protection of the wood, this coated pipe has quite an advantage over continuous stave pipe.

Each piece of pipe goes directly from the winder to the asphalt rolls, then to an adjacent saw-dust table, then back to the rolls, then to the table again, and then to the dry finishing rolls at the opposite end of the table. The coating thus consists of two layers of asphalt and two of saw-dust. When the pipe leaves the finishing rolls, the coat is hard and smooth and about 1 3/16 in. thick. This describes the coating as done at Bay City, Mich.

At Elmira, N.Y., one application of asphalt and saw-dust only, without a finishing dry roll, completed the work; but the band was run through a bath of hot asphalt as it was wound, thus coating its underside also. This initial treatment of the band on the Wykoff pipe is necessary because the exterior of the stave is neither planed nor turned to a circle. The exterior of the pipe forms a polygon, and the band is in perfect contact only at the angles. The theory in regard to the Michigan pipe is that the perfect contact of the band and the wood on the true exterior circle excludes air from the under surface of the metal, and prevents corrosion. Experience appears to justify this theory.

Cast-iron Pipe.—Beginning at the first pumping plant at Coyote, at Mile 156, and running up to Mile 166, and again commencing at the Luna pumps, at Mile 171, and extending up to Mile 179, the minimum pressure on those portions of the pump main is more than the 130 lb. per sq. in. allowed for wood pipe, and the final estimated maximum pressures run up to 310 lb.

The selection of iron pipe for these pressures was, first, as between steel and cast-iron; and, second, as between the lead joint of the standard bell and spigot pipe and the machined iron joint of the universal joint pipe. Again, the choice was as between lead and leadite for the bell and spigot pipe.

Cast iron was selected because of the certainty of its long life, and the bell and spigot pipe was selected on the basis of comparative costs for pipe laid. The standard lead joint was chosen on the result of tests. This cast-iron pumping main has a diameter of 12 in. throughout.

Pipe Weights.—Makers of standard bell and spigot pipe urged the usual heavy weights selected for municipal service and heavy water-hammer. Three pressures, viz., 217, 260, and 304 lb., were used for the division of pipe weights, on which the standard pipe-makers specified shell thicknesses of 0.82, 0.89, and 0.97 in. Eliminating water-hammer and adopting a working stress of 2400 lb., the thicknesses are reduced to 0.54, 0.65, and 0.76 in. To make the latter conform to the specifications of the New England Water-Works Association, the pipe was cast to 0.57, 0.65, and 0.77 in. The reduction in cost amounts to $52,811.

By the provision of air-cushions, hereafter described, the writer's anticipation of no water-hammer on the pumping main has been fully realized.

The pipe was manufactured and inspected under the above-mentioned specifications.

Pipe Joints.—There was a question about the reliability of the lead joint at 300 lb. The writer had a section of 12-in. pipe, with standard joints containing 22 lb. of lead, laid and tested to 500 lb. without sign of failure or leakage. The joints were caulked down 3/16 in. below the face of the bell. Of 8,700 joints thus made in the field, not one has blown out or failed. A few weeped slightly on top, and they were made permanently tight by additional caulking. The present maximum pressure is 278 lb. These joints are the standard joints specified by the New England Water-Works Association. It should be borne in mind that there is no water-hammer on this line. In 8,700 joints, 198,000 lb. of lead and 3,200 lb. of oakum were used, or 22.76 and 0.37 lb. per joint.

Leadite was tested in competition with lead, but it leaked at 100 lb. and failed under a sustained pressure of 300 lb. It is a friable material, and cannot be caulked successfully. Its principal ingredient appears to be sulphur. The failure was by slow creeping out of the joints. It is melted and poured, but not caulked. It has attractive features for low pressures and for lines not subject to movement or heavy jarring.

Air-Cushions.—To prevent water-hammer on the pumping main, all pumps are provided with large air-chambers. In addition, and as the special feature for absorbing the shock of pumping under high pressure through a pipe 21 miles long, a large air-chamber in the form of a closed steel cylinder, 5 ft. in diameter and 15 ft. long, is mounted on the pumping main outside of the pump-house. This cylinder is set on its side, in concrete collars, directly over the pipe beneath, to which it is connected by a 12-in. tee, in which a 12-in. gate-valve is set. The cylinder is provided with a glass gauge, cocks, etc. It was designed for a working pressure of 300 lb., and, at each pumping plant, it has proved to be entirely air-and water-tight. As indicated by sensitive gauges on the pump main, just beyond these large air-chambers, the latter absorb all the water-hammer which gets beyond the air-chamber on the pumps.

Air-Pumps.—Each pumping plant is provided with four automatic air-charging devices, connecting to all air-chambers of the pumps and to the air-chamber on the pumping main. They are of the Nordberg type, and have proved very efficient. They are operated only a part of the time; otherwise, they accumulate too much air in the chambers.

Air-Valves.—On the entire line there are 144 automatic air-valves made by the United States Metal Manufacturing Company, of Berwick, Pa. They are working satisfactorily.

Gate-Valves.—In addition to the customary gate-and check-valves at the reservoirs and pumping stations, gate-valves are located at necessary points and elevations in the line to control the flow of water and keep the pipe full, even to the extent of closing all such valves tight and holding the line full without flow. This is for the purpose of delivering through a full pipe any desired quantity of water less than that required to keep the open pipe full. This, of course, is on account of the wood pipe. As the differences of elevations are very great on the gravity sections of the line, and as any one valve might inadvertently become closed tight when other valves above would be open, the bursting of the pipe under such conditions is prevented either by a pressure relief valve attached to and immediately above the gate-valve, or by an open stand-pipe erected on some suitable elevation between the valves. This is more clearly shown on the profile, Plate V, of the ground line and the hydraulic grades of the pipe line. An inspection of this profile will show that these controlling valves are located so that, when closed, the pressure against them does not rise above the maximum pressure on the section above, due to the hydraulic grade of the line when carrying its full capacity.

Safety Valves.—To prevent rupture of the pipe or injury to the pumps, in case the pumping mains should become obstructed, a 6-in. pop safety valve is mounted on the main just beyond the large air-chamber already described. These valves are set to release at the maximum working pressure of the pumps when the regular quantity of water is being pumped, and they are piped to the adjacent reservoir, so that there is no loss from them.

Check-Valves.—Check-valves are placed in the pumping main to prevent the backward flow of water. There is one near the pumps, and one at the upper end and outside of the reservoir into which the main discharges.

Blow-Off Valves.—These valves are located in all material valleys or depressions.

Stand-Pipes.—Between the gate-valves, at certain points where the maximum hydraulic grade is not more than 60 ft. above the surface of the ground, open stand-pipes are erected. If the grade line is too high, relief-valves