how the coating to be in excellent condition and the
steel underneath to be bright and clean. In some cases, where the
initial pressure and leaking between the staves of the dry pipe were
great, the escaping air and water lifted the coating into bubbles. At
some points where this lifting was great enough to rupture the asphalt,
and the soil is heavily charged with alkali, some corrosion has begun.

The integrity and impermeability of this asphalt coat are quite as vital
as constant saturation. This coating protects the entire pipe from
exterior contact with destructive agencies. With such effective exterior
protection, a constantly full pipe is not so imperative. In the exterior
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 p