44 FOREST UTILIZATION 



Boilers in common use are designated as : 

 I. Internally fired boilers, when firebox and waterbox are 

 comprised by one and the same steel shell ; so all port- 

 able boilers and all locomotive boilers. 



(a) Cornish boiler: large flues below and return flue 



above water through entire length of boiler. 



(b) Lancashire boiler: divided flue below and divided 



flue above water through entire length of boiler, 

 so as to even the draft when firing, and so 

 as to strengthen the broad heating surface. 



(c) Galloway boiler: like Cornish but V-shaped tubes 



beset the boiler proper, thus increasing the heat- 

 ing surface and strengthening the flue. 



(d) Locomotive boiler: firebox surrounded by a 



waterleg on all sides, excepting at the grate 

 below. A bank of small tubes carries gases to 

 an "extension" or "smoke box" in front of 

 smoke stack. 



II. Externally fired boilers: masonry firebox underneath 

 boiler which is traversed by a large number of tubes. 

 Gases pass first to combustion chamber at rear end and 

 then through tubes back to front. 



To II belongs the water tube boiler, with inclined tubes, 

 a horizontal top vessel and vertical tail tubes, cre- 

 ating a continuous circuit of water, 

 (a) Pointers about boilers. 



1. Twelve square feet of heating surface of 



boiler furnish one horsepower. 



2. Each nominal horsepower requires one 



cubic foot or 7^/2 gallons of water 

 per hour. 



3. Mud drum at base of boiler to receive 



impurities deposited by water. Where 

 no mud drum exists, boiler should 

 be blown off weekly through a bot- 

 tom valve (mud cock). 



4. Steam and water capacity must be suf- 



ficient to prevent any fluctuation in 

 pressure or water level. 

 5. A large water surface (horizontal ver- 

 sus upright boilers) prevents steam 

 from bearing water particles along. 

 Usefulness of dome is doubtful as a 

 means to secure the return of watery 

 particles to the boiler. 



6. Water should occupy three-quarters of 

 boiler space. 



