Long Boiler locomotive

Experiments at the North Midland's Derby Works showed temperatures as high as 773 °F (412 °C), determined by placing a small cup of zinc within the smokebox beneath the chimney.

Having tested the design on the North Midland line between Derby and Leeds, Stephenson took out a patent in 1842 for what he referred to as a "Long Boiler" engine.

Meanwhile, the prevailing view was that the centre of gravity should be as low as possible, which limited the size of the driving wheels, and incidentally precluded the use of inside cylinders.

The opposite point of view was taken by John Gray, who designed a number of engines for the London and Brighton Railway.

His engines were the inspiration for David Joy in his design for the Jenny Lind locomotive, which compensated for the size of its boiler by greater efficiency and a pressure of some 120 psi (830 kPa).

Picture of Kitson 'Stephenson' long boiler A No.5 taken at Middle Engine Lane station on the Stephenson Railway Museum's running line.
New South Wales railways 48 class, c. 1880
NER 1001 Class N°1275, now in the National Railway Museum , York
Circa 1852. A LNWR passenger locomotive typical of the long boiler design.