[CHAPTER II.]
BOILERS.
The first boilers were made as a single cylinder of wrought iron set in brick work, with provision for a fire under one end. This was used for many years, but it produced steam very slowly and with great waste of fuel.
The first improvement to be made in this was a fire flue running the whole length of the interior of the boiler, with the fire in one end of the flue. This fire flue was entirely surrounded by water.
Then a boiler was made with two flues that came together at the smoke-box end. First one flue was fired and then the other, alternately, the clear heat of one burning the smoke of the other when it came into the common passage.
The next step was to introduce conical tubes by which the water could circulate through the main fire flue (Galloway boiler).
FIG. 1. ORR & SEMBOWER’S STANDARD HORIZONTAL BOILER, WITH FULL-ARCH FRONT SETTING.
The object of all these improvements was to get larger heating surface. To make steam rapidly and economically, the heating surface must be as large as possible.
FIG. 2. GAAR, SCOTT & CO.’S LOCOMOTIVE BOILER.