is 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
about 230 tons gross. A variation from this type has been adopted on the
Northern and Welsh sections, known as the "Precursor" class. These engines
have 5 ft. 6 in. coupled wheels, and weigh 31 tons 8 cwt. in working
order, but in other respects are very similar to the standard engines just
described; with the Scotch express, averaging in total weight 187 tons,
between Crewe and Carlisle, over heavy gradients, they burn 33 lb. of coal
per mile. These engines, although much more powerful than the standard
type, are not nearly of so handsome an appearance, the drivers seeming
much too small for the boiler under which they are placed. But by far the
boldest innovation on existing practice is the new class of compound
locomotives now being introduced by Mr. Webb. It is a six wheel engine,
with leading wheels 4 ft. diameter, and two pairs of drivers, 6 ft. 6 in.
diameter. The trailing drivers are driven by a pair of outside cylinders,
18 in. diameter and 24 in. stroke; and the leading drivers by a single
low-pressure cylinder--which takes the exhaust steam from the
high-pressure cylinders--of 26 in. diameter and 24 in. stroke, placed
under the cent