7 ft. 6 in. diameter, and leading and trailing wheels 3 ft. 6 in.
diameter, with a total wheel base of 15 ft. 5 in. The frames are single,
with inside bearings to all the wheels. The boiler is 11 ft. long and 4
ft. diameter, and the heating surface is in the tubes, 1,013 feet;
fire-box, 85 ft.; total, 1,098 feet. The tractive power per lb. 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 17½ 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. with hydraulic pressure, and afterward to 160
lb. with steam. The fire-box is of copper, fitted with a fire brick arch
for coal burning, and the grate area is 15 square feet. The heating
surface is, in the tubes, 1,013 square feet; fire-box, 89 square feet;
total, 1,102 square feet. The wheel base is 15 ft. 8 in., and the tractive
power 88 lb. for each lb. of steam pressure in the cylinders. These
engines, working the fast passenger trains at a speed of about 45 miles
per hour, burn about 35 lb. of coal per mile, when taking trains weighing