BOILERS, FUELS AND FLUES 



205 



Cast and Wrought-Iron Boilers. The 



cast-iron boiler has a size limit above which 

 it is impracticable to go, though two or more 

 may be joined in a series. It is also claimed 

 that on account of the thickness of the walls 



Fig. 104. End view of "square" sectional 



boiler showing fire travel. A and B, push 



nipples for joining sections 



it is less economical of fuel than are wrought- 

 iron boilers, which have thinner walls. On 

 the other hand, cast-iron boilers do not rust 

 as badly as wrought-iron ones when not in 

 use, and they have no flues to be burned out 

 by the sulphurous gases resulting from the 



