of steam
pressure in the cylinders is 68 lb. The weight in full working order is on
the leading wheels, 9 tons 8 cwt.; driving wheels, 11 tons 10 cwt.;
trailing wheels, 6 tons 2 cwt.; total, 27 tons. The tender weighs 171/2 tons
in working order. These engines burn about 27 lb. of coal per mile with
trains of the gross weight of 117 tons, which is not at all an economical
duty. About 1872, the weight of the heavier express trains on the
North-Western had so increased, that a new standard type for this service
was designed, and is now the standard passenger engine; it has inside
cylinders 17 in. diameter and 24 in. stroke; the driving and trailing
wheels are coupled, and are 6 ft. 6 in. diameter, and the leading wheels 3
ft. 6 in. The frames of steel are single, with inside bearings to all the
wheels, and the boiler, of steel, is 9 ft. 10 in. long and 4 ft. 2 in.
diameter. The steel used has a tensile strength of 32 to 34 tons per
square inch, all the rivets are put in by hydraulic pressure, and the
magnetic oxide on the surface of the plates where they overlap is washed
off by a little weak sal-ammoniac and water. In testing, steam is first
got up to 30 lb. on the square inch, the boiler is then allowed to cool,
it is then proved to 200 lb.
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