MARINE BOILERS. 



explanation by figures representing examples of particular classes 

 of them. 



29. To save space, they are constructed so as to produce the 

 necessary quantity of steam, within the smallest possible dimen- 

 sions. With this view a more extensive surface in proportion to 

 the capacity of the boiler is exposed to the action of the tire. The 

 flues, by which the flame and heated air are conducted to the 

 chimney, are generally so constructed that the heated air issuing 

 from the furnaces may be made to pass through the boiler, either 



Fig. 3. 





by a series of oblong narrow passages with flat sides, called^wes, 

 or by a multitude of tubes of small diameter, the one and the 

 other leading from the furnaces to the base of the chimney, and 

 being everywhere below the level of the water in the boiler. The 

 former are called^we boilers, and the latter tubular boilers. 



30. In the former class of boilers the flues are so formed as to 

 traverse the boiler backwards and forwards several times before 

 they terminate in the chimney. Such an arrangement renders the 

 expense/of the boilers greater than that of common land boilers, 

 but their steam-producing power is greatly augmented. Experi- 

 ments made by Mr. Watt, at Birmingham, proved that such boilers 

 with the same consumption of fuel will produce, as compared with 



K2 131 



