The cost of forms depends, again, on the cost of material and on the cost of labor. Rough lumber varies in price from twenty to forty dollars a thousand feet, board measure, delivered on the grounds, and the cost of framing and placing it varies from eight to twenty dollars per thousand, depending on the skill of the carpenters and on their daily wages. In order to estimate the cost of the lumber required for building false work, it is best to determine exactly the amount of lumber required, and get the price from a lumber yard on that quantity. Ordinarily, it is safe to say that a carpenter in building forms will be able to saw and nail in place 250 board feet per day, so that, knowing the amount of lumber to be used and the wages of the carpenter, it will be easy to determine the cost of the forms as first set up. They may be taken down and removed for the purpose of re-assembling in another place for about half the cost of placing originally, and by carefully arranging to build the forms in panels or sections, they may be removed by a carpenter at the rate of 4,000 or 5,000 board feet per day. _Valves._—In connection with a sewage-disposal plant, valves are essential at many points. At the entrance to the several parts of the settling tank, flap valves are suitable to admit or keep out sewage from the several compartments. Gate valves are used on the by-pass lines and on connecting lines between the tank and the filter beds in order to be of service when it is occasionally necessary to clean the beds. More simple valves may be used in manholes where a diversion of the flow is required and where perfect and complete water-tightness is not essential. These valves may be made of plank, sliding up and down in grooves left in the concrete walls for that purpose. Sludge valves may be made to fit in the bottom of the tank, and depend for their water-tightness on the weight of the valve itself with the aid of a rubber packing which is placed between the valve and its setting. The cost of these various kinds of valves cannot be given exactly, since their cost depends upon freight and profit of the various commission men through whom the valves are ordered, but, generally speaking, they will be found to differ but little from the costs given in the following table: TABLE Flap valve as shown in Fig. 16 $5.00 Gate valve (iron bearings) for 6–inch pipe (Fig. 13) 20.00 Gate valve (bronze bearings) for 6–inch pipe 30.00 Sludge valve as shown in Fig. 10 4.00 Iron slide valve as shown in Fig. 11 15.00