STEAM BOILER

A ve el in which water is converted into steam for the purpose of supplying steam engines, or for any other purposes for which steam is used in the arts, or in domestic economy. The most common form of boiler used for steam engines is that called the wagon boiler, an isometric view of which is given in the cut. The form of boiler adopted by Watt consisted of a semi-cylindrical top, flat perpendicular sides, flat ends, and a slightly concave bottom. That which is represented in the cut has sides a little concave. The steam v. >ed in these boilers does not exceed the pre ure of the atmosphere by more than 5 lbs. per square inch; and the sides and ends, though not so favourable to strength as the cylindrical form, are sufficiently strong for this pre ure. In a boiler of this form the air and smoke, pa ing through flues that are carried round it, are in contact at one side only with the boiler. The brickwork or other materials forming the1160flue must therefore be non-conductors of heat, [s. 1180]