52 6.75 8.60 10.41 12 38 14.32 16.62 * Teams hauling 4500 pounds per load; average haul one mile; $3.50 per day. The approximate cost of building circular brick sewers is given in the following table. This does not include excavation or back-filling. The approximate cost of manholes, 3 feet by 4 feet 6 inches on the bottom, is given in the following table. A 4-foot circular manhole will cost about 4 per cent more. This table does not include the cost of the iron-work. The brickwork is taken as 8 inches thick down to a depth of 12 feet, and below this as 12 inches thick. Foundations of concrete 6 inches thick, with benches for 8-inch pipe $3.25 $3.60-$16.00 20 cts. In the above tables labor is taken at $1.50 per day, teams at $3.50. The cost given does not include superintendence, use of tools, profit, or any of the general expenses of manage ment, but is thought to be liberal, and sufficient to include. these under good management. Natural CEMENT can be had in the Eastern States at from 65 cents up, Portland from $1.80 up, per barrel in car-load lots. The cost of SAND will vary with the locality from 25 cents to $2 per cubic yard. ART. 58. METHODS OF ASSESSMENT. While not an engineering feature of sewer construction, the methods employed in paying for a system may be briefly considered to advantage. In many cases the city pays for the construction and later reimburses itself by special assessments on benefited property or by annual rental; in some the entire cost is borne by the city at large; in others part is borne by the city, part by the property-owners. The city's payment may be made from the ordinary funds or by issuing sewerage bonds. In Philadelphia, Pa., the assessment bills. are assigned to the contractor, with right of lien for collection. Probably no better general statement of sewer-assessment methods in this country could be given than by quoting from an article on the "Theory and Practice of Special Assessments," by J. L. Van Ornum in volume XXXVIII of the Transactions of the American Society of Civil Engineers (September, 1897): "In a majority of cases the city pays for main sewers, either wholly or all above the usual assessment for a branch sewer. A large number also assess this expense by the area method upon the property affected, either entirely or all exceeding the usual charge for a lateral, as before. Less commonly a percentage is assessed and the city pays the balance, or the cost is divided between an area and a frontage charge, or other plans are followed in its distribution. Of the |